When Do Drivers Yield to Cyclists at Unsignalized Roundabouts?

Abstract

Cycling has grown in popularity during the past decades in many cities in Europe and in the United States 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 a lack of evidence and of analysis of what happens in such interactions. This paper explores empirical evidence of vehicle–bicycle interactions on a typical Swedish roundabout and provides insights into factors that influence car drivers' yielding decisions when they interact with cyclists. Vehicle–bicycle interactions were divided into groups (nonconflict, conflict, yield, and nonyield), 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 compared with bicycles, which exhibited smaller variation across groups. The modeling results revealed that the probability of yielding decreased when the speed of the vehicle was higher. But a bicycle's speed had little effect on a driver's decision to yield. More important, the probability of yielding was increased significantly by the proximity of the cyclist to the conflict zone. The yielding rate of drivers can be improved by keeping vehicles' speed to less than 20 km/h, as drivers then have the capacity to detect and yield to cyclists.