A Feedback-Based Dynamic Tolling Algorithm for High-Occupancy Toll Lane Operations

Dramatically increasing travel demands and insufficient traffic facilities 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. With balanced pricing and vehicle occupancy constraints, HOT lane operations can realize the optimal traffic allocation and enhance overall infrastructure efficiency. However, few previous studies have concentrated on optimal tolling strategies. Two major problems with inferior tolling strategies degrade HOT lane system performance. First, an undersensitive tolling algorithm is incapable of handling the hysteretic properties of traffic systems and may cause severe response delays. Second, oversensitive characteristics of imperfect tolling strategies may cause unfavorable flow fluctuations in HOT and general-purpose lanes that disrupt traffic operations. A new feedback-based tolling algorithm to optimize HOT lane operations addresses these problems. To decompose the calculation complexity, a second-order control scheme is used in this algorithm. On the basis of traffic speed conditions and toll changing patterns, the optimal flow ratio for HOT lane use is calculated by using feedback control theory. The appropriate toll rate is then estimated backward by using the 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. Test results show that the proposed tolling algorithm performed reasonably well in optimizing overall traffic operations of the HOT lane system under various traffic conditions.