The availability of pedestrian gaps and the queuing effects of pedestrian crossings have implications for roundabout design, particularly when considering the operations of roundabout exits and the potential for vehicle queues to spill back onto the circulatory roadway. In most jurisdictions, vehicles are required to yield to pedestrians. In practice, pedestrians often choose their crossings to coincide with gaps in the traffic stream, i.e., yielding to vehicles. This paper presents methods to analyze both conditions. In the case where pedestrians yield to vehicles, the minor-street movement capacity equations from the Highway Capacity Manual's unsignalized intersection methodology can be adapted to determine the number of gaps in a traffic stream sufficient for a pedestrian to cross. In the case where vehicles yield to pedestrians, the effect of a vehicular queue extending into the roundabout while waiting for pedestrians to cross can be estimated, and the extent to which this queue will adversely affect capacity can be approximated. The paper concludes by discussing the implications of the interactions between pedestrians and vehicles on the design of the roundabout.
Abstract