The Use of Hard Shoulders as a Turning Lane: A Safety Evaluation

Abstract

This paper investigates the phenomenon of South African drivers using the hard shoulder of the road as an unofficial turning lane. Due to the increasing number of vehicles on our roads, drivers often experience heavy congestion during the peak hours of the day. A growing trend has emerged in the Western Cape of drivers using hard shoulders in advance of a left turn; essentially creating an informal turning lane to reduce travel time by bypassing the traffic queues. The paper represents an initial safety evaluation of this phenomenon along the R44 between Stellenbosch and Somerset West, and also an attempt to identify geometric and traffic flow conditions common to a number of intersections where this phenomenon is observable. It examines the operating circumstances under which road users appear willing to use the road shoulder, specifically the physical dimensions of road elements and the speed differentials between vehicles travelling in the road shoulder and those of the adjacent lane. It looks further at the interaction between non-motorized transport and motorized transport and measures conflicts between road users that occur as a result of these manoeuvres. The results failed to find any measurable relationships between road geometry and the emergence of the use of a hard shoulder preceding an intersection, suggesting that the physical design of the intersection is not, in itself, necessarily a contributory factor of this behaviour. However, the conflict analysis showed clearly that conflicts with pedestrians and cyclists are certainly evident when hard shoulders are being used by turning vehicles, and that intersection design currently does not offer sufficient protection for non-motorised traffic at these intersections. A sufficiently high number of conflicts was recorded to suggest that these manoeuvres could result in injury crashes in the future, unless thought is given to either preventing this behaviour, or protecting users more rigorously.