United States Department of Transportation
i
A self-adaptive toll rate algorithm for high occupancy toll (HOT) lane operations.
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2009-12-01
[PDF-1.27 MB]
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Edition:Final report.
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Abstract:Dramatically increasing travel demands and insufficient traffic facility supplies have resulted in severe
traffic congestion. High Occupancy Toll (HOT) lane operations have been proposed as one of the most
applicable and cost-effective countermeasures against freeway congestion. By allowing Single Occupancy
Vehicles (SOVs) to use High Occupancy Vehicle (HOV) lanes with a toll, excess capacities of HOV lanes can
be utilized. Through balancing pricing and vehicle occupancy constraints, an HOT lane system can optimize
traffic allocations between HOT and General Purpose (GP) lanes and hence enhance the overall infrastructure
efficiency if a proper tolling strategy is employed. Although there exist several tolling strategies, two major
problems with these tolling strategies may significantly degrade the HOT lane system performance. First, the
under-sensitive tolling algorithm is incapable of handling the hysteresis properties of traffic systems and may
cause severe response delays. Secondly, unfavorable flow fluctuation on both HOT and GP lanes may result
from over-sensitive tolling strategies and generate agitating traffic operations.
To address these problems, a new self-adaptive dynamic tolling algorithm is developed in this study to
optimize HOT lane operations. To reduce the computational 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 feedback control theory. Then the appropriate toll rate is
estimated backward using the discrete route choice model. To examine the effectiveness of the proposed
tolling algorithm, simulation experiments were conducted. A microscopic traffic simulation software tool,
VISSIM, is utilized. The proposed algorithm is implemented and integrated with the VISSIM package through
an external module specifically developed for this study. Data from the Washington State Route (SR) 167
HOT lane system is used to build and calibrate the simulation model. The simulation experiment results show
that the proposed tolling algorithm is capable of responding to traffic changes promptly and effectively. It
performed reasonably well in optimizing overall traffic operations of the HOT lane system under various
traffic conditions. This algorithm is logically straightforward and not difficult to implement.
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