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Advancing Traffic Safety: An evaluation of speed limits, vehicle-bicycle interactions, and I2V systems
KTH, School of Architecture and the Built Environment (ABE), Transport Science.ORCID iD: 0000-0002-7080-5176
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Since the introduction of motor vehicles, the number of fatalities and accidents has been a concern for society.The number of fatalities on roads is amongst the most common causes of mortality worldwide (WHO, 2015).Even in industrialized countries the number of fatalities remains unacceptable. Therefore, in the last decades, anumber of approaches have emerged to support and boost traffic safety towards a system free from fatalities andserious impairment outcomes. ‘Sustainable Safety’ and ‘Vision Zero’ are well-known examples aiming to avoidfatalities within the traffic system and reduce injury severity when a traffic accident is inevitable. However, thenumber of fatalities and seriously injured accidents are still relatively high. More specifically, vulnerable roadusers remain involved in fatal and serious accidents even in industrialized countries. Therefore, further advancesin traffic safety studies are needed. This thesis aims at evaluating the impact of road characteristics, traffic rulesand information provision towards a safer traffic system. The thesis is composed of five scientific papers whichsummarizes the main contributions of this work.

Place, publisher, year, edition, pages
Stockholm: KTH , 2016. , 20 p.
Series
TRITA-TSC-PHD, 16-008
Keyword [en]
Traffic safety, urban roads, posted speed limits, road characteristics, free-flow speed, time headway, vehicle-bicycle interactions, logit model, yielding probability, cooperative systems and warning messages.
National Category
Transport Systems and Logistics
Research subject
Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-195640ISBN: 978-91-87353-94-9OAI: oai:DiVA.org:kth-195640DiVA: diva2:1044811
Public defence
2016-12-16, Kollegiesalen, Brinellvägen 8, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20161109

Available from: 2016-11-09 Created: 2016-11-07 Last updated: 2016-11-10Bibliographically approved
List of papers
1. Impact of Speed Limits and Road Characteristics on Free-Flow Speed in Urban Areas
Open this publication in new window or tab >>Impact of Speed Limits and Road Characteristics on Free-Flow Speed in Urban Areas
2016 (English)In: Journal of transportation engineering, ISSN 0733-947X, E-ISSN 1943-5436, Vol. 142, no 2, 04015039Article in journal (Refereed) Published
Abstract [en]

The paper documents studies of posted speed limit (PSL) changes on the free-flow speed on urban roads. Before and after field measurements were conducted, changing the existing PSL from 50 to 40 or 60 km/h. The analysis was conducted on the mean free-flow speed difference and speed variability. The data collected were also used for multiple regression analysis, including PSL changes and selected self-explaining road characteristics. The results showed that a decreased PSL caused a small (1.6 km/h) but significant reduction in the mean free-flow speed and speed variance, which might lead to a 10% reduction of severe injury accidents. Furthermore, the PSL reduction had a larger impact on faster drivers and higher road network classes. Conversely, an increased PSL resulted in a 2.6 km/h increase in the mean free-flow speed but no change on speed variability. The regression results indicated that the free-flow speed was heavily influenced by road characteristics, such as carriageway width, road environments, and the presence of on-street parking and sidewalks. Arterial roads presented the largest impact. The PSL had a relatively small impact.

Keyword
Posted speed limit, Urban roads, Free-flow speed, Road characteristics and traffic safety
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-182774 (URN)10.1061/(ASCE)TE.1943-5436.0000800 (DOI)000368838900001 ()2-s2.0-84955467606 (ScopusID)
Note

QC 20160223

Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2016-11-09Bibliographically approved
2. The free-flow speed estimation: a probabilistic approach Impact of speed limit changes, road characteristics and probability to be constrained
Open this publication in new window or tab >>The free-flow speed estimation: a probabilistic approach Impact of speed limit changes, road characteristics and probability to be constrained
(English)Manuscript (preprint) (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-195659 (URN)
Note

QC 20161107

Available from: 2016-11-07 Created: 2016-11-07 Last updated: 2016-11-09Bibliographically approved
3. When do drivers yield to cyclists at unsignalized roundabouts?: Empirical evidence and behavioral analysis
Open this publication in new window or tab >>When do drivers yield to cyclists at unsignalized roundabouts?: Empirical evidence and behavioral analysis
2015 (English)In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2520, 25-31 p.Article in journal (Refereed) Published
Abstract [en]

Cycling popularity has shown an increasing trend during the last decades in many cities of Europe and USA because of its environmental and health benefits. However, cyclists are frequently involved in traffic accidents, especially, when they interact with vehicles at unsignalized intersections. There is still lack of evidence and analysis on how such interaction is performed. This paper explores empirical evidence of the vehicle-bicycle interaction on a typical Swedish roundabout, and provides insights into factors influencing car drivers’ yielding decisions when they interact with cyclists. The vehicle-bicycle interaction was divided into category groups (Non-Conflict, Conflict, Yield, and Non-Yield) and their speed differences were analyzed by group. Furthermore, a discrete choice model was developed to estimate behavioral aspects of such interactions. The observed data showed a higher and significant speed variation among vehicles, whereas bicycles exhibited lower variation across the groups. The modelling results revealed that the yielding probability decreased when the speed of the vehicle was higher. On the other hand, the bicycle speed had little impact on drivers’ decision to yield. More importantly, the yielding probability increased significantly by the proximity of the cyclist to the conflicting zone. The yielding rate of drivers can be improved by keeping vehicles’ speed under 20 km/h, as drivers have the capacity to detect and yield to cyclists.  

Keyword
Vehicle-bicycle interaction, roundabout, yielding behavior, logistic regression models
National Category
Transport Systems and Logistics
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-163553 (URN)10.3141/2520-04 (DOI)000371445000004 ()
Conference
94th Annual Meeting of The Transportation Research Board. January 11-15, 2015 Washington, D.C., USA
Projects
CycleSafe
Note

QC 20150417. QC 20160411

Available from: 2015-04-08 Created: 2015-04-08 Last updated: 2016-11-09Bibliographically approved
4. Analysis of vehicle-bicycle interactions at unsignalized crossings: A probabilistic approach and application
Open this publication in new window or tab >>Analysis of vehicle-bicycle interactions at unsignalized crossings: A probabilistic approach and application
2016 (English)In: Accident Analysis and Prevention, ISSN 0001-4575, E-ISSN 1879-2057, Vol. 97, 38-48 p.Article in journal (Refereed) Published
Abstract [en]

In the last decades, bicycle usage has been increasing in many countries due to the potential environmental and health benefits. Therefore, there is a need to better understand cyclists’ interactions with vehicles, and to build models and tools for evaluating multimodal transportation infrastructure with respect to cycling safety, accessibility, and other planning aspects. This paper presents a modeling framework to describe driver-cyclist interactions when they are approaching a conflicting zone. In particular, the car driver yielding behavior is modeled as a function of a number of explanatory variables. A two-level hierarchical, probabilistic framework (based on discrete choice theory) is proposed to capture the driver’s yielding decision process when interacting with a cyclist. The first level models the probability of the car driver perceiving a situation with a bicycle as a potential conflict whereas the second models the probability of yielding given that a conflict has been perceived by the driver. The framework also incorporates the randomness of the location of the drivers’ decision point. The methodology is applied in a case study using observations at a typical Swedish roundabout. The results show that the conflict probability is affected differently depending on the user (cyclist or driver) who arrives at the interaction zone first. The yielding probability depends on the speed of the vehicle and the proximity of the cyclist.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Vehicle-bicycle interaction, Cyclist safety, Yielding behavior, Unsignalized intersection, Roundabout, Logit model, Maximum likelihood estimation
National Category
Transport Systems and Logistics
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-192586 (URN)
Note

QC 20160923

Available from: 2016-09-15 Created: 2016-09-15 Last updated: 2016-11-09Bibliographically approved
5. Simulation-based evaluation of I2V systems' impact on traffic performance: Case study - COOPERS
Open this publication in new window or tab >>Simulation-based evaluation of I2V systems' impact on traffic performance: Case study - COOPERS
2014 (English)In: WIT Transactions on the Built Environment, 2014, 429-446 p.Conference paper (Refereed)
Abstract [en]

In-vehicle technologies and cooperative services are attracting a lot of attention for their potential to deal with congestion problems and improve traffic safety. This paper aims to investigate the impact of infrastructure-to-vehicle cooperative systems, case of COOPERS, at the aggregate level, on traffic performance. A factorial experiment is designed with two factors: traffic demand and penetration of the system with three levels each. In total, nine scenarios are investigated. To replicate driving behavior with and without the system, speed distributions from a simulator experiment are used. A motorway section of 4 km is built in VISSIM simulation software. Indicators such as speed, density, delays and travel times are chosen to evaluate and compare the motorway performance with and without the system. The results show that drivers driving with the system activated are more aware and alert to near future traffic conditions compared to driving without the system. Driving with the system activated is characterized by smoother and longer speed decelerations when approaching critical incident/accident events. The results show as well that the factors investigated significantly impact the motorway performance. Congestion reduces the impact of the system whereas higher penetration levels improve traffic operation on the motorway. Future research directions can include (1) investigating the impact of the system at the micro level such as lane changing or car-following behaviors; (2) levels of compliance with the system, which is an important aspect as well.

Keyword
Cooperative systems, Driver simulator, Driving behavior, Factorial experiment, Micro simulation, Traffic performance, Behavioral research, Computer software, Experiments, Urban transportation, Co-operative systems, Microsimulation, Traffic congestion, cooperative behavior, demand analysis, numerical model, performance assessment, technological development, traffic management, transportation infrastructure, transportation safety
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-167908 (URN)10.2495/UT140361 (DOI)2-s2.0-84903136075 (ScopusID)9781845647780 (ISBN)
Conference
20th International Conference on Urban Transport and the Environment, UT 2014, 28 May 2014 through 30 May 2014, Algarve
Note

QC 20150608

Available from: 2015-06-08 Created: 2015-05-22 Last updated: 2016-11-09Bibliographically approved

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