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Effectiveness of Bicycle Signals for Improving Safety and Miltimodal Mobility at Urban Intersections

PIs: Jun-Seok Oh, Valerian Kwigizile

Project Start and End Dates: September 1, 2016 – August 31, 2018

 

Summary:

With the dramatic increase of non-motorized transportation users, more people are concerned about the non-motorized traffic safety. Unfortunately, bicyclists and pedestrians are prone to more severe injuries when involved in a crash. For bicycle crashes, failing to yield/disregarding traffic control device, and lack of non-motorized facilities were identified to be the main causes of bicycle crashes in urban intersections. This research investigated the effectiveness of two bicycle crash countermeasures with bicycle signal treatments at urban signalized intersections. These two countermeasures are the bike boxes and the protected intersections. The bicycle signal treatments that were tested simultaneously with these countermeasures are the leading bicycle interval and the exclusive bicycle phase. A before and after bicyclist survey was conducted to measure bicyclist perception of safety of the bike box and bicycle signal heads. Additionally, these engineering countermeasures were evaluated from both traffic operation and traffic safety prospective in a virtual test environment built in VISSIM. Users delay were compared before and after implementing these countermeasures. While a surrogate safety measure “conflicts” among users was used to measure the safety impact of such treatments. Through performing benefit-cost analysis, the threshold values of traffic and bike volumes that are needed to justify the bike box and the protected intersection treatments were found. This research also provided a general guideline that can be used by the decision makers to facilitate bicyclist left turn movement at urban signalized intersections.

Problem:

Walking and biking are considered to be the main non-motorized modes for many people these days, especially in urbanized areas. With the dramatic increase of the non-motorized transportation users, more people are concerned about the non-motorized traffic safety, as it can be a limiting factor of engaging new cyclists. In Michigan, walking, running, and biking continue to grow every year in popularity. Unfortunately, bicyclist and pedestrians are prone to more severe injuries when involved in a crash, and the number of non-motorized crashes have been increasing in recent years. Statistics of non-motorized crash data showed that the majority of pedestrian and bicycle crashes occur at or near intersections and on urban streets. For bicycle crashes, failing to yield/disregarding traffic control was identified as one of the main causes of bicycle crashes in Michigan. Analysis indicated that lack of facilities that accommodate bicyclist (dedicated or shared) may encourage bicyclist to ride on sidewalks. Most of “failing to yield/disregarding traffic control” bicycle crashes involved a bicyclist who was riding on a sidewalk prior to the crash. Countermeasures for bicycle crashes in Michigan were limited to conventional ones while many cities began introducing advanced bicycle infrastructure, such as bike boxes, protected intersections, and bicycle signal treatments. Therefore, it is believed that introducing such new countermeasures may have a positive impact on engaging more bicyclist and promoting more livable and sustainable communities. The main objective of this research is to investigate the effectiveness of two bicycle crashes countermeasures with bicycle signal treatments at urban signalized intersection. These two countermeasures are: the bike box and protected intersection.

Research Results:

A bicyclist survey was conducted to measure bicyclists’ perception on safety of bike box and bike signal, and to assess bicyclists’ knowledge, understanding, and other reactions to the new treatments. The bicyclist survey revealed that presence of bike box would positively impact on bicyclists’ perception on safety and promote bicycle use.

In this study, a simulation approach using a microscopic simulation tool VISSIM was adopted to assess the impacts of the studied treatments from both safety and operation prospective. In the VISSIM analysis, safety performances were measured by using Surrogate Safety Assessment Model (SSAM) developed by the Federal Highway Administration (FHWA). By incorporating the cost-benefit analysis for various scenarios with various bicycle volume levels and traffic volume levels, this study analyzed the conditions that needs bike boxes and the protected intersection.

Results of safety evaluation revealed that the bike box can enhance bicyclist safety by reducing the number of vehicle-bike conflicts. Additionally, bike box can further reduce vehicle-bike conflicts if combined with bicycle signal treatments such as the LBI or EBP. This research also showed that the protected intersection design can be effective in reducing the number of vehicle-bike conflicts and can result in a lower vehicle delay. However, protected intersection design revealed a higher bicycle delay due to the two-stage left turn required for bicyclist to make a left turn. This study also evaluated the cost-effectiveness of these treatment through performing economic analysis. The resulted increase/decrease in delay and saved crashes were converted to monetary values under different traffic and bike volumes combinations to determine if such treatments are cost-effective before actual implementation take place. This revealed the threshold values for traffic and bike volumes that would justify the addition of bike box and the protected intersection treatments. The bike box treatment was found to be effective at traffic volume range of 1086-1231 veh/hr and bike volume of 46 bike/hr. This bike volume level can increase to 92 bike/hr at 1158 traffic volume per hour and the bike box can still be considered advantageous. On the other side, the protected intersection showed a wider range of both traffic and bike volumes where it would be beneficial. It also can be noted that the protected intersection treatment has a higher benefit to cost ratio than that of the bike box. In fact, if we compare these two treatments against each other, the protected intersection design will be more favorable option than the bike box design. Further economic analysis showed that the associated dis-benefits that come from delay increases of implementing bicycle signal treatments such as the LBI and EBP outweigh all benefits that come from saved crashes. Finally, this research created and developed a general guild line with three different facility types that can be used at urban intersection to facilitate bicyclist left turn movements. The developed guideline with the found threshold values of traffic and bike volumes will help the decision makers determine what treatment should be used and when this treatment is most desirable.

Presentation

Final Report