In this research, the benefits from saving travel time through the use of toll rates that vary by lane are investigated. Variable travel time (VTT) distributions were used to investigate the possible benefits of different toll rates versus a uniform toll rate for a roadway. In the differential toll rates strategy, the roadway was divided into cheap, moderate and expensive lanes. In the uniform toll rates strategy, all lanes had the same toll rates (which could also be free).
Drivers on the Katy Freeway in Houston (an existing managed lanes facility) provided travel time information via an Internet survey. The dataset was acquired and sorted by driving scenario (normal demand and five scenarios where demand increased) as well as income level of the vehicle operator, resulting in 18 distinct subsets. Using VTT distributions developed by Patil et al. (1), travel delay and travel time metrics were calculated using a function that incorporated free flow travel time, total lane volume, and lane capacity. The value of travel time was then computed for each of the 18 subsets of drivers. Several experimental results were produced by modifying the facility volume (between 7,000 and 9,500 vehicles per hour) and the percentage of trips deemed "urgent," with a larger percentage indicating increased VTT.
The calculations of the research team resulted in the following VTT benefits:
- 12.72 percent maximum VTT savings benefit (9,500 vehicles per hour, 30 percent urgent trips).
- 1.45 percent minimum VTT savings benefit (7,000 vehicles per hour, 10 percent urgent trips).
- VTT savings benefits between 1.88 percent and 10.86 percent for 13 intermediate scenarios.
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