Traffic flow characteristics of bottleneck segment with ramps on urban expressway

The traffic flow characteristics and drivers' behavior between an on-ramp and off-ramp segment are mainly investigated by empirical research. The field data is obtained by the video camera and Metrocount 5710 located at the eastern of Haidian Bridge of Beijing's Fourth Ring Road. From data analysis, it is revealed that the capacity is dropped and a bottleneck is formed on the main road when the on-ramp inflows are larger than a certain threshold. It is also shown that the merge inflows and main road discharge flows have some mutation characteristics. It means that when the on-ramp merge inflows are larger than a certain threshold, there will be capacity drop at shoulder lanes of main road. In addition, when the off-ramp is oversaturated, the queue will block on-ramp vehicles and occupy shoulder lanes of main road. It results in capacity decrease in the segment. Meanwhile, although the density is same before and after the formation of the queue, the velocity of the third lane obviously decreases. Copyright ASCE 2009.