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Consider various toll methods to push traffic demand away from peak hours.

The Washington State Department of Transportation’s experience with planning for tolling implementation.

Date Posted

Washington State Comprehensive Tolling Study: Final Report – Volume 2: Background Paper #8: Toll Technology Considerations, Opportunities, and Risks

Summary Information

The comprehensive tolling study conducted by Cambridge Systematics for the Washington State Department of Transportation (WSDOT) set out to provide recommendations to guide Washington as it develops toll facilities in the State. These policies emerged from background research and technical analysis.

The Washington State tolling study describes different types of electronic toll collection (ETC) methods, how they are applied to various toll facilities, note lessons learned from past experiences, and identifies the advantages and disadvantages of each. Furthermore, the study addresses institutional issues relating back office operations and enforcement processes.

The advent of electronic toll collection has provided new tools for traffic management. Manual toll collection's inherent limitations did not provide the flexibility required to use pricing as a means to manage traffic. As a result there are now a variety of methods that may be employed to distribute traffic flow more evenly throughout the day. The lessons presented herein provide an overview of the various methods currently being used.

  • Implement time-of-day tolling as means to push traffic demand away from peak hours. Under this approach, toll rates are fixed by time of day and day of week, usually at one-hour intervals. Peak prices on weekdays are generally highest, and pricing is adjusted typically every few weeks based on hourly volumes. Setting price based on time of day is relatively simple to implement from a technology perspective. This approach is easy for the driving public to understand, but it does not support more frequent updates to pricing, as rate schedules are generally published. The concept is relatively easy to convey to the public through publicizing the schedule.

    Both the New Jersey Turnpike and the Port Authority of New York and New Jersey introduced time-of-day-based-toll price schedules during toll increases over the past several years. The Turnpike Authority reports that traffic growth during rush hours has flattened since it adopted the time-of-day-based toll schedule. Port Authority reports also suggest that relatively lower prices attract some motorists to off-peak driving times.
  • Use dynamic pricing, based on current conditions, to shift traffic demand. Dynamic pricing adds a level of traffic management sophistication over time-of-day pricing. With dynamic pricing, tolls are based on actual traffic conditions, changing to maximize some specific objective. Typical traffic management objectives are:
    • Speeds – A classic measurement of the conditions on a facility, is easily collected using available sensor technologies, and is easily understood by the public. It also allows for frequent pricing adjustments based on changing conditions. However, speeds can vary greatly across a facility, particularly between differing sensor sites, and are not always an effective measurement of true level of service. Speeds are generally best used in conjunction with volume and/or occupancy to allow more accurate setting of prices.
    • Volumes – Can be averaged over time to support less frequent pricing changes, or they can be used together with speeds to set prices on a more frequent basis. Volumes can be relatively accurately measured with existing sensor technologies.
    • Traffic Density – A measure of speed and volume over a set period of time, and is considered a very accurate measure of actual level of service. Use of traffic density has been proposed for several High-Occupancy Toll (HOT) lane facilities. Its disadvantages include that it requires greater sensor accuracy and reliability, and it is difficult for the driving public to understand when compared with other measures.
    • Travel Time – Perhaps the truest measure of value to drivers, travel time also can be the most difficult to measure. Travel times can be collected from transponder equipped vehicles by matching transponder identification numbers at two points. Travel times can also be estimated based on speed/volume sensors placed at regular intervals along the facility with calibration based on less frequent radio frequency tag reads.

    Regardless of the measure used, high levels of accuracy are crucial. Generally, existing field traffic sensor infrastructure needs to be updated to properly support dynamic pricing. Existing infrastructure has generally been deployed for traffic management and monitoring purposes where occasional failure of individual sensors does not drastically impact the overall effectiveness of the system. However, with toll systems, high accuracy and reliability of greater than 99 percent are necessary to ensure accurate toll rates and to maintain public confidence. The tighter the frequency or greater the number of segments, the more important accuracy and reliability becomes.

  • Include High Occupancy Toll (HOT) lanes to alleviate peak hour congestion. HOT lane facilities charge Single-Occupant Vehicles (SOV) for the use of a High-Occupancy Vehicle (HOV) lane. Access into the HOT lane remains free for transit, vanpools, and carpools. The toll charged for SOVs is dynamically adjusted to ensure traffic congestion does not exceed an established threshold for all vehicles in the HOV lanes. Toll collection is done electronically to provide nonstop toll collection. Tolls are charged at fixed points along the facility.

As peak hour congestion continues to be a problem throughout the United States, agencies are looking towards tolling technologies as a mitigation technique. Varying tolls based on the time-of-day and/or current traffic conditions allows agencies to shift traffic demand away from normal peak hours; resulting in a more effective traffic management process. The advent of HOT lane facilities provides the option for drivers, willing to pay a premium, to experience less congested travel, creating great traffic distribution across road networks.