| 1. |
- Abenoza, Roberto, et al.
(författare)
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Individual, Travel, and Bus Stop Characteristics Influencing Travelers’ Safety Perceptions
- 2018
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Ingår i: TRR Journal of transportation research board. - : Sage Publications. - 0361-1981.
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Tidskriftsartikel (refereegranskat)abstract
- Ensuring safety during door-to-door public transport trips is a fundamental challenge to service providers as safety influences individuals’ mobility. Using reported safety perceptions of travelers waiting at six bus stops with different characteristics in Stockholm, this study investigates factors that have an impact on determining travelers’ perceived safety and crime perceptions. This is done by assessing the importance of real-time information provision and the environmental characteristics of bus stops during the day and at night for different types of crime, after controlling for travelers’ individual and trip characteristics, and their previous experiences of victimization. Interaction effects of age, gender, and travel frequency are also tested. The results suggest that bus shelter characteristics, natural surveillance, and trustworthy real-time information are the most important factors influencing safety and crime perceptions. Additionally, safety perceptions are strongly influenced by previous experiences of victimization. The effect of perceived feelings about crime and safety are found to be nuanced by age and gender. Unlike some common beliefs, travelers: (1) feel less worried about becoming a victim of crime at bus stops associated with high crime rates; (2) prefer opaque shelters at night; and (3) have higher safety perceptions when the stop is located in an area of mixed land use. The impact of a bus stop’s number of passers-by is found to be insignificant. No direct or indirect effects can be attributed to frequency of travel by bus, indicating that familiar places and routine behavior have noeffect on declared crime and safety perceptions.
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| 2. |
- Allström, Andreas, 1978-, et al.
(författare)
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Hybrid Approach for Short-Term Traffic State and Travel Time Prediction on Highways
- 2016
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Ingår i: Transportation Research Record. - Washington, DC, USA : The National Academies of Sciences, Engineering, and Medicine. - 0361-1981 .- 2169-4052. ; 2554, s. 60-68
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Tidskriftsartikel (refereegranskat)abstract
- Traffic management and traffic information are essential in urban areas and require reliable knowledge about the current and future traffic state. Parametric and nonparametric traffic state prediction techniques have previously been developed with different advantages and shortcomings. While nonparametric prediction has shown good results for predicting the traffic state during recurrent traffic conditions, parametric traffic state prediction can be used during nonrecurring traffic conditions, such as incidents and events. Hybrid approaches have previously been proposed; these approaches combine the two prediction paradigms by using nonparametric methods for predicting boundary conditions used in a parametric method. In this paper, parametric and nonparametric traffic state prediction techniques are instead combined through assimilation in an ensemble Kalman filter. For nonparametric prediction, a neural network method is adopted; the parametric prediction is carried out with a cell transmission model with velocity as state. The results show that the hybrid approach can improve travel time prediction of journeys planned to commence 15 to 30 min into the future, with a prediction horizon of up to 50 min ahead in time to allow the journey to be completed
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| 3. |
- Ames, Alicia, et al.
(författare)
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Transport Workers' Perspective on Indigenous Transport and Climate Change Adaptation
- 2014
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2451, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the potential role of indigenous transport for increasing the adaptive capacity of selected cities in developing Asia. Indigenous transport drivers were surveyed face-to-face in Bandung, Indonesia, and in Ho Chi Minh City, Vietnam, to gain an understanding of how transport workers, specifically drivers-operators, characterize transport modes considered as indigenous and perceive their potential role in increasing the adaptive capacity of these cities. The main finding was that indigenous transport modes in the two cities in the case study had evolved to fit a niche market influenced by differing urban scales and divergent demographic and geographic characteristics. Thus, the experiences and the perceptions of transport workers on indigenous transport were highly contextualized in relation to service and route characteristics. Operating conditions for drivers were indicative of the regulatory status of indigenous transport modes in the informal landscape. This analysis contributes to an increased understanding of the role and the operation of indigenous transport modes within the transport system. The analysis also contributes policy-relevant insights to improve an understanding of the potential role of indigenous transport in climate change adaptation, as well as to increase awareness and to anticipate a shift to a more environmentally sustainable transport mode.
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| 4. |
- Andreasson, Ingmar J.
(författare)
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Personal Rapid Transit as Feeder-Distributor to Rail
- 2012
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2275, s. 88-93
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Tidskriftsartikel (refereegranskat)abstract
- Efficient feeder distributor systems around train stations are important in attracting train passengers. Such systems would be a suitable application for personal rapid transit (PRT). This paper suggests layouts and operations strategies for transfer stations between PRT and heavy rail. Ticket handling can be avoided by having the train fare include PRT trips. Ridesharing can be encouraged by destination signs. The catchment area that can be efficiently served is related to the interval between trains. The capacity of the station and guideway can be improved by coupling PRT vehicles in the station and decoupling them as necessary en route. Applications in Sweden are illustrated with the PRTsim software. In one case, outgoing PRT vehicles were loaded to 78%.
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| 5. |
- Antoniou, Constantinos, et al.
(författare)
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Estimation of Traffic Dynamics Models with Machine Learning Methods
- 2006
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Ingår i: Transportation Research Record. - 0361-1981 .- 2169-4052. ; 1965, s. 103-111
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Tidskriftsartikel (refereegranskat)abstract
- Speed-density relationships are a classic way of modeling stationary traffic relationships. Besides offering valuable insight into traffic stream flows, such relationships are widely used in dynamic traffic assignment (DTA) systems. In this research, an alternative paradigm for traffic dynamics models, appropriate for traffic simulation models and based on machine-learning approaches such as k-means clustering, k-nearest-neighborhood classification, and locally weighted regression is proposed. Although these models may not provide as much insight into traffic flow theory as speed-density relationships do, they allow for easy incorporation of additional information to speed estimation and hence may be more appropriate for use in DTA models, especially simulation-based models. This paper (with data from a network in Irvine, California) demonstrates that such machine-learning methods can considerably improve the accuracy of speed estimation.
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| 6. |
- Antoniou, C, et al.
(författare)
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Incorporating Automated Vehicle Identification Data into Origin-Destination Estimation
- 2004
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Ingår i: TRANSPORTATION NETWORK MODELING 2004. - Istanbul, Turkey : SAGE Publications. ; , s. 37-44
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Konferensbidrag (refereegranskat)abstract
- A methodology for the incorporation of automated vehicle identification (AVI) data into origin-destination (O-D) estimation and prediction is presented. AVI technologies facilitate the collection of useful data, such as point-to-point travel times and subpath flows. A framework for the incorporation of AVI data into the well-established O-D estimation and prediction process is presented. Improvements are proposed for both the formulation and the inputs to the O-D estimation and prediction model. Furthermore, as the O-D estimation and prediction process is often used in the traffic estimation and prediction context, approaches to the incorporation of AVI data into other areas of the dynamic traffic assignment framework are outlined. Performance and computational issues are also considered, and the results of a case study are presented to demonstrate the approach.
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| 7. |
- Antoniou, Constantinos, et al.
(författare)
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On-line Calibration of Traffic Prediction Models
- 2005
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Ingår i: Transportation Research Record. - 0361-1981 .- 2169-4052. ; 1934, s. 235-245
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Tidskriftsartikel (refereegranskat)abstract
- A methodology for the on-line calibration of the speed-density relationship is formulated as a flexible state-space model. Applicable solution approaches are discussed and three of them (extended Kalman filter (EKF), iterated EKF, and unscented Kalman filter (UKF) are selected and presented in detail. An application of the methodology with freeway sensor data from two networks in Europe and the U.S. is presented. The improvement in the estimation and prediction of speeds due to on-line calibration (compared with the speeds obtained from the off-line calibrated relationship) is demonstrated. The EKF provides the most straightforward solution to this problem, and indeed achieves considerable improvements in estimation and prediction accuracy. The benefits obtained from the -more computationally expensive-iterated EKF algorithm are shown. An innovative solution technique (the UKF) is also presented. The UKF has a number of unique qualities and advantages over the EKF, including no assumption of analytical representation of the model and no need for explicit computation of derivatives. Empirical results suggest that the UKF outperforms the other two solution techniques in prediction accuracy.
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| 8. |
- Balakrishna, Ramachandran, et al.
(författare)
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A Simulation-based Evaluation of Advanced Traveler Information Systems
- 2005
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Ingår i: Transportation Research Record. - : Transportation Research Board of the National Academies. - 0361-1981 .- 2169-4052. ; 1910, s. 90-98
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Tidskriftsartikel (refereegranskat)abstract
- Traveler information has the potential to reduce travel times and improve their reliability. Studies have verified that driver overreaction from the dissemination of information can be eliminated through prediction-based route guidance that uses short-term forecasts of network state. Critical off-line tests of advanced dynamic traffic assignment-based prediction systems have been limited, since the system being evaluated has also been used as the test bed. This paper outlines a detailed simulation-based laboratory for the objective and independent evaluation of advanced traveler information systems, a laboratory with the flexibility to analyze the impacts of various design parameters and modeling errors on the quality of the generated guidance. MITSIMLab, a system for the evaluation of advanced traffic management systems, is integrated with Dynamic Network Assignment for the Management of Information to Travelers (DynaMIT), a simulation-based decision support system designed to generate prediction-based route guidance. Evaluation criteria and requirements for the closed-loop integration of MITSIMLab and DynaMIT are discussed. Detailed case studies demonstrating the evaluation methodology and sensitivity of DynaMIT's guidance are presented.
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| 9. |
- Balakrishna, R., et al.
(författare)
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Calibration of Microscopic Traffic Simulation Models : Methods and Application
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :1999, s. 198-207
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical framework and a solution approach are presented for the simultaneous calibration of the demand and supply parameters and inputs to microscopic traffic simulation models as well as a large-scale application emphasizing practical issues. Microscopic traffic simulation models provide detailed estimates of evolving network conditions by modeling time-varying demand patterns and individual drivers' detailed behavioral decisions. Such models are composed of elements that simulate different demand and supply processes and their complex interactions. Several model inputs (such as origin-destination flows) and parameters (car-following and lane-changing coefficients) must be specified before these simulation tools can be applied, and their values must be determined so that the simulation output accurately replicates the reality reflected in traffic measurements. A methodology is presented here for simultaneously estimating all microscopic simulation model parameters by using general traffic measurements. A large-scale case study for the calibration of the MITSimLab microscopic traffic simulation model by using the network of Lower Westchester County, New York, is employed to demonstrate the feasibility, application, and benefits of the proposed methodology.
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| 10. |
- Balakrishna, Ramachandran, et al.
(författare)
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Incorporating Within-Day Transitions in Simultaneous Offline Estimation of Dynamic Origin-Destination Flows Without Assignment Matrices
- 2008
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2085, s. 31-38
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Tidskriftsartikel (refereegranskat)abstract
- An offline methodology is presented: it simultaneously estimates dynamic origin-destination (O-D) matrices, without using assignment matrices that incorporate within-day transition equations. The proposed formulation and solution approach extends a calibration method recently developed that directly uses the output of any network loading model (such as a dynamic traffic assignment or simulation model) so that the complex relationships between O-D flows and model outputs are accurately captured (as opposed to the more common method of approximate linear relationships based oil file assignment matrix). The study extends the original formulation by incorporating spatial and temporal relationships among various O-D flows (transition equations). These transition equations link O-D flow variables across time intervals in such it way that known structural demand patterns can be preserved in the new estimates. Such transition equations, although common in the context of real-time O-D flows, complicate the offline simultaneous estimation of O-D flows and have not been used to their full potential in the past. The approach is demonstrated through a case study.
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| 11. |
- Balakrishna, Ramachandran, et al.
(författare)
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Offline calibration of dynamic traffic assignment : Simultaneous Demand-and-Supply Estimation
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2003, s. 50-58
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Tidskriftsartikel (refereegranskat)abstract
- Advances in intelligent transportation systems have resulted in deployment of surveillance systems that automatically collect and store extensive networkwide traffic data. Dynamic traffic assignment (DTA) models have been developed for a variety of dynamic traffic management applications. They are designed to estimate and predict the evolution of congestion with detailed models and algorithms that capture travel demand and network supply and their complex interactions. The availability of rich time-varying traffic data spanning multiple days provides the opportunity to calibrate a DTA model’s inputs and parameters offline so that its outputs reflect field conditions in future offline and online real-time applications. The state of the art of DTA model calibration is a sequential approach, with supply model calibration (assuming known demand inputs) followed by demand calibration with fixed supply parameters. An offline DTA model calibration methodology is presented for simultaneous estimation of all demand-and-supply inputs and parameters, with sensor data. A minimization formulation that can use any general traffic data and present scalable solution approaches for the complex, nonlinear, stochastic optimization problem is adopted. A case study with DynaMIT, a DTA model with traffic estimation and prediction capabilities, is used to demonstrate and validate the methodology. Archived sensor data and a network from Los Angeles, California, are used to demonstrate scalability. Results indicate that the simultaneous approach significantly outperforms the sequential state of the art in terms of modeling accuracy and computational efficiency.
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| 12. |
- Bayarma, Alexander, et al.
(författare)
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On the recurrence of daily travel patterns : A stochastic-process approach to multi-day travel behavior
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; 2021, s. 55-63
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Tidskriftsartikel (refereegranskat)abstract
- Multiday travel behavior was examined as a stochastic process, and new empirical findings are offered on the variation of travel patterns from day to day. The analysis was based on data from a 6-week travel diary survey conducted in Germany. A small number of travel pattern classes were identified, and transitions in the patterns over a course of weeks were analyzed with Markov chain models. Transitions from a pattern to itself are frequent, particularly for nonworkers, and indicate that some patterns tend to be pursued for a large number of consecutive days. The study also reveals that individuals are heterogeneous in terms of multiday travel behavior; pattern-to-pattern transition probabilities vary substantially across individuals. Some of the observable heterogeneity is demonstrated in terms of the association between attributes of the individual and the recurrence of daily travel patterns.
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| 13. |
- Bierlaire, Michel, et al.
(författare)
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An analysis of the implicit choice set generation using the constrained multinomial logit model
- 2010
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; 2175, s. 92-97
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Tidskriftsartikel (refereegranskat)abstract
- Discrete choice models are defined conditional to the analyst's knowledge of the actual choice set. The common practice for many years has been to assume that individual-based choice sets can be deterministically generated on the basis of the choice context and characteristics of the decision maker. This assumption is not valid or not applicable in many situations, and probabilistic choice set formation procedures must be considered. The constrained multinomial logit model (CMNL) has recently been proposed as a convenient way to deal with this issue, as it is also appropriate for models with a large choice set. In this paper, how well the implicit choice set generation of the CMNL approximates the explicit choice set generation is analyzed as described in earlier research. The results based on synthetic data show that the implicit choice set generation model may be a poor approximation of the explicit model
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| 14. |
- Bindra, Sumit, et al.
(författare)
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Predicting Segment-Intersection Crashes with Land Development Data
- 2009
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981. ; :2102, s. 9-17
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Tidskriftsartikel (refereegranskat)abstract
- Experience with crash prediction modeling has confirmed the importance of traffic volume, not only as exposure but also as a predictive variable. For intersection-related collisions, for example, angle collisions or any collisions involving turning vehicles, traffic volumes on both intersecting roads are necessary for sufficient prediction of crash count These collisions occur not only at intersections but any place where vehicles turn on or off the roadway, such as driveways. Intersecting traffic volumes at such locations are either not available or labor intensive to acquire. The objective of this study was to investigate the use of geographic information system (GIS) land use inventories to supplement observed traffic volumes as exposure measures for estimating models for predicting segment-intersection crashes, defined as collisions occurring on road segments involving one or more turning or crossing vehicles. Model results for rural two-lane and urban two- and four-lane undivided roads indicate that the number of trips generated and the extent of surrounding land development itself act as excellent predictors for segment-intersection crashes and in fact work better than models using the number of access points. The reason is that those variables better describe the intensity of the traffic accessing the major artery. This is a valuable finding, since access points along a road segment cannot be counted automatically, but many jurisdictions have GIS land use inventories available for all sorts of planning purposes. Such a development will permit better accounting of exposure to segment-intersection crashes in crash prediction modeling.
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| 15. |
- Birgisson, Björn, et al.
(författare)
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American Road Map for Research for Nanotechnology-Based Concrete Materials
- 2010
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2142, s. 130-137
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical behavior of concrete materials depends to a large extent on structural elements and phenomena that are effective on micro- and nanoscales. The nanomodification of concrete materials has the potential to open up new uses and classes of concrete materials, with wide-ranging implications for the concrete transportation infrastructure. The development of nanotechnology-based concrete materials will require a multidisciplinary approach, consisting of teams of civil engineers, chemists, physicists, and materials scientists. To help develop nanotechnology-based concrete materials, a concentrated effort was undertaken in the United States to develop a national road map for research in this area. This effort included two National Science Foundation (NSF) workshops held in August 2006 and September 2007. In addition to NSF, the Portland Cement Association, the Defense Threat Reduction Agency, the Florida Concrete and Products Association, the Army Corps of Engineers, TRB, and the International Union of Testing and Research Laboratories for Materials and Structures sponsored this effort. The road map for nanotechnology-based concrete materials charts a path beginning with current nanotechnology capabilities to advanced materials and systems. The road map details key milestones and step-by-step short-term, intermediate, and long-term courses of development that must take place to reach these key milestones. The road map also serves as a tool to identify the gap between the basic concrete materials of today and the potential of nanosystems and nanomaterials interacting in concrete nano-houses, nano-bridges, and nano-pavements. The national road map for nanotechnology-based concrete is described and discussed.
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| 16. |
- Birgisson, Björn, et al.
(författare)
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Development of new moisture-conditioning procedure for hot-mix asphalt
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2001, s. 46-55
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Tidskriftsartikel (refereegranskat)abstract
- The presence of pore water in mixtures can cause premature failure of hot-mix asphalt pavements. The processes typically associated with moisture damage are complex and occur over a long period of time in the field. Short of being able to simulate each of the possible mechanisms of moisture damage directly, the ideal laboratory-based conditioning system should accelerate the penetration of moisture through the asphalt film and at the same time minimize complicating effects. This paper presents the results of an experiment conducted to determine whether it was possible to use cyclic pore pressures to induce enough damage to distinguish between mixtures known to be highly resistant from mixtures known to be susceptible to moisture damage. Experimental constraints included requirements that conditioning be accomplished within a reasonable length of time and that typical laboratory equipment be used. Evaluation of the resulting effects of moisture damage included the use of the Superpave (R) indirect tension test and the energy ratio parameter. Findings show that cyclic pore pressures can be used to accelerate moisture damage enough to distinguish between mixtures known to be strippers and those known to be highly resistant to moisture damage. The use of cyclic pore pressures to accelerate moisture damage in mixtures may minimize the introduction of other confounding damage effects on the mixtures.
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| 17. |
- Birgisson, Björn, et al.
(författare)
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Evaluation of a predicted dynamic modulus for Florida mixtures
- 2005
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Ingår i: Transportation Research Record. - 0361-1981 .- 2169-4052. ; :1929, s. 200-207
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Tidskriftsartikel (refereegranskat)abstract
- The new 2002 AASHTO guide for the design of pavement structures is based on mechanistic principles and requires the dynamic modulus as input to compute stress, strain, and rutting and cracking damage in flexible pavements. The 2002 AASHTO guide has three different levels of analysis; the level used depends on the importance of the pavement structure in question. Dynamic modulus testing is required for Level 1 pavement analysis, whereas no laboratory test data are required for Level 2 and Level 3 pavement analysis. Instead, a predictive dynamic modulus equation is used to generate input values. It is of significant importance to state agencies to understand how well the dynamic modulus for locally available materials compares with the predicted dynamic modulus. This paper presents the results of a study by the Florida Department of Transportation and the University of Florida that focused on the evaluation of the dynamic modulus predictive equation used in the new AASHTO 2002 guide for mixtures typical to Florida. The resulting research program consisted of dynamic modulus testing of 28 mixtures common to Florida. Results showed that on average the predictive modulus equation used in the new AASHTO 2002 flexible pavement design guide appeared to work well for Florida mixtures when used with a multiptier to account for the uniqueness of local mixtures. Results of the study also identified optimal viscosity-temperature relationships that result in the closest correspondence between measured and predicted dynamic modulus values.
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| 18. |
- Birgisson, Björn, et al.
(författare)
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Evaluation of Gradation Effects on Dynamic Modulus
- 2005
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Ingår i: Transportation Research Record. - 0361-1981 .- 2169-4052. ; :1929, s. 193-199
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Tidskriftsartikel (refereegranskat)abstract
- The importance of aggregate characteristics has been emphasized in the Superpave (R) asphalt mixture design procedure. However, criteria for guidelines for the selection of suitable aggregate gradations-other than gradation limits for different nominal maximum size aggregate blends, including the restricted zone-have been neglected. With the move toward mechanistic-empirical pavement design, the dynamic modulus is used to account for mixture properties in the pavement design. It is of significant importance to mix designers to possess a framework for determining how to optimize a mixture for ensuring an adequate dynamic modulus. This paper presents the results from a study of the effects of gradation characteristics on the dynamic modulus. Power law-based gradation factors are obtained for 13 aggregate gradations (coarse and fine graded) composed of limestone and granite aggregates. These gradation factors were used to identify and evaluate relationships between gradation factors and the dynamic modulus at higher temperature (40 degrees C). Subsequently, a tentative framework was established for optimizing mixture gradations for dynamic modulus values. Findings illustrate that gradation factors based on power law parameters can be used to optimize mixture gradations for key mixture properties, such as the dynamic modulus. Results also demonstrate the critical nature of aggregate gradation in achieving desired mixture properties.
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| 19. |
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| 20. |
- Birgisson, Björn, et al.
(författare)
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Performance-based fracture criterion for evaluation of moisture susceptibility in hot-mix asphalt
- 2004
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Ingår i: Transportation Research Record. - 0361-1981 .- 2169-4052. ; :1891, s. 55-61
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Tidskriftsartikel (refereegranskat)abstract
- The laboratory testing procedures currently available for testing hot-mix asphalt moisture susceptibility all evaluate the effects of moisture damage in the laboratory by measuring the relative change of a single parameter before and after conditioning (i.e., tensile strength ratio, resilient modulus ratio). The use of a single parameter to evaluate moisture damage must be questioned. Instead, a single unified framework that accounts for changes in key mixture properties is needed to evaluate the effects of moisture damage in mixtures effectively. The use of a new performance-based fracture parameter, the energy ratio (ER), for quantifying the effects of moisture damage on the fracture resistance of mixtures is evaluated here. ER is used to determine the effects of moisture damage on changes in the fracture resistance of six granite mixtures prepared with and without the use of an antistripping additive. The granite aggregate used is a known stripping aggregate. In addition, one limestone mixture with a known high resistance to stripping was used. The results indicate that not only is the ER capable of detecting the effects of moisture damage on the fracture resistance of mixtures, it is also shown to detect the presence of antistripping agents in mixtures. Results indicate that the ER may form the basis of a promising combined performance-based fracture criterion for evaluating the effects of moisture damage in mixtures as well as the overall resistance to fracture.
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| 21. |
- Buasiri, Thanyarat, et al.
(författare)
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Role of Carbon Nanofiber on the Electrical Resistivity of Mortar under Compressive Load
- 2021
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Ingår i: Transportation Research Record. - : Sage Publications. - 0361-1981 .- 2169-4052. ; 2675:9, s. 32-37
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Tidskriftsartikel (refereegranskat)abstract
- A nanomodified cement consisting of particles with in situ synthesized carbon nanofibers was developed to introduce a strong load-sensing capability of the hydrated binder matrix. The material was produced using chemical vapor deposition. The nanomodified cement contained 2.71 wt% of carbon nanofibers (CNFs). The electrical properties of the composite were determined. Several mortar samples were prepared by partially substituting ordinary Portland cement with 2, 4, 6, 8, and 10 wt% of the nanomodified cement. Additionally an ordinary Portland cement mortar was used as reference. The results show that the strongest piezoresistive response and therefore the best load-sensing was obtained for the mortar containing the highest amount of CNFs. This mortar contained 10 wt% of nanomodified cement. The fractional change in electrical resistivity of this mortar was 82% and this mortar had a compressive strength of 28 MPa.
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| 22. |
- Bullough, J. D., et al.
(författare)
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Work zone lighting and visual performance : Analysis and Demonstration
- 2013
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2337, s. 25-34
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Tidskriftsartikel (refereegranskat)abstract
- In part because of the potential for high levels of glare from work zone illumination, recommendations for light levels from work zone illumination systems are substantially higher than for levels used along roadways in non-work zone locations. In a two-part study, requirements for work zone illumination light levels were assessed. First, levels for workers varying in age from 20 to 60 years were evaluated with the relative visual performance model, with and without the presence of visibility-reducing glare. Except for the smallest, lowest-contrast tasks performed by the older workers, an illuminance of 10 lx resulted in visibility well above the threshold even in the presence of glare, and an illuminance of 30 lx resulted in suprathreshold visibility for these conditions as well. The results of these computational analyses were largely confirmed in a full-scale, outdoor field demonstration attended by transportation agency engineers and highway contractors. Together, the findings suggest that when lighting systems provide sufficient glare control, light levels do not always need to be especially high to ensure adequate visibility for workers.
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| 23. |
- Burghout, Wilco, et al.
(författare)
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Hybrid Mesoscopic-Microscopic Traffic Simulation
- 2005
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Ingår i: Transportation Research Record. - 0361-1981 .- 2169-4052. ; 1934, s. 218-225
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Tidskriftsartikel (refereegranskat)abstract
- Traffic simulation is an important tool for modeling the operations of dynamic traffic systems. Although microscopic simulation models provide a detailed representation of the traffic process, macroscopic and mesoscopic models capture the traffic dynamics of large networks in less detail but without the problems of application and calibration of microscopic models. This paper presents a hybrid mesoscopic-microscopic model that applies microscopic simulation to areas of specific interest while simulating a large surrounding network in less detail with a mesoscopic model. The requirements that are important for a hybrid model to be consistent across the models at different levels of detail are identified. These requirements vary from the network and route choice consistency to the consistency of the traffic dynamics at the boundaries of the microscopic and mesoscopic submodels. An integration framework that satisfies these requirements is proposed. A prototype hybrid model is used to demonstrate the application of the integration framework and the solution of the various integration issues. The hybrid model integrates MlTSIMLab, a microscopic traffic simulation model, and Mezzo, a newly developed mesoscopic model. The hybrid model is applied in two case studies. The results are promising and support both the proposed architecture and the importance of integrating microscopic and mesoscopic models.
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| 24. |
- Burghout, Wilco, et al.
(författare)
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Hybrid traffic simulation with adaptive signal control
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :1999, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid mesoscopic-microscopic model is implemented that applies microscopic simulation to areas of specific interest while simulating a large surrounding network in lesser detail with a mesoscopic model. The hybrid model integrates VisSim, a microscopic traffic simulation model, and Mezzo, a recently developed mesoscopic model. The hybrid model is applied on a network in which Mezzo simulates the entire area (6,000 links) of Stockholm, Sweden, and VisSim simulates the area of specific interest, containing three intersections with adaptive signal control with bus-priority functions. The adaptive signal control and bus-priority functions are simulated by a separate signal controller simulator (EC-1 simulator) that interacts with the hybrid Mezzo-VisSim model and thereby provides the actual signal changes that would take place in the field. Two alternative control schemes are evaluated with the hybrid setup: the original fixed-time control and the new adaptive control. The results show clear improvement in terms of travel times, delays, and stops with the new adaptive control scheme. They also show that although these improvements for the local (microlevel) area attract additional traffic from the surrounding (mesolevel) area, the net effects both locally and networkwide remain positive in terms of travel times, average number of stops, and delay. Moreover, this study demonstrates the advantages of hybrid simulation in evaluation of complicated adaptive traffic control in which both local detailed effects and network effects need to be studied.
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| 25. |
- Burghout, Wilco, et al.
(författare)
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Incident Management and Traffic Information Tools and Methods for Simulation-Based Traffic Prediction
- 2010
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2161, s. 20-28
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Tidskriftsartikel (refereegranskat)abstract
- Incident response and mitigation are among the main tasks of operators at traffic control centers. Simulation models have a good chance of reproducing and predicting the effects of incident response by explicitly modeling driver response to the incident and information provided. In the PREDIKT project sponsored by the Swedish National Road Administration, the state-of-the-art mesoscopic simulation model MEZZO was extended to provide decision support for incident management. Numerous essential modeling components are described and tested, including modeling the incident response logic, a mixed-logit model, and a method for generating alternatives for drivers switching routes. In addition, the results of a fast calibration method based on simultaneous perturbation statistic approximation are presented. The model components are tested in a small case study that investigates the effect of delay in providing information to drivers after incidents. A linearization of speed-density functions also is shown to improve computational performance by 30% and increase calibration speed and stability while preserving simulation accuracy.
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| 26. |
- Börjesson, Maria, 1974-, et al.
(författare)
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Within-Individual Variation in Preferences Equity Effects of Congestion Charges
- 2013
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2382, s. 92-101
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this research was to explore how the values of travel time (VTT) and preferences for different modes vary within individuals compared with the variation between observed trips. With 6-week revealed preference panel data and stated preference data from a mode choice context, both collected in Switzerland, a revealed stated preference logit mode choice model was estimated. The model was applied to simulate how VTT and change in consumer surplus vary across trips within and between individuals over the 6 weeks in response to a hypothetical congestion-charging scheme. The variation in VTT arising from income differences was found to be substantially smaller than the variation in VTT between trips. Moreover, the variability in VTT averaged over all trips within each individual was considerably smaller than the variability in VTT for all observed trips. Therefore, the assumption that variation in VTT between observed trips reflects the variation in the average VTT between individuals, which is usually made in equity analyses, will over-state the between-individual variation. The results suggest that if intraindividual variation in preferences is not taken into account, the negative equity effects of congestion charges are likely to be overestimated.
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| 27. |
- Castrellon, Juan Pablo, 1989, et al.
(författare)
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Enabling Factors and Durations Data Analytics for Dynamic Freight Parking Limits
- 2023
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; 2677:2, s. 219-234
-
Tidskriftsartikel (refereegranskat)abstract
- Freight parking operations occur amid conflicting conditions of public space scarcity, competition with other users, and the inefficient management of loading zones (LZ) at cities’ curbside. The dynamic nature of freight operations, and the static LZ provision and regulation, accentuate these conflicting conditions at specific peak times. This generates supply–demand mismatches of parking infrastructure. These mismatches have motivated the development of Smart LZ that bring together technology, parking infrastructure, and data analytics to allocate space and define dynamic duration limits based on users’ needs. Although the dynamic duration limits unlock the possibility of a responsive LZ management, there is a narrow understanding of factors and analytical tools that support their definition. Therefore, the aim of this paper is twofold. Firstly, to identify factors for enabling dynamic parking durations policies. Secondly, to assess data analytics tools that estimate freight parking durations and LZ occupation levels based on operational and locational features. Semi-structured interviews and focus group analyses showed that public space use assessment, parking demand estimation, enforcement capabilities, and data sharing strategies are the most relevant factors when defining dynamic parking limits. This paper used quantitative models to assess different analytical tools that study LZ occupation and parking durations using tracked freight parking data from the City of Vic (Spain). CatBoost outperformed other machine learning (ML) algorithms and queuing models in estimating LZ occupation and parking durations. This paper contributes to the freight parking field by understanding how data analytics support dynamic parking limits definition, enabling responsive curbside management.
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| 28. |
- Cats, Oded, et al.
(författare)
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Bus-Holding Control Strategies Simulation-Based Evaluation and Guidelines for Implementation
- 2012
-
Ingår i: Transportation Research Record. - : National Academy of Sciences. - 0361-1981 .- 2169-4052. ; :2274, s. 100-108
-
Tidskriftsartikel (refereegranskat)abstract
- Transit operations involve several inherent sources of uncertainty, including dispatch time from the origin terminal, travel time between stops, and dwell time at stops. Bus-holding control strategies are a prominent method applied by transit operators to improve transit performance and level of service. The common practice is to regulate departures from a limited number of stops by holding buses until their scheduled departure time. An analysis of the performance of a high-frequency bus line in Stockholm, Sweden, based on automatic vehicle location data showed that this control strategy was not effective in improving service regularity along the line. The analysis also indicated that drivers adjusted their speed according to performance objectives. Implications of a control strategy that regulates departures from all stops on the basis of the headways of the preceding bus and the following bus were evaluated with Bus Mezzo, a transit operations simulation model. The results suggest that this strategy can improve service performance considerably from both passengers' and operator's perspectives. In addition, the strategy implies cooperative operations, as the decisions of each driver are interdependent with other drivers' decisions, and mutual corrections can be made. Difficulties in realizing the benefits of the proposed strategy in practice, such as dispatching from the origin terminal, driver scheduling, and compliance, are discussed. The implications of several practical considerations are assessed by conducting a sensitivity analysis as part of the preparations for a field experiment designed to test the proposed control strategy.
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| 29. |
- Cats, Oded, et al.
(författare)
-
Effect of real-time transit information on dynamic passenger path choice.
- 2011
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981. ; 2217, s. 46-54
-
Tidskriftsartikel (refereegranskat)abstract
- Real-time information is increasingly being implemented in transit networks worldwide. The evaluation of the effect of real-time information requires dynamic modeling of transit operations and of passenger path choices. This paper presents a dynamic transit analysis and evaluation tool that represents time-tables, operation strategies, real-time information, adaptive passenger choices, and traffic dynamics at the network level. Transit path choices are modeled as a sequence of boarding, walking and alighting decisions that passengers undertake when carrying out their journey. The model is applied to the Metro network of Stockholm, Sweden area under various operating conditions and information provision scenarios, as a proof of concept. An analysis of the results indicates substantial path choice shifts and potential time savings associated with more comprehensive real-time information provision and transfer coordination improvements.
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| 30. |
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| 31. |
- Cats, Oded, et al.
(författare)
-
Evolution of Satisfaction with Public Transport and Its Determinants in Sweden Identifying Priority Areas
- 2015
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2538, s. 86-95
-
Tidskriftsartikel (refereegranskat)abstract
- Measuring and analysing satisfaction with public transport services facilitates service performance monitoring, market analysis, benchmarking and the identification of priority areas. The systematic and regular collection of information concerning satisfaction enables to investigate how passengers’ satisfaction as well as its determinants changes over time. These changes may be driven by changes in service quality or shifts in passengers’ expectations and preferences. This study analyses how satisfaction with public transport and its determinants evolved over time in Sweden in the years 2001-2013. The determinants of satisfaction are identified based on a factor analysis and the estimation of multivariate satisfaction models. The superposition of our findings culminates in a dynamic passenger satisfaction priority map which allows identifying priority areas based on observed trends in satisfaction with service attributes and their respective importance. The deterioration of overall satisfaction with public transport in Sweden in recent years is driven by a decrease in satisfaction with customer interface and length of trip time. These two service aspects as well as operation were found key determinants of overall satisfaction which users consistently rate among the least satisfactory. The results of this study are instrumental in supporting service providers in designing measures that will foster satisfaction in the future.
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| 32. |
- Cats, Oded, et al.
(författare)
-
Impacts of holding control strategies on transit performance : A bus simulation model analysis
- 2011
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2216, s. 51-58
-
Tidskriftsartikel (refereegranskat)abstract
- Transit operators are interested in strategies to improve service reliability as it is an important measure of performance and level of service. One of the common practices aimed at reducing service unreliability is holding control strategies. The design of these strategies involves the selection of a set of time point stops and the holding criteria for regulating the departure time. The interactions between passenger activity, transit operations, and traffic dynamics must be dynamically modeled to analyze the impacts of holding strategies on transit performance. An evaluation of different holding criteria and the number and location of time point stops was conducted with Bus Mezzo, a dynamic transit simulation model. The holding strategies were implemented in the model and applied to a high-frequency trunk bus line in Stockholm, Sweden. The analysis of the results considers the implications of holding strategies from both passenger and operator perspectives. The analysis suggests substantial gains are possible by implementing a holding strategy on the basis of the mean headway from the preceding and the succeeding buses. This strategy is the most efficient for passenger time savings as well as fleet costs and crew management.
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| 33. |
- Cats, Oded, 1983-, et al.
(författare)
-
Learning and adaptation in dynamic transit assignment models for congested networks
- 2020
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; 2674:1, s. 113-124
-
Tidskriftsartikel (refereegranskat)abstract
- The distribution of passenger demand over the transit network is forecasted using transit assignment models which conventionally assume that passenger loads satisfy network equilibrium conditions. The approach taken in this study is to model transit path choice as a within-day dynamic process influenced by network state variation and real-time information. The iterative network loading process leading to steady-state conditions is performed by means of day-to-day learning implemented in an agent-based simulation model. We explicitly account for adaptation and learning in relation to service uncertainty, on-board crowding and information provision in the context of congested transit networks. This study thus combines the underlying assignment principles that govern transit assignment models and the disaggregate demand modeling enabled by agent-based simulation modeling. The model is applied to a toy network for illustration purposes, followed by a demonstration for the rapid transit network of Stockholm, Sweden. A full-scale application of the proposed model shows the day-to-day travel time and crowding development for different levels of network saturation and when deploying different levels of information availability.
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| 34. |
- Cats, Oded, et al.
(författare)
-
Mesoscopic Modeling of Bus Public Transportation
- 2010
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2188, s. 9-18
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of public transport system performance and level of service in urban areas is essential. Dynamic modeling of traffic conditions, passenger demand, and transit operations is important to represent adequately the complexity of and the interactions between these components in modern public transportation systems. This paper presents a transit simulation model designed to support evaluation of operations planning and control, especially in the context of advanced public transportation systems. Unlike most previous efforts in this area, the simulation model is built on a platform of a mesoscopic traffic simulation model, which allows modeling or the operation dynamics of large-scale transit systems, taking into account the main sources of service uncertainty and stochasticity. The capabilities of Mezzo as an evaluation tool of transit operations are demonstrated with an application to a real-world, high-demand bus line in metropolitan Tel Aviv, Israel, under various scenarios. The application shows that important phenomena such as bus bunching are reproduced realistically. A comparison of simulated running times and headway distributions with field data shows the model is capable of replicating observed data.
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| 35. |
- Cats, Oded, et al.
(författare)
-
Public Transport Pricing Policy Empirical Evidence from a Fare-Free Scheme in Tallinn, Estonia
- 2014
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2415, s. 89-96
-
Tidskriftsartikel (refereegranskat)abstract
- Cities worldwide are looking for new policies to attract travelers to shift from cars to public transport. Policies focused on reducing public transport fares are aimed at improving social inclusion and leading to a modal shift. The City of Tallinn, the capital of Estonia, has recently introduced a fare-free public transport (FFPT) service in an effort to improve accessibility and mobility for its residents. The case of Tallinn is a full-scale, real-world experiment that provides a unique opportunity for investigating the impacts of FFPT policy. A macrolevel empirical evaluation of FFPT impacts on service performance, passenger demand, and accessibility for various groups of travelers is presented. In contrast to previous studies, the influence of FFPT on passenger demand was estimated while changes in supply were controlled. The results indicate that the FFPT measure accounts for an increase of 1.2% in passenger demand, with the remaining increase attributed to an extended network of public transport priority lanes and increased service frequency. The relatively small effect could be attributed to the previous price level and public transport share as well as analysis of the short-term impact. The evidence-based policy evaluation in this paper is instrumental in supporting policy making and facilitating the design of public transport pricing strategies.
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| 36. |
- Chen, Feng, et al.
(författare)
-
Potential Influences on Long-Term Service Performance of Road Infrastructure by Automated Vehicles
- 2016
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2550, s. 72-79
-
Tidskriftsartikel (refereegranskat)abstract
- Automated vehicles (AVs) have received great attention in recent years, and an automated road transportation sector may become reality in the next decades. Many benefits of AVs have been optimistically predicted, although some benefits may be overestimated because of a lack of thinking from a holistic point of view. From a future perspective, this study investigated the potential consequences to the long-term service performance of practical physical road infrastructure after the advent of the implementation of AVs on a large scale. Specifically, the, pavement rutting performance by the possibly changed behaviors, such as the vehicle's wheel wander, lane capacity, and traffic speed, was examined carefully with the finite element modeling approach. With the use of AVs, the decreased wheel wander and increased lane capacity could bring an accelerated rutting potential, but the increase in traffic speed would negate this effect, which was shown by the simulation results of rut depth. Therefore the influence cannot be judged as positive or negative in general; judgment actually depends much on the practical road and traffic conditions. In the future the physical roads not only might serve for the mobility of the vehicles but also might be capable of enabling other new functions. An early consideration of how to lead the future development of physical road infrastructure toward multifunctionality is emphasized.
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| 37. |
- Chen, M., et al.
(författare)
-
Service evaluation of public bicycle scheme from a user perspective
- 2017
-
Ingår i: Transportation Research Record. - : National Research Council. - 0361-1981 .- 2169-4052. ; 2634, s. 28-34
-
Tidskriftsartikel (refereegranskat)abstract
- In late 2005, in an attempt to solve the last-mile problem, China started implementing public bikesharing programs. The effort quickly grew to a massive scale. An estimated 400,000 public bicycles now are in use in China, which is more than in all other countries that have implemented public bicycle schemes (PBSs). As with any emerging service that develops rapidly, an understanding of user behavior and satisfaction is lacking. Factors that influence the frequency of public bicycle use were studied in Hangzhou, China. Online and intercept surveys were conducted with PBS users. Willingness to use the PBS as well as satisfaction with and concerns about the PBS were investigated. Analysis of variance was conducted to identify the six factors that affect a user's decision to rent: car ownership, bicycle ownership, travel purpose, having or lacking familiarity with the rental process, level of satisfaction with the PBS, and level of familiarity with the distribution of docking stations. Binary logistic regression analysis was used to elucidate details of key factors in the group of most frequent users-that is, survey respondents who did not own a car, rented a bicycle primarily for shopping or going out for business, and were familiar with the rental process and the distribution of docking stations. Based on study findings, advice is presented for implementing policy in developing countries. Suggestions include publicizing the PBS more, attracting more commuters to bicycling to reduce congestion, enhancing the accessibility of docking stations to accommodate more potential users, and improving bicycle quality to encourage more participation and make it easier for elderly citizens to participate.
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| 38. |
- Chen, X., et al.
(författare)
-
Unplanned Disruption Analysis and Impact Modeling in Urban Railway Systems
- 2022
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; 2676:10, s. 16-27
-
Tidskriftsartikel (refereegranskat)abstract
- Unplanned disruptions bring challenges to urban railway system operations because of their impacts on safety, operation efficiency, and service quality. Identifying the contributing factors of operation delays and affected areas under unplanned disruptions is critical for agencies to make effective and informed management decisions. Despite its importance, few studies have been reported on unplanned disruption analysis in urban railway systems or they have been limited in their analysis and modeling because of the lack of disruption data. This paper collects a complete set of unplanned disruption data for 7 years in Hong Kong and explores important factors affecting operation delays and affected areas. Quantile regression (QR) models are developed to explore the causes of operation delays under unplanned disruptions. The significant factors include the time of day, weather condition, signal control system (moving/fixed block), line types (urban/suburban), line operation direction, disruption location (underground/ground/elevated), the number of affected stations, and disruption types (e.g., tracing, locomotive and rolling stock, passengers, and operation). A binary logit model is developed to explore the variables contributing to the affected areas (single or multiple stations). The results show that the affected area is significantly influenced by the signal control system, line types, line operation direction, disruption location, terminal/departure station involved or not, transfer station involved or not, and disruption types. The findings provide useful insights into unplanned disruptions and support the development of engineering and policy countermeasures to prevent and mitigate unplanned disruption effects on operations and services.
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| 39. |
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| 40. |
- Chowdhury, Subeh, et al.
(författare)
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Formation of Fear and Adaptive Behavior in Young Ethnic Minority Women Riding Public Transport
- 2023
-
Ingår i: Transportation Research Record. - : Sage Publications. - 0361-1981 .- 2169-4052. ; , s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- oung ethnic minority women face unique challenges when riding public transport. The present study contributes by providing a narrative-based examination of young ethnic minority women’s formation of fear and adaptive behavior when using public transport. Twenty-nine ethnic minority women, under the age of 30, participated in a semi-structured interview inAuckland, New Zealand. Findings show that adaptive behavior commonly includes pre-planning nighttime trips, relying ontheir phones to act confident and engage in communication with family en-route, and appearing disinterested to reduceunwanted attention. These measures are expressions of women’s agency and their capacity to prevent victimization and manage fear, particularly in places where they feel unsafe, such as empty stations and dark or enclosed environments. Their livedexperiences highlight the level of anxiety they experience on a regular basis. Participants discussed how they are acutelyaware of their ethnicity (and appearance) when using public transport at all times of the day. They remain near exits and areconstantly on high alert. They also discussed how, from an early age, women are educated in a culture of ‘‘stranger-danger’’which in the long term erodes their confidence to travel independently and safely. These findings show that the currentdesign of public transport systems does not adequately meet the travel needs of certain groups of women. Public transportauthorities are encouraged to gain deeper insights into these issues and develop design strategies which promoteinclusiveness
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| 41. |
- Dinegdae, Yared H., et al.
(författare)
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Reliability-Based Design Procedure for Fatigue Cracking in Asphalt Pavements
- 2016
-
Ingår i: Transportation Research Record. - : NATL ACAD SCIENCES. - 0361-1981 .- 2169-4052. ; :2583, s. 127-133
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Tidskriftsartikel (refereegranskat)abstract
- The need to account for the effect of design input variabilities on predicted performance has led to many design procedures that address reliability for pavement applications. The Florida cracking model uses empirically derived reliability for fatigue cracking design of asphalt pavements. A reliability approach, which is based on probabilistic uncertainty quantification, is necessary to account properly and effectively for the contribution of the variability in each parameter to the overall variance. This paper presents a load and resistance factor design (LRFD) procedure for the Florida cracking model. By delivering designs of uniform reliability, LRFD provides the basis for developing quality control and quality assurance standards. A first-order reliability method that incorporates a surrogate model based on central composite design was used to compute the reliability and formulate the partial safety factors. The reliability calibration was based on field pavement sections that had a wide range of design inputs and target reliability. Illustrative designs based on the developed LRFD procedure show the effectiveness of the partial safety factors and further confirm the credibility of the reliability analysis methodology.
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| 42. |
- Dinegdae, Yared, 1981-, et al.
(författare)
-
Toward a Comprehensive Pavement Reliability Analysis Approach
- 2023
-
Ingår i: Transportation Research Record. - : Sage Publications. - 0361-1981 .- 2169-4052. ; 2677:7, s. 680-692
-
Tidskriftsartikel (refereegranskat)abstract
- Reliability has been incorporated in pavement design tools to account for input variability influence on predicted performance. As they are not based on a probabilistic method of uncertainty propagation, the reliability analysis methodologies that are currently implemented in pavement performance tools lack rigor and robustness. This paper investigates the potential of three reliability analysis methodologies for pavement application: the Pavement ME reliability analysis methodology, Monte Carlo simulation (MCS), and the first-order reliability method (FORM). The MCS and FORM involve a response surface method for the generation of a second-order surrogate model. The investigation was performed using inputs and performance data from accelerated pavement testing structures. Inputs that were identified as significant were characterized as random variables and their associated variability was established using measured structural and material properties. Pavement performance with respect to rutting was predicted using the ERAPave performance prediction tool, while MCS was used to generate the actual variability of the distress. The reliability analysis results have shown that a comprehensive reliability analysis methodology is required that effectively captures input variabilities and the error associated with surrogate models.
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| 43. |
- Ding, Jing, et al.
(författare)
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Routing Policy Choice Set Generation in Stochastic Time-Dependent Networks Case Studies for Stockholm, Sweden, and Singapore
- 2014
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2466, s. 76-86
-
Tidskriftsartikel (refereegranskat)abstract
- Transportation systems are inherently uncertain because of random disruptions; nevertheless, real-time information can help travelers make better route choices under such disruptions. The first revealed-preference study of routing policy choice is presented. A "routing policy" is defined as a decision rule applied at each link that maps possible realized traffic conditions to decisions to be made on the link next. The policy represents a traveler's ability to incorporate real-time information not yet available at the time of decision. Two case studies are conducted in Stockholm, Sweden, and in Singapore. Data for the underlying stochastic time-dependent network are generated from taxi GPS traces through map-matching and nonparametric link travel time estimation. An efficient algorithm to find the optimal touting policy in large-scale networks is first presented, which is a building block of any routing policy choice set generation method. The routing policy choice sets are then generated by link elimination and simulation. The generated choice sets are first evaluated on the basis of whether they include the observed traces on a specific day, or coverage. The sets are then evaluated on the basis of "adaptiveness," defined as the capability of a routing policy to be realized as different paths over different days. A combination of link elimination and simulation methods yields satisfactory coverage. The comparison with a path choice set benchmark also suggests that a routing policy choice set could potentially provide better coverage and capture the adaptive nature of route choice.
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| 44. |
- Engelson, Leonid
(författare)
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Properties of Expected Travel Cost Function with Uncertain Travel Time
- 2011
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2254, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a theoretical analysis of travelers' scheduling preferences and the resulting form of the expected utility that includes travel time reliability measures. A series of research papers and reports used the mean standard deviation approach to evaluate policies that improve travel time reliability. Recently, this approach was theoretically substantiated under the conventional assumptions of constant marginal utility of time (MUT) at the origin, two discrete MUT values at the destination, and constant standardized travel time distribution. In this paper, properties of the minimal expected travel cost are investigated with smooth MUTs at the origin and destination of the trip. The influence of small variations in travel time on travel cost is well approximated by a term proportional to the travel time variance and independent of the distribution form of travel time. Two examples of MUT functions are provided: the minimal expected travel cost can be analytically expressed through moments or through a moment generating function of travel time, and conditions are stated guaranteeing that the expected travel cost is exactly additive by independent parts of the trip. These results provide justification in particular for the mean variance approach to modeling drivers' decisions under uncertain travel times. This formulation is convenient especially for scheme evaluation in large road networks because it allows the use of conventional network assignment routines by just modifying the volume delay functions to include the travel time variability term.
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| 45. |
- Engholm, Albin, 1991-, et al.
(författare)
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Cost Analysis of Driverless Truck Operations
- 2020
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052.
-
Tidskriftsartikel (refereegranskat)abstract
- Road freight transport is believed by many to be the first transport domain in which driverless (DL) vehicles will have a significant impact. However, in current literature almost no attention has been given to how the diffusion of DL trucks might occur and how it might affect the transport system. To make predictions on the market uptake and to model impacts of DL truck deployment, valid cost estimates of DL truck operations are crucial. In this paper, an analysis of costs and cost structures for DL truck operations, including indicative numerical cost estimates, is presented. The total cost of ownership for DL trucks compared with that for manually driven (MD) trucks has been analyzed for four different truck types (16-, 24-, 40-, and 64-ton trucks), for three scenarios reflecting pessimistic, intermediate, and optimistic assumptions on economic impacts of driving automation based on current literature. The results indicate that DL trucks may enable substantial cost savings compared with the MD truck baseline. In the base (intermediate) scenario, costs per 1,000 ton-kilometer decrease by 45%, 37%, 33%, and 29% for 16-, 24-, 40-, and 60-ton trucks, respectively. The findings confirm the established view in the literature that freight transport is a highly attractive area for DL vehicles because of the potential economic benefits.
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| 46. |
- Erlingsson, Sigurdur, et al.
(författare)
-
Evaluation of Permanent Deformation Characteristics of Unbound Granular Materials by Means of Multistage Repeated-Load Triaxial Tests
- 2013
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2369, s. 11-19
-
Tidskriftsartikel (refereegranskat)abstract
- Rutting in flexible pavements is often associated with permanent deformation of the unbound granular layer. The current permanent deformation models are applicable only to a single stress path in repeated-load triaxial (RLT) tests, in which the load pulses are of constant amplitude. In this paper, a general approach using the time-hardening concept was introduced to model the permanent deformation of unbound granular materials (UGMs) continuously in multistage (MS) RLT tests, in which load pulses of a range of different amplitudes are applied, to represent field conditions realistically. With this formulation, three existing permanent deformation models were reconstructed, and one of the models was slightly modified, to suit MS loading conditions better. The material parameters of these models were then optimized for three UGMs used in pavement construction with data from MS RLT tests and application of a least squares curve-fitting method to the test data. The goodness-of-fit statistics were computed to evaluate and compare the quality of fit achieved with these models. The shakedown ranges were also calculated for each stress path of the MS RLT tests to compare these models in simulating these ranges. Generally, the time-hardening approach, for which the quality of fit is dependent on the chosen model, was found to work successfully. In this study, the selected models performed quite well, with the modified model showing the closest agreement to the test data. Thus, this approach has the potential to be applied for better modeling and prediction of pavement performance.
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| 47. |
- Erlingsson, Sigurdur, et al.
(författare)
-
Evaluation of permanent deformation characteristics of unbound granular materials from multi-stage repeated load triaxial test
- 2013
-
Ingår i: Transportation Research Record. - : Sage Publications. - 0361-1981 .- 2169-4052. ; 2369:1, s. 11-19
-
Tidskriftsartikel (refereegranskat)abstract
- Rutting in flexible pavements is often associated with permanent deformation of the unbound granular layer. The current permanent deformation models are only applicable to a single stress path in repeated load triaxial (RLT) tests. In this paper, a simple approach using the time hardening concept was introduced to continuously model the permanent deformation of unbound granular materials (UGM) in multi-stage (MS) repeated load triaxial (RLT) tests. Three existing permanent deformation models were reconstructed to be implemented with this method and one model was slightly modified to better suit this approach. This approach was validated by calibrating these reconstructed models using data from MS RLT tests on three different UGM used in base layers of flexible pavement structures. The calibrations were done by optimizing the material parameters of the models using least square curve fitting method. The shakedown ranges were also calculated for each stress path of the MS RLT tests to compare these models in simulating these ranges. Generally, very good fits were obtained for these models where the modified model showed the best agreement.
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| 48. |
- Farah, Haneen
(författare)
-
Age and Gender Differences in Overtaking Maneuvers on Two-Lane Rural Highways
- 2011
-
Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2248, s. 30-36
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Tidskriftsartikel (refereegranskat)abstract
- For decades researchers have been pointing out significant differences in the driving behavior between young and old and between male and female drivers. There are many studies concerning age and gender differences in risk perception, traffic accident involvement, traffic violations, alcohol consumption, and risky driving. However, little effort has been focused on studying the behavioral differences in overtaking maneuvers on two-lane highways. A considerable percentage of the fatal accidents on two-lane highways is directly related to overtaking maneuvers. Therefore, the main focus of this study is to understand better the overtaking behavior of different drivers classified by their age and gender. Data on the overtaking behavior of 100 drivers were collected with an interactive driving simulator. Several scenarios of two-lane rural highways with different geometric and traffic conditions were developed. The results show interesting and significant differences in the overtaking behavior of drivers depending on their age and gender. These differences are mainly in the frequency of overtaking maneuvers, overtaking time duration, following distances, critical overtaking gaps, and desired driving speeds. Geometric and traffic conditions were also found to have a significant impact on drivers' overtaking behavior. The findings of this study contribute to the understanding of the overtaking behavior of different groups of drivers and thus have implications for road safety intervention programs and the development of effective risk reduction strategies adapted and targeted for different age and gender groups.
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| 49. |
- Forsman, Åsa, et al.
(författare)
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Impact of nonresponse and weighting in Swedish travel survey
- 2007
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Ingår i: Transportation Research Record. - : Sage Publications. - 0361-1981 .- 2169-4052. ; 1993:1, s. 80-88
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Tidskriftsartikel (refereegranskat)abstract
- Results from travel surveys, together with traffic monitoring programs, serve as a basis for policy decisions and evaluations. Correct interpretation of the survey results is therefore of vital importance, and the impact of different sources of error needs to be investigated. This paper presents a study of nonresponse errors in a Swedish travel survey. Survey methodologists have addressed the problem of nonresponse for a long time, and several methods have been developed to reduce possible bias. Particularly common are different weighting methods based on auxiliary information. However, the performance of these techniques is based on how well the chosen auxiliary variables can explain the response behavior. The aims of the present study were to (a) investigate whether the mobility of nonrespondents differs from the mobility of respondents and (b) determine whether weighting reduces possible nonresponse bias. A weighting technique called calibration was used. The travel survey was based on a mail questionnaire, and the response rate was about 53%. Nonrespondents were contacted by telephone and asked a selected number of questions from the original questionnaire. Results show that mobility did differ between respondents and nonrespondents for some of the travel modes. The effect of calibration was generally small and inconsistent; the bias was reduced in some cases and increased in others. Nevertheless, calibration is recommended if procedures for calculating the weights are readily available.
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- Franklin, Joel P., et al.
(författare)
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Travel Time Reliability for Stockholm Roadways Modeling Mean Lateness Factor
- 2009
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2134, s. 106-113
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, there has been an increasing awareness that travel time reliability, apart from expected travel time, is an important component of cost-benefit analysis, especially during congested traffic conditions. A common measure of travel time reliability is standard deviation, and it has been shown that this is a theoretically sound measure under scheduling constraints, provided that the mean lateness factor is known. Hence, in applied cost-benefit analyses, one will need both the standard deviation and the mean lateness factor. These analyses would be particularly simple if the mean lateness were constant across time of day and for different routes chosen. A study was done to explore how the mean lateness varies and how its variations can be approximated. With the use of travel time measurements on individual links, it is shown how mean lateness varies considerably across time and space. It is shown that mean lateness exhibits a time-varying pattern depending on the characteristics of congestion on the link. It is also shown that the location of the link in the network is a significant determinant. The resulting model for mean lateness represents a considerable improvement over existing practice, where the mean lateness is implicitly assumed constant, yet a large portion of its variation remains unexplained. The model is useful for informing future research but is of less value for predicting the mean lateness in broad applied settings.
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