This paper describes a way of including entry ramps in the Nagel-Schreckenberg traffic model. The idea is to place what are called shadow cars on a highway next to cars on entry ramps, which enables the drivers to take ramp cars into account. The model is shown to capture important real-life traffic phenomena that have not been included in previous models. Furthermore, it is demonstrated that the desirable properties of the Nagel-Schreckenberg model are retained.
Physical Review E (statistical, Nonlinear, and Soft Matter Physics), 2002, Vol 65, Issue 5 Pt 2