4329
Modeling Roundabout Traffic Flow as a Dynamic Fluid System
Abstract
With increasing usage of roundabouts as traffic control mechanisms, it is important to
develop a criteria for the design of e fficie nt roundabouts. We designate vehicle throughput
as the primary measure of a roundabouts efficiency and delay experienced by vehicles
as a secondary measure. We then apply a fluid flow analogy to model traffic density
and throughput within an arbitrary roundabout system with any number of incoming
traffic streams. Due to the distinct differences that separate one-lane roundabouts from
two-lane or multi-lane roundabouts, our model considers each lane case separately and
determine which case is optimal for a given flow of traffic. The model describes the
roundab out system as a non-linear first order partial differential equation relating speed,
traffic density, and traffic flow, all of which are subject to physical constraints. The
model is able to evaluate how many lanes are needed, and whether traffic light controls are
necessary for a given roundabout system. As real-world case study, we apply our model to
a roundabout intersection in Alachua Country Florida, and suggest optimal parameters
to maximize traffic flow through the roundabout. Applying our model to a variety of
roundab out scenarios led us to the following conclusions: traffic lights should not be used
at roundabouts; increasing the radius of the roundabout will increase the throughput,
but the effect is only significant at high rates (above 0.25 vehicles per second per entering
road) of traffic; increasing the number of lanes will always increase throughput, but the
benefit only becomes significant when traffic is heavy; increasing radius increases delay for
vehicles entering at speeds above 20m/s, while decreases delay for those entering below
20m/s.
