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Report numberRA-2015-004
TitleCrash Patterns at Signalized Intersections
Subtitle
AuthorsEvelien Polders
Stijn Daniels
Elke Hermans
Tom Brijs
Geert Wets
Published byPolicy Research Centre for Traffic Safety 2012-2015
Number of pages33
Date16/04/2015
ISBN
Document language
Partner(s)Universiteit Hasselt
Work packageWP2: Risk analysis
Summary
Background: Intersections are crash prone locations since they are characterized by many conflicting movements, resulting in complexity and large variations in interactions between road users. To minimize the number of conflicts at intersections and to increase traffic safety, intersections are often equipped with traffic signals. Despite the fact that traffic signals separate movements in space and time, severe crashes still occur at these intersections.
 
Objective: In this study, detailed crash information was collected (basic crash data + collision diagrams) about 1295 crashes at 87 signalized intersections. The objective is to draw up a crash profile of signalized intersection crashes and to identify key features of these crashes.
 
Method: The information of the collision diagrams is used to distinguish six different crash types and to create a crash location typology to divide the signalized intersection into 13 detailed and different typical segments. Logistic regression modeling techniques are used to identify relations between crash types, their crash location on certain signalized intersection segments, the crash severity and the different features that affect their crash occurrence.
 
Results: The results indicate that signalized intersections are characterized by four dominant crash types: rear-end, side, vulnerable road user and head-on crashes. Except for rear-end crashes, these crash types are also characterized by higher than expected crash severity levels. The crash location of these dominant crash types is related to specific signalized intersection segments: rear-end crashes occur mostly before the intersection or on the bypass, side and head-on crashes take mostly place on and near the intersection plane while vulnerable road user crashes occur predominantly at the crossing facilities after the intersection plane or on the bypass. Besides the crash location, we also examined the effect of specific signalized intersection properties on the occurrence of the dominant crash types. Protected-only left-turn signal phasing has a positive effect on crashes involving vulnerable road users, head-on and rear-end crashes while protected/permitted left-turn signal phasing increases rear-end crashes. Signalized intersections equipped with red light cameras are characterized by less crashes with vulnerable road users and side and head-on collisions. In addition, red light cameras also result in an increase in rear-end crashes. The presence of a median leads to less head-on collisions while a lower design speed has a favorable impact on the number of injury crashes and crashes involving vulnerable road users.
 
Conclusion: The main goal of this study was to identify and analyze dominant crash types at signalized intersections by taking detailed information on the crash location into account. Some connections between certain signalized intersection crash types, their crash location and signalized intersection design characteristics have been found. The crash location typology method in which a signalized intersection is divided into typical and detailed intersection segments provides valuable insights in the nature of signalized intersection crashes and the safety impact of signalized intersection design.
 
Recommendations: Based on these results, a few recommendations for the design of signalized intersections can be formulated. To address the number of rear-end crashes, it is desirable that the signalized intersections and/or the traffic signals are designed to be sufficiently conspicuous.  Improvements in signal coordination and optimization of  change intervals may also lead to a decrease in rear-end crashes. It is widely acknowledged that side and frontal collisions are above all the result of red-light running or unprotected left-turn phasing. As a result, possible countermeasures include the implementation of protected left-turn phasing and red light cameras even though the latter measure gives rise to increases in rear-end crashes. Additional measures such as improvements in sight  distances, signal coordination  and change intervals may also result in less head-on and side crashes.  A clear road design concept that is easily understandable for road users (e.g. consistent and unambiguous signal phasing for left-turning traffic) leads to a more homogenous road user behavior and is  therefore beneficial. Additionally, motorists in general are more focused on other motorists than on vulnerable road users. Therefore, crossing facilities at signalized intersections should be designed to be clearly visible for approaching drivers. Conflicts between vulnerable road users and motorized vehicles still occur frequently at signalized intersections when they are not fully protected by the signal phasing (i.e. vulnerable road users have the same green phase as turning traffic).  From a safety perspective, protected phasing for vulnerable road users is recommended.
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