Understanding the Safety Impact of Protected Intersection Design Elements: A Driving Simulation Approach

Abstract

Protected intersections are used to facilitate safe crossings for non-motorized users. As a relatively new treatment in North America, it is essential to understand how their design elements, such as bicycle intersection-crossing pavement markings and corner refuge island size, enhance bicyclist safety. A driving simulation experiment was developed to test the effectiveness of different design elements of protected intersections on driver speeds. Participants were exposed to different protected intersection designs that varied with respect to the corner refuge island width and bicycle intersection-crossing pavement marking levels. Their speed at two parts of the right turn, that is, approach and curve speed, was analyzed. A combination of design elements, participant demographics, or bicyclist presence at the intersection affects driver behavior at a protected intersection. The results indicate that the presence of a bicyclist crossing a protected intersection significantly reduces speeds for drivers performing a right turn. Corner refuge islands with larger width were found to reduce speed at the curve as they were accompanied by larger curb extensions which essentially reduce the space for the automobiles. Bicycle intersection-crossing pavement markings influenced only approach speeds prior to the actual turn since that is the location where they were the most visible. Age, gender, and bicycling frequency were observed to affect turning speeds, indicating that design elements alone cannot determine the safety effectiveness of a protected intersection. The findings of this study can guide the implementation of protected intersections.

Investigating the Safety Impact of Segment- and Intersection-Level Bicycle Treatments on Bicycle–Motorized Vehicle Crashes

“…Literature from the Netherlands ( 52 ) as well other recently published guidelines ( 58 ) highlight the need for intersection treatments in addition to segment-level ones. Such countermeasures could be related to control strategies, for example, bike signals, or to more innovative intersection treatments that eliminate points of conflict between bicyclists and motorists, such as the protected intersection ( 53 , 57 ).…”

“…Instead, it recommends additional safety analysis at intersections that feature those treatments, to identify safety deficiencies that may responsible for the high predicted crash frequency. Both treatments increase driver awareness of bicyclists’ presence ( 31 , 53 ) and therefore, should continue being implemented. Bike boxes are effective in placing bicyclists in front of motorized vehicles during the red phase so that bicyclists can remain in front when the green phase starts; they also facilitate bicyclists’ turning movements ( 54 ).…”

Head Start in Time or in Space? Determining Needed Leading Pedestrian Interval Length as a Function of Intersection Layout

“…The results and recommendations of other research and guidebooks for right-turn speed are consistent with this model. A driving simulation study showed that when drivers turn right at protected intersections, whose features include a small turning radius, turning speed at the apex is on average 23 ft/s ( 26 ). The German traffic signals guidelines assume a turning speed of 5 m/s (16.4 ft/s) at signalized intersections when the radius of the inner border of the turning lane is smaller than 10 m (32.8 ft), and otherwise, they assume 7 m/s (23 ft/s) ( 27 ).…”

Examining the Relationships between Multimodal Environments and Multitasking Driving Behaviors

“…In a study conducted by Bella and Silvestri, a driver’s speed choice was shown to be significantly affected by time-to-zebra arrive, which is defined as the time left to the driver to reach the crossing when the pedestrian arrives at the intersection ( 15 ). Deliali et al conducted a study at protected intersections and showed that drivers significantly reduce speed when performing a right turn in the presence of bicyclists ( 17 ). Minhas et al analyzed both site-based and vehicle-based video recordings and showed that driver behavior was two times safer at signalized intersections ( 18 ).…”