Dramatically increasing travel demands and insufficient traffic facility supplies have induced severe traffic congestion. High Occupancy Toll (HOT) lane operation has been proposed as one of the most applicable and acceptable countermeasures against freeway congestion. By balancing demand and toll, HOT lane operations can be optimized and overall infrastructure efficiency can be enhanced. However, few previous studies have concentrated on optimal tolling strategies. Two major problems with inferior tolling strategies are known to degrade HOT lane system performance. First, an under-sensitive tolling algorithm is incapable of handling the hysteresis properties of traffic systems and may cause severe delay in response. Secondly, unfavorable flow fluctuations on HOT and GP lanes may be generated due to an over-sensitive tolling strategy. To address these problems, the paper develops a new feedback-based tolling algorithm to optimize HOT lane operations. To decompose the calculation complexity, a second-order control scheme is exploited in this algorithm. Based on traffic speed conditions and toll changing patterns, the optimum flow ratio for HOT lane utilization is calculated using the feedback control theory. Then an optimal toll rate is estimated backward using a discrete route choice model. This algorithm is simple, effective, and easy to implement. VISSIM-based simulation tests were conducted to examine its practicality and effectiveness. The test results show that the proposed tolling algorithm performed reasonably well in optimizing overall traffic operations under various traffic conditions.
Abstract