Abstract :
This thesis addresses the most important elements of capacity evaluation and operational performance of
roundabout traffic intersections in Visakhapatnam on capacity analysis movements of the vehicles were
observed at 5 roundabouts. Gap acceptance and follow up time were estimated for cars for one hour
analysis. The relation between a roundabout performance measure and capacity is expressed in terms of
degree of saturation (volume – Capacity ratio). The capacity analysis is done based on gap acceptance
method that is adopted by Tanner based on the HCM 2010. The traffic movement data with vehicles
characteristics were collected from 5 roundabouts in Visakhapatnam. These 5 roundabouts are directly
related to their approach leg numbers.
Approach entry capacity has been analysed for all 5 roundabouts at their legs. Effective capacity verses
entry flow relationship have been developed in order to find out the causes of their over saturation (v/c ratio
greater than 0.85) And the result indicates; number of entry lanes, number of circulatory lanes and high
traffic flow are the major causes of their over saturation.
Tanner models use the gap-acceptance theory (or critical headway) to simulate the behaviour of entering
vehicles and vehicles circulating within the roundabout. Finding a safe gap (or headway) with circulating
traffic stream to enter the roundabout is the control variable that determines the ability of approach vehicles
to enter the roundabout. Current research work on roundabout models mostly concentrates on determining
the capacity of an approach based on the entering and circulating flows. Approach capacity is calculated as
a mathematical function.
Keyword :
Roundabout, capacity, Gap Acceptance, Follow up time, Delay, Queue length, LOS, Degree of saturation.