| 1. |
- Flötteröd, Gunnar, et al.
(författare)
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Identifiability and Practical Relevance of Complex Car-Following Models
- 2013
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Ingår i: Traffic and Granular Flow '11. - Berlin, Heidelberg : Springer. - 9783642396687 ; , s. 47-55
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This article looks at car-following models from a deliberately pragmaticperspective: What information about driver behavior can be extracted from a givendata set without more or less speculative assumptions about underlying behaviorallaws? The objective of this exercise is not to invalidate existing models but toobtain a better understanding of how much (complex) model structure can berevealed/validated from real data.
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| 2. |
- Wagner, Peter, et al.
(författare)
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Simplified car-following models
- 2012
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Ingår i: TRB 91th Annual Meeting Compendium of Papers CD-ROM. - Washington DC, USA.
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Konferensbidrag (refereegranskat)
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| 3. |
- Almroth, Andreas, et al.
(författare)
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Further development of SAMPERS and modeling of urban congestion
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The need to more precisely represent the consequences of congestion mitigation policies in urban transport systems calls for replacement of the static equilibrium assignment by DTA in the integrated travel demand and traffic assignment models. Despite of the availability of DTA models and despite of the conceptual clarity of how such integration should take place, only few operational model systems have been developed for large-scale applications. We report on replacement of the static traffic assignment by two different DTAs in the four stage demand model for the Greater Stockholm region: the macroscopic analytic Visum DUE and microscopic simulation Transmodeler. First results show that even without systematic calibration the DTA is in reasonable agreement with observed traffic counts and travel times. The presented experiments did not reveal striking difference between using macroscopic and microscopic assignment package. However, given the clear trend to microscopic modeling and simulation on the travel demand side, the use of micro-simulation-based DTA package appears more natural from system integration perspective.
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| 4. |
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| 5. |
- 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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| 6. |
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| 7. |
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| 8. |
- Corthout, Ruben, et al.
(författare)
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Non-unique flows in macroscopic first-order intersection models
- 2012
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 46:3, s. 343-359
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Tidskriftsartikel (refereegranskat)abstract
- Currently, most intersection models embedded in macroscopic Dynamic Network Loading (DNL) models are not well suited for urban and regional applications. This is so because so-called internal supply constraints, bounding flows due to crossing and merging conflicts inherent to the intersection itself, are missing. This paper discusses the problems that arise upon introducing such constraints. A general framework for the distribution of (internal) supply is adopted, which is based on the definition of priority parameters that describe the strength of each flow in the competition for a particular supply. Using this representation, it is shown that intersection models - with realistic behavioral assumptions, and in simple configurations - can produce non-unique flow patterns under identical boundary conditions. This solution non-uniqueness is thoroughly discussed and approaches on how it can be dealt with are provided. Also, it is revealed that the undesirable model properties are not solved - but rather enhanced - when diverting from a point-like to a spatial modeling approach.
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| 9. |
- Deng, Qichen, 1987-
(författare)
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Heavy-Duty Vehicle Platooning : Modeling and Analysis
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coupled with the growth of world economy, the demand for freight transport has escalated and will continue to do so. As the traffic intensity increases, the pressure on infrastructure, energy usage and environment becomes higher than ever. Meanwhile, the number of traffic accidents is also increasing year by year as a result. Heavy-duty vehicle (HDV) platooning makes a group of HDVs driving closely after each other.It is one potential solution to improve transport efficiency, traffic safety and fuel economy. Even though there have been extensive studies on the platooning system and corresponding fuel saving, some of the research areas, such as coordination strategies of platooning, platoon operations and the impacts of HDV platooning on trafficflow are still left open. Under a futuristic scenario where a large number of HDVswill be operating in one or several platoons on highway, how to group HDVs intoa platoon and how to select spacing policies for HDV platooning are essential forautomobile manufacturers, fleet operators and transport planners. Therefore, theformation strategies and operations of HDV platoons, as well as the impacts of HDVplatooning on traffic flow have to be carefully investigated.This thesis presents contributions to the modeling of HDV platooning and simulationof HDV platoon operations. The focus lies mainly on analytical formulation ofspeed-density relation of mixed traffic flow and development of simulation frameworkfor study of HDV platooning. On the one hand, a three-regime speed-density relationis proposed to describe the mixed traffic flow consisting of HDVs and passengercars. The proposed speed-density relation incorporates percentage of HDVs, trafficdensity and spacing policy of HDV platoons as input variables and delivers aggregatehighway velocity as output. By comparing the traffic throughput of no HDV platooningscenario, grouping HDVs into platoon using constant vehicle spacing policy orconstant time gap policy results in significant improvement in highway capacity. On the other hand, a simulation framework is developed for implementation of differentHDV platoon operations. The platoon formation of two HDVs and disaggregation ofa five-HDV platoon at off-ramp are simulated on a two-lane highway. The simulationoutcomes show that HDV platoon formation is more favorable in light and mediumtraffic; disaggregation of a long HDV platoon at off-ramp improves the averagespeed of passenger vehicles considerably at high traffic flow rate.
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| 10. |
- Djukic, T., et al.
(författare)
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Efficient real time OD matrix estimation based on Principal Component Analysis
- 2012
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Ingår i: Intelligent Transportation Systems (ITSC), 2012 15th International IEEE Conference on. - : IEEE. - 9781467330633 ; , s. 115-121
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Konferensbidrag (refereegranskat)abstract
- In this paper we explore the idea of dimensionality reduction and approximation of OD demand based on principal component analysis (PCA). First, we show how we can apply PCA to linearly transform the high dimensional OD matrices into the lower dimensional space without significant loss of accuracy. Next, we define a new transformed set of variables (demand principal components) that is used to represent the fixed structure of OD matrices in lower dimensional space. We update online these new variables from traffic counts in a novel reduced state space model for real time estimation of OD demand. Through an example we demonstrate the quality improvement of OD estimates using this new formulation and a so-called 'colored' Kalman filter over the standard Kalman filter approach for OD estimation, when correlated measurement noise is accounted due to reduction of variables in state vector.
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| 11. |
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| 12. |
- Farooq, Bilal, et al.
(författare)
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Simulation based population synthesis
- 2013
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 58:SI, s. 243-263
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Tidskriftsartikel (refereegranskat)abstract
- Microsimulation of urban systems evolution requires synthetic population as a key input. Currently, the focus is on treating synthesis as a fitting problem and thus various techniques have been developed, including Iterative Proportional Fitting (IPF) and Combinatorial Optimization based techniques. The key shortcomings of these procedures include: (a) fitting of one contingency table, while there may be other solutions matching the available data (b) due to cloning rather than true synthesis of the population, losing the heterogeneity that may not have been captured in the microdata (c) over reliance on the accuracy of the data to determine the cloning weights (d) poor scalability with respect to the increase in number of attributes of the synthesized agents. In order to overcome these shortcomings, we propose a Markov Chain Monte Carlo (MCMC) simulation based approach. Partial views of the joint distribution of agent's attributes that are available from various data sources can be used to simulate draws from the original distribution. The real population from Swiss census is used to compare the performance of simulation based synthesis with the standard IPF. The standard root mean square error statistics indicated that even the worst case simulation based synthesis (SRMSE = 0.35) outperformed the best case IPF synthesis (SRMSE = 0.64). We also used this methodology to generate the synthetic population for Brussels, Belgium where the data availability was highly limited.
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| 13. |
- Fetiarison, Mamy, et al.
(författare)
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Evaluation of pedestrian data collection methods within a simulation framework
- 2010
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Ingår i: Proceedings of the European Transport Conference.
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Konferensbidrag (refereegranskat)abstract
- The estimation and validation of pedestrian behavioral models requires large amounts of detailedand appropriate data, the collection of which is a costly and time-consuming undertaking.The identification and design of an appropriate data collection method therefore is of great importance,which, however, is an arduous and itself time-consuming task. This article describesa software laboratory that facilitates the design of pedestrian data collection campaigns.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Flötteröd, Gunnar
(författare)
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A search acceleration method for optimization problems with transport simulation constraints
- 2017
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Ingår i: Transportation Research Part B: Methodological. - : Elsevier. - 0191-2615. ; 98, s. 1339-1351
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Tidskriftsartikel (refereegranskat)abstract
- This work contributes to the rapid approximation of solutions to optimization problems that are constrained by iteratively solved transport simulations. Given an objective function, a set of candidate decision variables and a black-box transport simulation that is solved by iteratively attaining a (deterministic or stochastic) equilibrium, the proposed method approximates the best decision variable out of the candidate set without having to run the transport simulation to convergence for every single candidate decision variable. This method can be inserted into a broad class of optimization algorithms or search heuristics that implement the following logic: (i) Create variations of a given, currently best decision variable, (ii) identify one out of these variations as the new currently best decision variable, and (iii) iterate steps (i) and (ii) until no further improvement can be attained. A probabilistic and an asymptotic performance bound are established and exploited in the formulation of an efficient heuristic that is tailored towards tight computational budgets. The efficiency of the method is substantiated through a comprehensive simulation study with a non-trivial road pricing problem. The method is compatible with a broad range of simulators and requires minimal parametrization.
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| 19. |
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| 20. |
- Flötteröd, Gunnar
(författare)
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Bayesian calibration of microscopic travel demand models from traffic counts
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The calibration of microsimulation-based demand models is a difficult problem, and there is no source of information that may be disregarded in this process. This work shows how traffic counts can be consistently incorporated in the calibration. The approach is mathematically sound, computationally efficient, and compatible with typical microsimulation techniques
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| 21. |
- Flötteröd, Gunnar, et al.
(författare)
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Bayesian demand calibration for dynamic traffic simulations
- 2011
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Ingår i: Transportation Science. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0041-1655 .- 1526-5447. ; 45:4, s. 541-561
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Tidskriftsartikel (refereegranskat)abstract
- We present an operational framework for the calibration of demand models for dynamic traffic simulations, where calibration refers to the estimation of a structurally predefined model's parameters from real data. Our focus is on disaggregate simulators that represent every traveler individually. We calibrate, also at an individual level, arbitrary choice dimensions within a Bayesian framework, where the analyst's prior knowledge is represented by the dynamic traffic simulator itself and the measurements are comprised of time-dependent traffic counts. The approach is equally applicable to an equilibrium-based planning model and to a telematics model of spontaneous and imperfectly informed drivers. It is based on consistent mathematical arguments, yet it is applicable in a purely simulation-based environment and, as our experimental results show, is capable of handling large scenarios.
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| 22. |
- Flötteröd, Gunnar, et al.
(författare)
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Behavioral calibration and analysis of a large-scale travel microsimulation
- 2012
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Ingår i: Networks and Spatial Economics. - : Springer Science and Business Media LLC. - 1566-113X .- 1572-9427. ; 12:4, s. 481-502
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Tidskriftsartikel (refereegranskat)abstract
- This article reports on the calibration and analysis of a fully disaggregate (agent-based) transport simulation for the metropolitan area of Zurich. The agent-based simulation goes beyond traditional transport models in that it equilibrates not only route choice but all-day travel behavior, including departure time choice and mode choice. Previous work has shown that the application of a novel calibration technique that adjusts all choice dimensions at once from traffic counts yields cross-validation results that are competitive with any state-of-the-art four-step model. While the previous study aims at a methodological illustration of the calibration method, this work focuses on the real-world scenario, and it elaborates on the usefulness of the obtained results for further demand analysis purposes.
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| 23. |
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| 24. |
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| 25. |
- Flötteröd, Gunnar, et al.
(författare)
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Bidirectional pedestrian fundamental diagram
- 2015
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 71, s. 194-212
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a new model of stationary bidirectional pedestrian flow. Starting out from microscopic first principles, a bidirectional fundamental diagram (FD) is derived that defines direction-specific flow rates as functions of direction-specific densities. The FD yields non-negative and bounded flows and guarantees that the instantaneous density changes that would result from these flows stay bounded between zero and jam density. In its minimal configuration, it uses just as many parameters as a unidirectional triangular FD: maximum walking speed, jam density, a collision avoidance parameter (from which the backward wave speed can be derived). A one-on-one mapping between the parameters guiding uni- and bidirectional pedestrian flows is proposed and both conceptually and empirically justified. Generalizations of the FD that maintain its desirable properties turn out to be straightforward by making its parameters density-dependent. The FD performs very well in comparisons against simulated and real data.
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| 26. |
- Flötteröd, Gunnar
(författare)
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Cadyts : a free calibration tool for dynamic traffic simulations
- 2009
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Ingår i: Proceedings of the Swiss Transport Research Conference (STRC).
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Konferensbidrag (refereegranskat)abstract
- This article reports on the realization and on first applications of the Cadyts (“Calibration ofdynamic traffic simulations”) calibration tool. The presented first version of Cadyts calibratesdisaggregate demand models of dynamic traffic assignment simulators from traffic counts. Thetool is broadly applicable in that it (i) makes only very mild assumptions about the calibratedsimulator’s workings and (ii) allows for various modes of technical interaction with the simulationsoftware. The article provides a both conceptual and technical overview of the tool andexemplary demonstrates its applicability to two different traffic microsimulators.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Flötteröd, Gunnar, et al.
(författare)
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Disaggregate path flow estimation in an iterated DTA microsimulation
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This text describes the first application of a novel path flow and origin/destination(OD) matrix estimator for iterated dynamic traffic assignment (DTA) microsimulations.The presented approach, which operates on a trip-based demand representation,is derived from an agent-based DTA calibration methodology that relies onan activity-based demand model. The objective of this work is to demonstrate thetransferability of the agent-based approach to the more widely used OD matrixbaseddemand representation.The calibration (i) operates at the same disaggregate level as the microsimulationand (ii) has drastic computational advantages over usual OD matrix estimators inthat the demand adjustments are conducted within the iterative loop of the DTAmicrosimulation, which results in a running time of the calibration that is in thesame order of magnitude as a plain simulation. We describe an application ofthis methodology to the trip-based DRACULA microsimulation and present anillustrative example that clarifies its capabilities.
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| 35. |
- Flötteröd, Gunnar, et al.
(författare)
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Disaggregate Path Flow Estimation in an Iterated Dynamic Traffic Assignment Microsimulation
- 2014
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Ingår i: Journal of Intelligent Transportation Systems / Taylor & Francis. - : Informa UK Limited. - 1547-2450 .- 1547-2442. ; 18:2, s. 204-214
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the first application of a novel path flow and origin/destination (OD) matrix estimator for iterated dynamic traffic assignment (DTA) microsimulations. The presented approach, which operates on a trip-based demand representation, is derived from an agent-based DTA calibration methodology that relies on an activity-based demand model (Flotterod, Bierlaire, & Nagel, 2011). The objective of this work is to demonstrate the transferability of the agent-based approach to the more widely used OD matrix-based demand representation. The calibration (i) operates at the same disaggregate level as the microsimulation and (ii) has drastic computational advantages over conventional OD matrix estimators in that the demand adjustments are conducted within the iterative loop of the DTA microsimulation, which results in a running time of the calibration that is in the same order of magnitude as a plain simulation. We describe an application of this methodology to the trip-based DRACULA microsimulation and present an illustrative example that clarifies its capabilities.
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| 36. |
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| 37. |
- Flötteröd, Gunnar
(författare)
-
DTA simulation with reduced number of iterations
- 2018
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Konferensbidrag (refereegranskat)abstract
- An iterated (day-to-day) dynamic traffic assignment (DTA) is considered. In each iteration, a certain fraction of the total travel demand adjusts its travel pattern before the entire demand is loaded onto the (congested) network. It is assumed that the demand is composed of at least two commodities that exhibit non-identical travel behaviors. The demand changes from one DTA iteration to the next can then be decomposed into two components: (i)demand exchangesbetween commodities, whichdo not affect the total (aggregate over all commodities) demand pattern, and (ii)demand shifts, which do affect the total demandpattern. Given that there are many (day-to-day) sequences of demand and congestion patterns that lead to the same stationaryassignment, the approach taken here is to minimize congestion variability along this path by favoring, to the extent possible,demand exchangesoverdemand shifts. The underlying intuition is that the resulting reduction in congestion variability and consequently better predictability of travel times leads to a faster and/or more stable convergence of the assignment.The selection of replanning rates in general-purpose DTA simulation packages has, due to the limited tractability of suchsystems, received limited attention in the literature. In deterministic settings, flow averaging schemes according to (variantsof) the method of successive averages are often considered (Liu et al., 2007). In stochastic process assignment, constantreplanning rates may be preferred because these can lead to unique stationary process distributions (Watling and Hazelton,2003). The possibly interesting twist of the approach described here is that it (i) leaves the choice of a global replanning rate (being identical for all commodities) to any available algorithm or expert and then (ii) accelerates the convergence of the simulation process by deriving commodity-specific replanning rates. Lu and Mahmassani (2007) and later Lu et al. (2009)pursue the same line of thinking but make more specific modeling assumptions (a route swapping assignment that aims at attaining a deterministic user equilibrium) than what is assumed in the subsequently described method.
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| 38. |
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| 39. |
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| 40. |
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| 41. |
- Flötteröd, Gunnar, et al.
(författare)
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Evacuation simulation with limited capacity sinks
- 2010
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Ingår i: Proceedings of the International Conference on Evolutionary Computation. - Valencia, Spain. - 9789898425317 ; , s. 249-254
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Konferensbidrag (refereegranskat)abstract
- We heuristically solve an evacuation problem with limited capacity shelters. An evolutionary learning al gorithm is developed for the combined route- and shelter-assignment problem. It is complemented with a heuristic method for the fair minimization of shelter capacities. Different behavioral assumptions "fair" vs. "globally optimal") are investigated. The proposed approaches are discussed in the context of a real-world tsunami evacuation problem.
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| 42. |
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| 43. |
- Flötteröd, Gunnar, et al.
(författare)
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Gaming simulations with environmental trajectories that maximize information gain
- 2012
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Ingår i: Proceedings of the 2012 Winter Simulation Conference (WSC). - : IEEE. - 9781467347792 ; , s. 6465068-
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Konferensbidrag (refereegranskat)abstract
- Gaming simulations put real actors in simulated environments. Example applications are training and scenario analysis in transport operations and disaster management. Running a single gaming simulation is an expensive endeavor and therefore must be led through interesting scenario configurations to maximize the learning or research outcomes. This article presents an approach to automatically control the simulated environment in account for the real players' behavior such that a maximum usability of the session is ensured. The approach accesses elements from discrete choice theory and provides the game designer with different options to tailor the type of learning. An archetypical application demonstrates the usefulness of the approach.
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| 44. |
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| 45. |
- Flötteröd, Gunnar, et al.
(författare)
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High-speed combined micro/macro simulation of traffic flow
- 2007
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Ingår i: 2007 IEEE INTELLIGENT TRANSPORTATION SYSTEMS CONFERENCE. - Seattle, USA. ; , s. 926-931
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Konferensbidrag (refereegranskat)abstract
- We describe two new and practically relevant simulation techniques related to the Kinematic Wave Model of traffic flow. Firstly, we demonstrate how the well-known Godunov solution scheme can be run on variable time scales in a computationally very efficient way. Secondly, we demonstrate how the resulting macroscopic traffic flow model can be run in conjunction with a microscopic model of driver behavior while maintaining high computational performance.
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Flötteröd, Gunnar, 1976-, et al.
(författare)
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Intensity and severity of ship conflicts : an AIS based approach
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There is a lack of standardized methods for socio-economic evaluations within the maritime transport sector. This paper presents a model for analysing and quantifying the intensity and severity of ship conflicts using AIS (Automatic Identification System) data and expert assessments. Also, a case study applying the proposed method to the Southern Gothenburg Archipelago is carried out. The goal is to contribute to cost-benefit analyses within the maritime transport sector by a better understanding of how different actions, such as the widening of fairways or new regulation, impact maritime safety. The importance of validating the model by comparing its results with independent sources of reported maritime accidents is emphasized, and the challenges of using existing accident statistics for this purpose is discussed. The basic model described in the paper can be built upon by differentiating parameters by region and vessel type, account for seasonality etc. Furthermore, a downstream consequence analysis model is needed to enable a monetary valuation of (the consequences of) identified conflicts. Finally, the same principles as laid out here for conflict analysis can also be adopted to the identification of groundings.
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| 50. |
- Flötteröd, Gunnar
(författare)
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Macroscopic network loading of microscopic travel demand
- 2009
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Ingår i: New Developments in Transport Planning. - : Edward Elgar Publishers. - 9781848449633 ; , s. 275-291
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Bokkapitel (refereegranskat)abstract
- This chapter describes a computationally efficient technique for the network loading of microscopically represented travel demand with microscopic supply models. Beyond its experimentally demonstrated computational performance, the following features of the demands are worth noting: (i) the microscopic flow model is coupled to the microscopic demand model through a filtering mechanism that effectively removes most vehicle discretization noise; (ii) analytical features such as continuity or differentiability of the macroscopic traffic flow model are preserved despite the microscopic traveler representation.
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