Phase diagram of a single lane roundabout

• Simulations are conducted to study the characteristics of traffic flow at a single-lane roundabout with/without splitter islands.
• Phase diagrams for roundabout are constructed.
• The effect of the system size, aggressive entry, and the probability of preferential exit are discussed.

Using the cellular automata model, we numerically study the traffic dynamic in a single lane roundabout system of four entry/exit points. The boundaries are controlled by the injecting rates α1α1, α2α2 and the extracting rate β  . Both the system with and without Splitter Islands of width LspLsp are considered. The phase diagram in the (α1,βα1,β) space and its variation with the roundabout size, PaggPagg (i.e. the probability of aggressive entry), and PexitPexit (i.e. the probability of preferential exit) are constructed. The results show that the phase diagram in both cases consists of three phases: free flow, congested and jammed. However, as LspLsp increases the free flow phase enlarges while the congested and jammed ones shrink. On the other hand, the short sized roundabout shows better performance in the free flow phase while the large one is more optimal in the congested phase. The density profiles are also investigated.