Lateral Placement of Motor Vehicles When Passing Bicyclists

This study assessed the lateral placement of motor vehicles as they passed bicyclists, with a focus on the influence of centerline rumble strips. Driver behavioral data were collected through field studies on two segments of a high-speed (55-mph speed limit) rural two-lane highway. The study segments were similar for key traffic and geometric characteristics, but only one of the segments had centerline rumble strips. The segments were located close to one another; this feature ensured a relatively uniform sample of drivers and bicyclists. Centerline rumble strips were found to decrease the likelihood of a motor vehicle driving onto the center line. However, this decrease in the probability of centerline encroachment was less pronounced in comparison with similar data collected in the absence of bicyclists; this increased probability of encroachment suggests a compensatory effect. Drivers were also more likely to contact or cross over the centerline when bicyclists were nearer to the travel lane. The type of motor vehicle also played a role in that motorcycles and passenger cars were less likely to contact the centerline, and the presence of opposing traffic was found to reduce the likelihood of contact with the centerline.