Nowadays, traffic congestion at intersections has become a severe problem in urban transportation systems. It not only causes large-scale delay in road network but also increases accident frequency. As an alternative solution, overpass system has been introduced. However, this system obviously has very high complexity, resulting in a long construction period and high cost.
Being aware of the current problem, we started to look into the cause of it. It is mentioned in previous literature that left turns have negative impact on transportation systems. Left turn vehicles have potential to crash with oncoming vehicles, and usually wait for longer time, and thus left turn prohibition (LTP) has been adopted as a possible solution in order to overcome the mentioned issues. Another analysis perspective is from the reduction of conflict points, when all left-turn directions are forbidden, the number of conflict points can be reduced from 16 to 4 compared with no LTP measure.
In our simulation, we built a model on PTV VISSIM using the real-world traffic data and road network of Hell’s Kitchen, Manhattan. Two parameters: total number of vehicles possessed by the network and maximum delay were analyzed. The results shows that LTP intersection can improve the system performance and relieve congestion to some extent. However, during rush hours, congestion still happens even in the LTP system.
So here is our ultimate solution: we can use LTP to reduce conflict points from 16 to 4. Meanwhile, we can build bridge at intersection to eliminate the remaining 4 conflict points caused by vehicles going straight from upright directions. We proposed different solutions for various types of intersections, including the most typical cross intersection, T intersection and five-way intersection.
In order to examine the effectiveness of our new proposed system, we updated our VISSIM model: while maintaining LTP for the entire road network, we changed all normal intersections on a certain road into bridge intersections. Using this model we did another simulation and it proved LTP-bridge intersection could bring significant positive effect to the whole network.