Quality of Service (QOS) of Urban Roundabouts: A Literature Review

Abstract: Nowadays roundabouts have been a widespread design solution, in urban and rural areas, mainly due to their efficient traffic control and their safety performance. They provide several advantages in comparison to signalized and stop-controlled intersections. While there is generally acceptance by researchers that roundabouts create operational and safety benefits, their acceptance by the general public is not at the same level, as past research has demonstrated strong public sentiment against roundabouts. The Highway Capacity Manual (HCM2010), describes specific techniques to evaluate the traffic handling ability of a transportation facility of roundabouts through measuring the Level of Service (LOS). It also introduces the concept of Quality of Service (QOS) to assess the perceived performance of the transportation facility from the viewpoint of drivers and travelers. It has been assumed that both LOS and QOS are interacting equally to roadway operating agencies, transportation engineers, and other decision makers. The paper presents basic characteristics of a modern roundabouts. The clarification of the definitions of QOS and LOS of roundabouts is also presented and a review on the recent published research related to LOS and QOS of urban roundabouts is being carried out. Through this review, the authors intend to identify the factors affecting the two indexes. Moreover, in this paper a number of surveys through questionnaires about public opinion on roundabouts is reviewed and their results of "before and after" analysis are presented