LATERAL CLEARANCE BETWEEN VEHICLES AND BICYCLES ON URBAN ROADS

The clearance motorists allow when they overtake bicyclists is critical to the safety and level of service experienced by bicyclists in mixed traffic. Recent calls for mandatory minimum lateral clearances in South Africa indicate its importance to the bicycling and sustainable transport communities. This study reports on locally measured lateral clearances between bicycles and vehicles on urban roads in Tshwane. An ultrasonic device was used to measure passing clearances under varying traffic and roadway conditions, and the paper reports on the range and variability of the observed clearances. A regression analysis was performed to identify the factors affecting lateral clearance, such as lane width, vehicular speed, and density. Guidance is offered around the combination of vehicle volume and lane width that can be expected to result in given levels of bicycle safety. This guidance might help practitioners to identify pro-actively roadways with high accident potential for cyclists, or to identify suitable roads for inclusion in an areawide safe bicycle network.