Framework model for time-variant propagation speed and congestion boundary by incident on expressways

For the purpose of accurately capturing the evolution characteristics of the congestion on urban expressways under traffic incidents, this study developed a framework model for the time-variant propagation speed and congestion boundary based on shockwave model. An initial analysis demonstrated that the traffic demand and facility supply determine the propagation speed and boundary. The outflow at the incident section was considered, which is affected by the number of closed lanes, the proportion of buses, and the number of lane-changing vehicles. Additionally, the background demand varies with the time of day and the location due to a high density of ramps. The entry and exit flows of on-ramps and off-ramps under the traffic incident were shown to have a considerable impact on the congestion propagation. Consequently, the framework model was developed and parameters were estimated based on the field data of ring-road expressways in Beijing. For practical purpose, the data inputs were provided by the floating car system and remote traffic microwave sensor system. Three incidents on expressways were adopted to evaluate the capability of the model. Results showed that the proposed model is able to practically model the time-variant characteristics of the propagation speed and congestion boundary of traffic incidents.