Among the most critical elements at signalized intersections are the design of vehicle detection equipment and the timing of change and clearance intervals. Improperly timed clearance intervals or improperly placed detection equipment can potentially place drivers in a Type I dilemma zone, where approaching motorists can neither proceed through the intersection before opposing traffic is released nor safely stop in advance of the stop bar. Type II dilemma zones are not necessarily tied to failures in design, but are more readily tied to difficulties in driver decision making associated with comprehension and behavior. The Type II dilemma zone issues become even more prevalent at high-speed intersections where there is greater potential for serious crashes and more variability in vehicle operating speeds. This research initiative attempts to further describe the impact of driver behavior and comprehension on dilemma zones. To address this notion several experiments are proposed. First, a large empirical observation of high-speed signalized intersections is undertaken at 10 intersection approaches in Vermont. This resulted in the collection of video and speed data as well as full intersection inventories and signal timings. These observations are reduced and analyzed for the purpose of reexamining the boundaries of a Type II dilemma zone. Second, a comparison of point and space sensors for the purpose of dilemma zone mitigation was conducted. This experiment provides evidence supporting the notion that space sensors have the potential for providing superior dilemma zone protection. Third, a computer based survey is conducted to identify if drivers comprehend the correct meaning of the solid yellow indication and how this relates to their predicted behavior. Lastly, a regression model is developed drawing on the data collected from the field observation as well as the static survey to determine how characteristics such as the speed and position of the vehicle as well as driver age and experience influence driver behavior in the Type II dilemma zone. Cumulatively, these experiments will shed additional light on the influence of driver behavior and comprehension on the Type II dilemma zone.

Children are, by law, required to use specialised child restraint systems (CRS) when riding in cars. The protective capabilities are required as the children’s bodies are not developed enough toproperly take the forces of a collision (Folksam, 2019). CRS today are regulated by various standards and have proven to be very efficient in protecting the child, but incorrect use reduces the effectiveness of the restraints. This thesis was carried out in collaboration with Folksam to study the frequency of misuse within Stockholm, Sweden and to design a CRS that combats them. The study involved a larger observation study that took place in 12 different and randomly selected kindergartens around the greater Stockholm area. The findings showed that CRS fastened with ISOFIX had double the rate (82%) of correct installation in comparison to belt fastening (42%). At the same time, belt fastening was also much more common (72% occurrence rate) than ISOFIX. 10.9% of all registered did not use a CRS at all. The most common misuse was found to be for group 1 CRS, generally being around too loose tether straps and incorrect use of internal belt. The conceptual designs were developed using both quantitative and qualitative research methods and were then evaluated on how well they fulfilled each requirement. A double belt concept was chosen due to its potential to minimise misuse the most. The thesis ended with concluding that its purpose has been fulfilled and includes recommendations for future work. / Barn behöver, enligt lag, använda specialiserad skyddsutrustning (bilbarnstol) när de färdas i bil. De skyddande egenskaperna är nödvändigt för barnen då deras kroppar inte har utvecklats tillräckligt än för att hantera kollisioner (Folksam, 2019). Idag är bilbarnstolar reglerade av olika standarder som har visats kunna skydda barnen, men felanvändning gör att effektiviteten sänks. Denna uppsats är gjord i samarbete med Folksam för att studera bilbarnstolars felanvändning samt ett designkoncept av en bilbarnstol för att motarbeta dem. Studien innefattade en större observationsstudie som tog plats på 12 olika, slumpmässigt utvalda förskolor i Stockholmsområdet. Studien visade att bilbarnstolar med ISOFIX fäste har en högre andel korrektanvändning (84%) än bältesinfästning (42%) inom grupp 1 bilbarnstolar. Det identifierades också att endast 27% av alla bilbarnstolar inom grupp 1 klassificeringen hade ISOFIX. 10,9% av alla som deltog i undersökningen använde sig inte av någon typ av bilbarnstol. De vanligaste felanvändningarna var för grupp 1 bilbarnstolar, där underförankringsband oftast var för löst samt inkorrekt användning av internbälte. Koncept på den föreslagna bilbarnstolen skapades med hjälp av både kvantitativa och kvalitativa forskningsmetoder, där koncepten sedan evaluerades beroende på hur bra dem uppfyller olika krav. Ett dubbel-bälteskoncept blev valt för att det visade störst potential att minska felanvändning. Denna uppsats avslutades med att målet blev uppfyllt samt att rekommendationer gavs för fortsatt arbete.

Data-driven intelligent transportation systems (ITS) are increasingly playing a critical role in improving the efficiency of the existing transportation network and addressing traffic challenges in large cities, such as safety and road congestion. This dissertation employs data dimensionality reduction, reinforcement learning, and discrete outcome models to improve traffic flow and transportation safety. First, we propose a novel data-driven technique based on Koopman operator theory and dynamic mode decomposition (DMD) to address the complex nonlinear dynamics of signalized intersections. This approach not only provides a better understanding of intersection behavior but also offers faster computation times, making it a valuable tool for system identification and controller design. It represents a significant step towards more efficient and effective traffic management solutions. Second, we propose an innovative phase-switching approach for traffic light control using deep reinforcement learning, enhancing the efficiency of signalized intersections. The novel reward function, based on speed, waiting time, deceleration, and time to collision (TTC) for each vehicle, maximizes traffic flow and safety through real-time optimization. Finally, we introduce a mixed spline indicator pooled model, an approach for multivariate crash severity prediction, addressing the limitations of previous models by capturing temporal instability. It carefully incorporates additional independent variables to measure parameter slope changes over time, enhancing data fit and predictive accuracy. The developed models are estimated and validated using data from the Central Florida region.

This thesis focuses on evaluating the appropriate speed at which vehicles should travel under different traffic conditions on freeways and its impact on crash frequency. The common belief is that the lower speed results in fewer crashes as reduced speed provides drivers with more time to react effectively and avoid collisions. However, this perspective overlooks the interplay among traffic speed, average spacing between consecutive vehicles, and the distance available for stopping a vehicle. Hence, we propose a safety parameter termed ‘Safety Correlate' (SCORE), which is defined as the proportion of average spacing relative to the stopping distance. To determine the relationship between SCORE and crash frequency, data from 366 4-lane urban freeway segments located in Virginia was analyzed and a Random-effects Poisson Lognormal model was developed. The obtained result indicated that the safety parameter SCORE is negatively associated with the annual hourly crash frequency, implying that the lesser the average spacing as a proportion of the stopping distance while traffic flow remains constant, the more frequent will be the crashes. Additionally, this research presents an application of SCORE in setting variable speed limits under various traffic flows. Overall, the study results provide valuable insights by investigating SCORE to improve traffic safety. Also, this research would help practitioners and policymakers to incorporate safety aspects while setting variable speed limits on freeways.

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Den här uppsatsen handlar om cyklisters trygghet och säkerhet. Malmö är en bra cykelstad med många fina cykelstråk och Malmö stad satsar mycket på att få fler invånare att börja cykla. Det är dock viktigt att planera staden så den känns trygg och säker att cykla i. Syftet med vår undersökning blev därför att ta reda på om de som cyklar i Malmö idag känner sig trygga och på vilket sätt tryggheten påverkas av olika faktorer som planerare arbetar med. Vi har gjort snabbintervjuer med cyklister som cyklar dagligen och efter det gjorde vi djupare intervjuer med två av dessa cyklister. Vi har även intervjuat två planerare som arbetar på gatukontoret i Malmö, samt dokumenterat olika platser som upplevs osäkra att cykla på.För att analysera vårt empiriska material har begreppen plats, mobilitet och trafikseparering använts. Definitioner av risk och riskbedömning används också för att förstå hur cyklisters upplevda trygghet påverkas av olika trafiksituationer. Uppsatsen behandlar dessutom hur cykelplanering i Malmö prioriteras och de åtgärder som finns för att öka cyklisternas framkomlighet och säkerhet i staden. / This thesis is about cyclists and their safety in the city. Malmö is a very good city for cyclists with a lot of different bicycle paths and the municipality (Malmö stad) makes a lot of efforts to make more people choose the bicycle as a transport. It is important to plan the city to make it safe and secure for cyclists. The purpose of our essay is therefore to see if the cyclists of Malmö feel safe and in what way the safety is affected by different elements that the planners work with. We have made quick interviews with everyday cycists and with two of them we made deeper interviews. We have also interviewed two planners from the roadworks department in Malmö and documented different places that feels unsafe for the interviewees to use.To analyze our empirical material we use the the concepts place, mobility and traffic separation. We also define risk and risk assessment to better understand how cyclists perceive their safety in different situations in traffic. The essay also discuss how the planning for cyclists are prioritized in Malmö and the existing arrangements for the cyclists passability and safety in the city.

Dilemma zone (DZ), also called decision zone in other literature, is an area where drivers face an indecisiveness of stopping or crossing at the yellow onset. The DZ issue is a major reason for the crashes at high-speed signalized intersections. As a result, how to prevent approaching vehicles from being caught in the DZ is a widely concerning issue. In this dissertation, the author addressed several DZ-associated issues, including the new stochastic safety measure, namely dilemma hazard, that indicates the vehicles' changing unsafe levels when they are approaching intersections, the optimal advance detector configurations for the multi-detector green extension systems, the new dilemma zone protection algorithm based on the Markov process, and the simulation-based optimization of traffic signal systems with the retrospective approximation concept. The findings include: the dilemma hazard reaches the maximum when a vehicle moves in the dilemma zone and it can be calculated according the caught vehicles' time to the intersection; the new (optimized) GES design can significantly improve the safety, but slightly improve the efficiency; the Markov process can be used in the dilemma zone protection, and the Markov-process-based dilemma zone protection system can outperform the prevailing dilemma zone protection system, the detection-control system (D-CS). When the data collection has higher fidelity, the new system will have an even better performance. The retrospective approximation technique can identify the sufficient, but not excessive, simulation efforts to model the true system and the new optimization algorithm can converge fast, as well as accommodate the requirements by the RA technique. / Ph. D.