摘要：Abstract:Freeway congestion in many cases may spill back for several kilometers, blocking a number of on/off-ramps upstream of the congestion origin. As a result, the total off-ramp flow may substantially reduce, and vehicles bound for the blocked off-ramps are trapped in the mainstream congestion, causing the continuing spillback of congestion that blocks more off-ramps at the further upstream with similar effects and so forth. The off-ramp blockage effect is readily understood and its impact is empirically recognized, but there is a lack of analytical results to provide more insights. In this paper some flow conditions on bottleneck activation are first established, and the mechanism of the off-ramp blockage is theoretically explored. Macroscopic and microscopic simulations are conducted to demonstrate the analytical results obtained. To demonstrate the off-ramp blockage effect in particular, general relations between the total demand, total inflow, total off-ramp outflow, and the number of vehicles within the considered freeway system is examined in simulation. This work can shed some light on a side of traffic network dynamics that was not given enough attention before.
