Abstract: 

This paper studies the capacity of a highway with an on-ramp, using a cellular automaton (CA) model. This CA model is in the framework of three phase traffic theory and can reproduce the first order phase transition from the free flow to synchronized flow (Jiang and Wu, 2005, European Physical Journal B, 46, 581-584). It is shown when some special homogeneous boundary conditions are used, the capacity of the on-ramp system is greatly enhanced because the strong interactions of main road vehicles and on-ramp vehicles, which occur under inhomogeneous boundary conditions, are avoided. Based on this finding, we propose a new design of road section upstream of on-ramp, i.e., to split the main road into several branches and then the branches merge together. With the help of traffic light control, the inhomogeneous vehicles are homogenized. Accordingly, the capacity is enhanced.