Evaluating Roundabout Capacity, Level of Service and Performance

Aerial photograph of road


This paper discusses various findings and recommendations of the NCHRP Report 572 on roundabout capacity and level of service. Discussions include issues related to the finding of lower capacity of roundabouts in the USA compared with Australian and UK roundabouts, and the choice of Level of Service (LOS) thresholds for roundabouts compared with those used for signalized and sign-controlled intersections. Capacity and the resulting degree of saturations (v/c ratio) estimates obtained using the NCHRP Report 572 and standard SIDRA INTERSECTION methods are compared by presenting single-lane and multi-lane roundabout examples. Importance of the basic findings of research on US roundabouts as presented in the NCHRP Report 572 is discussed. Various model extensions related to the use of the NCHRP 572 model in SIDRA INTERSECTION are discussed. An example is also given for modelling Roundabout Metering signals. Finally, the paper presents a discussion of the issue of possible increases in roundabout capacities in the USA over time due to changes in driver behaviour.


AKÇELIK, R. (2009). Evaluating Roundabout Capacity, Level of Service and Performance. Paper presented at the ITE 2009 Annual Meeting, San Antonio, Texas, USA, Aug 2009.