Study of speeds in relation to the geometric design of roundabouts

Abstract

“Since the beginning of the Twentieth century, roundabouts have been applied with more frequency” (Slavko Davidovic ́, 2020). The roundabout was created to lessen the traffic by following the give-way rule, which prevents circular crossings from blocking by withholding vehicle entry until there are enough breaks in the flow of traffic. The performance assessment of the roundabout is based on a few parameters such as capacity, degree of saturation, speed, delay, and geometry. Analysing the available literature revealed that previous studies emphasise speed as one of the most important parameters in roundabout geometrical shaping, also it was proved that the geometry of a roundabout impacts speed. As we know “Speed is a parameter of traffic flow (functionality and quality of roundabout) accordingly Speed is impacting the performance of the roundabout” (Slavko Davidovic ́, 2020). The change in geometry and speed led to a great change in its performance. As per IRC code, “Roundabouts operate at speeds lower than that of the network preceding and succeeding it as it requires to give way behaviour and gap acceptance” (IRC:65, 2017). Generally, vehicles are expected not to run more than 30 and 40 km/h around urban and Rural roundabouts respectively. This Study intends to study the speeds at roundabouts of different radii to understand the performance of a roundabout with the speeds collected at approach entry, circulating space, and exit of the roundabout using the spot speed method to explore where exactly on roundabout vehicles will slow down and these radius change will influence Speed. The outcome will be the relation between speed and geometry, as the geometry impacts the speed and maximum, and minimum speeds practised at the roundabout. Further, it studies the possible methods to maintain the speeds at roundabouts.