Research on bottleneck effect of tunnel in steep uphill of city highway

In the steep uphill area of a tunnel in the city highway, because of the brightness environment coupled with gravity causes the drivers slowing down the speed unwarily. This will makes the average speed of vehicles reduce. Based on METANET model shows that this section can be equivalent to reducing lane bottleneck road, with traffic flow increases, the degree of congestion has catastrophe. The simulation by vissim and the data analysis by matlab shows that when less traffic on road, such bottlenecks have much smaller impact on traffic flows, and when traffic flow increases, this will cause serious traffic congestion suddenly. Meanwhile the bottleneck effect of steep uphill in tunnel has relationship with the proportion of vehicles which have significant reduction of the speed.