| 1. |
- Al-Mudhaffar, Azhar, 1957-
(författare)
-
Impacts of Traffic Signal Control Strategies
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traffic signals are very cost effective tools for urban traffic management in urban areas. The number of intersections in Sweden controlled by traffic signals has increased since the seventies, but efforts to study the traffic performance of the employed strategies are still lacking. The LHOVRA technique is the predominant isolated traffic signal control strategy in Sweden. Past-end green was originally incorporated as part of LHOVRA (the “O” function) and was intended to reduce the number of vehicles in the dilemma zone. Coordinated signal control in Sweden is often fixed-time with local vehicle actuated signal timing adjustments and bus priority. This research study was undertaken to increase the knowledge of the traffic performance impacts of these strategies. The aim was to evaluate the following control strategies using Stockholm as a case study: 1. The LHOVRA technique with a focus on the “O” function; 2. Fixed time coordination (FTC); 3. Fixed time coordination with local signal timing adjustment (FTC-LTA); 4. FTC-LTA as above + active bus priority (PRIBUSS); 5. Self-optimizing control (SPOT). Field measurements were used for study of driver behavior and traffic impacts as well as for collecting input data needs for simulation. The results from low speed approaches showed a higher proportion of stopped vehicles after receiving green extension. Moving the detectors closer to the stop line, and/or making the detectors speed dependent were suggested as measures to solve these problems. The VISSIM simulation model calibrated and validated with empirical data was used to study traffic performance and safety impacts of the LHOVRA technique as well as to test the suggested improvements. The simulation experiment results from these design changes were shown to reduce accident risk with little or no loss of traffic performance. TRANSYT was used to produce optimized fixed signal timings for coordinated intersections. HUTSIM simulations showed that local signal timing adjustment by means of past-end green was beneficial when applied to coordinated traffic signal control in the study area. Both delays and stops were reduced, although not for the main, critical intersection which operated close to capacity. To study the impacts of strategies for coordinated signal control with bus priority, extensive field data collection was undertaken during separate time periods with these strategies in the same area using mobile and stationary techniques. A method to calculate the approach delay was developed based on the observed number of queuing vehicles at the start and end of green. Compared to FTC-LTA, the study showed that PRIBUSS reduced bus travel time. SPOT reduced both bus and vehicle travel time. Future research efforts for the development of signal control strategies and their implementation in Sweden should be focused on strategies with self-optimization functionality.
|
|
| 2. |
- Andersson, Johan Vium, 1971-
(författare)
-
A Complete Model for Displacement Monitoring Based on Undifferenced GPS Observations
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During recent years there has been a great focus on the climate changes within the media. More or less every day more newspaper articles are presented about the global warming issue and the effect on us human race. Climate models predict higher temperatures and more rain in the northern part of Europe. It is also predicted that the weather will become more extreme e.g. it will rain a lot during longer periods than has been the norm. If these predictions are correct, the amount of water that is going to be transported away in streams and rivers will increase and so also will the subsoil water level. The latter increases the risk for landslides in areas with fine grained soils. An early warning system that is able to alert people before a landslide take place would be of great interest. The purpose of this work is to develop a complete real-time displacement monitoring system based on observations from several GPS-receivers that could be used as an early warning system. Due to the complex correlation structure of the traditionally used double differences, an alternative method based on undifferenced observations is used. Theoretically this approach shows some advantages and simplifies the correlative structure of observables compared to the double differenced method. A complete model for the undifferenced approach is presented in this thesis including its software implementation. A displacement detection system includes not only the positioning algorithms, but also methods to detect if any displacement occurs. There are many methods available to discriminate displacements, which are used in the traditional control of manufacturing processes. Several of these methods are compared in this thesis, such as the Shewhart chart, different Weighted Moving Average (WMA) charts and the CUmulative SUMmation (CUSUM). Practical tests show that it is possible to detect an abrupt shift on sub centimetre level at the same epoch as the shift occurs. Smaller shifts are also detectable with the applied approach but with a slightly longer detection time.
|
|
| 3. |
- Andersson, Mats, 1965-
(författare)
-
Empirical Essays on Railway Infrastructure Costs in Sweden
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis concerns pricing the use of transport infrastructure. We are empirically investigating the relationship between railway traffic volumes and infrastructure management costs. More specifically, we are interested in estimating the change in infrastructure management costs from marginal variations in traffic volumes, i.e. to estimate the marginal cost of railway infrastructure wear and tear. Both Europe and Sweden have moved towards a marginal cost based transport pricing policy, thus driving the need for more empirical work on rail infrastructure costs to underpin the level of a wear and tear charge. The thesis consists of five papers. In paper I, the data situation for planning railway maintenance and renewal is surveyed internationally. The survey indicates that most infrastructure managers are still in the data gathering phase, rather than ready to use modern computerised planning tools to make sound decisions in the field of maintenance and renewal. In paper II, we investigate the data situation for infrastructure cost analysis in Sweden. A panel data set that consists of cost, traffic and infrastructure information is created. The data covers 1999-2002 and contains almost 190 annual observations. Three main cost categories are identified; infrastructure operation, maintenance and renewal. This data is used for estimations of cost functions in paper II, III and V. Econometric techniques are applied for this purpose, with several different model specifications. In paper II, the method of pooled ordinary least squares (POLS) is applied. In paper III, we turn to unobserved effects models to exploit data heterogeneity. Finally in paper V, a dynamic generalised method of moments estimator is used to explore a potential dynamic cost dependency. The main findings are that the POLS approach, which has been used in similar studies in Europe recently, is rejected in favour of fixed effects estimation for this data. Furthermore, we also reject the idea of regression analysis to capture marginal rail renewal costs. In paper IV, we suggest an analytical expression combined with survival analysis of rail ages to estimate marginal renewal costs. We derive elasticities with respect to output as well as marginal costs for the different cost categories, and find that the current charge for wear and tear in Sweden is well below these new estimates. This opens up for increased, marginal cost based rail infrastructure wear and tear charges, which would reduce the financial burden on Swedish tax-payers.
|
|
| 4. |
- Aronsson, Karin F. M.
(författare)
-
Speed characteristics of urban streets based on driver behaviour studies and simulation
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of the study was to gain in-depth knowledge of speed relationships for urban streets. The speed characteristics were examined using a number of methods for data collection. Throughout the research, a special focus was placed on capturing the influence on driver speed of interactions with pedestrians, cyclists and other road users, called sidefriction events in this study. First, driver behaviour and travel time data was collected from field and driving simulator studies for a range of street types and traffic conditions. The collected data was used to calibrate a microscopic traffic simulation model. Production runs with this model were performed for various traffic conditions. Second, aggregated speed data was collected at the link level, i.e. the macro level, for three street types. In combination with street site variables, speed and flow data was analysed using multiple regression techniques with space mean speed as dependent variable. This analysis was also performed for average travel speed data produced by microscopic traffic simulation. Two central results were attained and utilized for the model development: - In-depth knowledge of which factors influence speed choice on urban street links with minor intersections, on a micro and macro level. - A comprehensive research methodology for study of speed characteristics on urban streets in which the knowledge gained at the micro and macro level was applied. Results from the micro study showed that Average number of crossing pedestrians and Traffic flow had significant impact on average travel speed (R2=0.91). Results from the macro study performed for three street types showed that Street function and Number of lanes also had a high degree of explanation (R2 close to 0.70). The variables Separated bicycle lane, Roadside parking permitted and Number of minor intersections per 1 km were significant for some of the street types modelled in the macro study. The variables Ratio of through vehicles and Gender of the driver were also investigated and were found not to influence space-mean speed. The macro study demonstrated that speed choice and driver behaviour were consistent for each street type investigated regardless of city type and population size. The speed-flow relationships of the micro model for an urban street type showed good agreement with the macro model for traffic flows in the upper range. In conclusion, the research effort showed that the included side-friction variables added explanatory value to the estimation of speed, and thus can enhance the knowledge of traffic impacts of different urban street designs.
|
|
| 5. |
- Baltzopoulos, Apostolos, 1981-
(författare)
-
Essays on High-Quality Entrepreneurship : On the Origins and Survival of Start-ups and the Role of Universities in the Location Decision
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of four self-contained essays on the topic of entrepreneurship. [Essay I] uses a unique and detailed Swedish dataset to explore firm, regional, and industry determinants that stimulate spin-offs using the choice of the individuals as the level of analysis. The most important results are that the size of the region and of the local entrepreneurial culture (the relative number of SMEs) has a positive effect on the propensity of the individual to set up a new venture corroborating the results of past firm- and regional-level studies. Industrial specialization is shown to have a positive impact on spin-offs, albeit only in high-tech manufacturing and in knowledge intensive business service sectors. Moreover, using an entropy measure to disentangle unrelated and related variety, it is found that the former has a significantly negative while the latter a significantly positive effect on the propensity of the individual to start a spin-off. [Essay II] asks how localisation (MAR) and diversity (Jacobs) externalities affect opportunity-based entrepreneurship across all industry sectors in Sweden’s private economy in the period 1999-2005. MAR externalities are found to positively affect entrepreneurship across all sectors. Jacobs externalities, measured as related variety using an entropy measure, positively affect entrepreneurship in high-tech manufacturing and in knowledge intensive business services but have no significant effect on low-tech manufacturing and other services. The results suggest that previous studies that find no evidence of entrepreneurship benefiting from a diverse local market composition might be using too broad measures of variety. [Essay III] analyses how different R&D strategies of incumbent firms affect the quantity and quality of their entrepreneurial spawning. By examining entrepreneurial ventures of ex-employees of firms with different R&D strategies three things emerge: First, firms with persistent R&D investments with a general superiority in sales, exports, productivity, profitability and wages are less likely to generate entrepreneurs than firm with temporary or no R&D investments. Second, start-ups from knowledge intensive business service (KIBS) firms with persistent R&D investments have a significantly increased probability of survival. No corresponding association between the R&D strategies of incumbents and survival of entrepreneurial spawns is found for incumbents in manufacturing sectors. Third, spin-outs from KIBS-firms are more likely to survive if they start in the same firm, indicating the importance of inherited related knowledge. The findings suggest that R&D intensive firms spur fewer entrepreneurs, but their entrepreneurial spawns tend to be of higher quality. [Essay IV] investigates how universities may affect regional entrepreneurship through the localisation decisions of entrepreneurial alumni. Empirically, a comprehensive, individual-level dataset from Sweden is used for the period 2003-2005. The results suggest that even when controlling for their spatial history, individuals have an increased propensity to set up in the region where they studied. This effect is found to substitute for both urbanisation economies and localisation economies as drivers of regional-level entrepreneurship. Thus, the analysis provides evidence on how universities affect regional economic development that complements the strong focus on spin-off activities by university researchers in previous studies.
|
|
| 6. |
- Broström, Anders, 1978-
(författare)
-
Strategists and Academics :
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis consists of five self-contained essays on interaction in R&D between university researchers and private firms. Together, these essays explore the conditions under which private firms benefit from spillovers from publicly funded and organised research. From the first essay, which sets out to empirically validate the theoretical arguments about the benefits of university-industry interaction for private firms, the thesis follows a line of pursuit that goes back and forth between exploration of the different benefits that firms enjoy from university interaction and the relationships between these benefits and the conditions of interaction. In essay II, a typology of rationales for establishing cooperative relations is presented. A considerable breadth of interaction rationales is documented, but on closer examination, a “core” set of rationales related to innovation in terms of invented or improved products or processes are found to be the main drivers of interaction. Developing this view, three critical issues previously studied within innovation economics are re-considered from the point of view of firm rationales for interaction; public co-funding of university-firm interaction (essay II), the role of geographic proximity for interaction on R&D (essay III) and the organisation of public sector research (public research institutes and universities) in relation to firm level competences (essay IV). In a fifth essay, four ideal types of strategy for localised interaction between R&D subsidiaries and universities are proposed. Through the framework developed in this essay, the rationales for interaction are related to the overall R&D strategy of multinational firms. Concluding the thesis, it is discussed how the research presented herein opens up for improved theorizing around the roles of academic research for industrial innovation.
|
|
| 7. |
- Börjesson, Maria, 1974-
(författare)
-
Issues in Urban Travel Demand Modelling : ICT Implications and Trip timing choice
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Travel demand forecasting is essential for many decisions, such as infrastructure investments and policy measures. Traditionally travel demand modelling has considered trip frequency, mode, destination and route choice. This thesis considers two other choice dimensions, hypothesised to have implications for travel demand forecasting. The first part investigates how the increased possibilities to overcome space that ICT (information and communication technology) provides, can be integrated in travel demand forecasting models. We find that possibilities of modelling substitution effects are limited, irrespective of data source and modelling approach. Telecommuting explains, however, a very small part of variation in work trip frequency. It is therefore not urgent to include effects from telecommuting in travel demand forecasting. The results indicate that telecommuting is a privilege for certain groups of employees, and we therefore expect that negative attitudes from management, job suitability and lack of equipment are important obstacles. We find also that company benefits can be obtained from telecommuting. No evidences that telecommuting gives rise to urban sprawl is, however, found. Hence, there is ground for promoting telecommuting from a societal, individual and company perspective.The second part develops a departure time choice model in a mixed logit framework. This model explains how travellers trade-off travel time, travel time variability, monetary and scheduling costs, when choosing departure time. We explicitly account for correlation in unobserved heterogeneity over repeated SP choices, which was fundamental for accurate estimation of the substitution pattern. Temporal constraints at destination are found to mainly restrict late arrival. Constraints at origin mainly restrict early departure. Sensitivity to travel time uncertainty depends on trip type and intended arrival time. Given appropriate input data and a calibrated dynamic assignment model, the model can be applied to forecast peak-spreading effects in congested networks. Combined stated preference (SP) and revealed preference (RP) data is used, which has provided an opportunity to compare observed and stated behaviour. Such analysis has previously not been carried out and indicates that there are systematic differences in RP and SP data.
|
|
| 8. |
- Chiguma, Masatu L. M., 1955-
(författare)
-
Analysis of side friction impacts on urban roads : Case study Dar-es-Salaam
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Side friction factors are defined as all those actions related to the activities taking place by the sides of the road and sometimes within the road, which interfere with the traffic flow on the travelled way. They include but not limited to pedestrians, bicycles, non-motorised vehicles, parked and stopping vehicles. These factors are normally very frequent in densely populated areas in developing countries, while they are random and sparse in developed countries making it of less interest for research and consequently there is comparatively little literature about them. The objective of this thesis is to analyze the effect of these factors on traffic performance measures on urban roads.To carry out this work, a research design was formulated including specific methods and prescribed limitations. An empirical case study methodology was adopted where Dar-es-salaam city in Tanzania was chosen as a representative case. The scope was limited to include only road-link facilities. A sample of these facilities including two-lane two-way and four-lane two-way roads were selected and studied. The study was conducted in two parts, of which each involved a distinctive approach. Part one involved a macroscopic approach where traffic and friction data were collected and analyzed at an aggregated level, whereas part two involved a microscopic approach where data of individual frictional elements were collected and analysed individually. Data collection was mainly performed by application of video method, which proved to be effective for simultaneous collection of traffic and side friction data. Data reduction was conducted chiefly by computer, using standard spreadsheet and statistical software packages, mainly SPSS and some computer macros.The analysis part was based on statistical methods, chiefly regression analysis. In the macroscopic approach, traffic and friction data from all sites were adjusted through a process called ‘normalization’, which enabled the data from the different sites to be merged, and consequently to obtain speed-flow curves for each road type. The individual friction factors through regression analysis were weighted and combined into one unit of measure of friction called "FRIC". The effect of "FRIC" on speed-flow curves was analyzed. The results showed significant impact on speed for both road types. Impact on capacity was identified on two-lane two-way roads while field data on four-lane two-way roads did not allow this. In the microanalysis approach, effect of individual side friction factors on speed was analyzed. The results showed that on two-lane two-way roads, all studied factors exhibited statistically significant impact on speed, while on four-lane two-way roads, only one factor showed the same. The results also identified impact values characteristic to the individual friction factors on some roads.Recommendations were made based on these results that highway capacity studies particularly in developing countries, should include the friction variable, though in the form suitable to their own particular circumstances. Further recommendations were made that these results should be applied to formulate management programs seeking to limit levels of side friction on high mobility urban arterial streets in order to improve traffic safety and operation efficiency.
|
|
| 9. |
- Dziekan, Katrin, 1976-
(författare)
-
Ease-of-Use in Public Transportation : A User Perspective on Information and Orientation Aspects
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This interdisciplinary thesis combines psychological and transportation planning knowledge. Three main questions are investigated: 1) What concepts and ideas do people have with regard to a public transportation system (cognitive user perspective)?; 2) What orientation and information factors within the public transportation system enhance Ease-of-Use and make it simpler and more efficient to use public transportation in metropolitan areas?; 3) How can Ease-of-Use of a public transportation route be measured? A combination of qualitative and quantitative methods was used. Between 2002 and 2007 a total of nine different studies were conducted: An in-depth study on a single exchange student, an interview study with exchange students, a questionnaire study on exchange students, a before-after interview study with travellers on selected bus stops, an before-after telephone interview study on residents, an expert questionnaire study via email, a behaviour observation study on travellers, a before-after questionnaire study on travellers on a tram line, and an on-board questionnaire study. To analyse the cognitive user perspective the term memory representation was introduced, that includes cognitive maps of and additional knowledge about a public transportation system such as service frequency. Memory representation is influenced by experience. Three learning phases in an unknown public transportation system are proposed and a general information search script is described. A new approach is presented regarding the organisation of public transportation knowledge: The ground level is that there exists a public transportation option, the next level is the identification of the mode of transport and at the highest level of the hierarchy is the code for the line. Within the second level, the public transportation mode, a hierarchical structure of public transportation option knowledge is proposed. Three factors are postulated that contribute to the extent to which a line is represented in people’s memory: visibility, straight route layout and labelling. Which orientation and information factors within the public transportation system enhance Ease-of-Use, i.e. match the cognitive user perspective? It was found that trunk bus lines enhanced Ease-of-Use and at-stop real-time information can have various positive effects. The role of good maps is explained and stretched and the importance of consistent information throughout the travel chain is also pointed out. In addition, many valuable concrete hints are given with regard to how to match the system properly with the cognitive user perspective. Undoubtedly, an interaction exists between system and user and they influence each other. This is where the third research question comes in: How can Ease-of-Use in public transportation systems be measured? The iterative process of defining and measuring Ease-of-Use resulted in a scale that measured the defined concept well with good reliability and validity. The final discussion highlights the contribution to science of this thesis and presents some possible paths for further research. The thesis consists of a summary and eight papers.
|
|
| 10. |
|
|
