Express toll lanes (ETL) have the advantage of adjusting toll rates dynamically based on the level of toll lane usage. This study developed a microscopic traffic simulation model to evaluate a set of corridor-based tolling strategies for the ETLs located outside-the-beltway (OTB) on an Interstate highway in Northern Virginia using data from 2018. The evaluated toll strategies included dynamic pricing algorithms (DPA) currently implemented inside-the-beltway for the interstate highway under consideration, and several of its variants, as specified by modified DPA parameters and occupancy restrictions. This study also evaluated the performance of the ETLs under different travel demand levels, current and alternative value of time distributions, and potential scenarios when COVID19 travel and business restrictions were eased. A total of 28 scenarios were evaluated for impact analyses.
The changes in vehicle occupancy, mode split, and departure time among travelers were taken into consideration using tolls based on locally collected data from May 2018. The simulation model covered the selected interstate highway corridor from Gainesville, VA to the Washington, D.C. boundary, a few parallel arterials, and other freeways as well as major and minor arterials in the study area. The model included a total of 223 internal zones (centroids), 83 external stations, and 433 signalized intersections. An interactive map-based analyzer from the simulation results was also created to support quick scenario analysis and decision-making.
- The simulation model showed that, compared to traffic conditions before the opening of the OTB ETLs, eastbound travel time along the general purpose lanes improved during the morning peak period by as much as 36.1 percent for the segment near Gainesville.
- Eastbound travel time along the general purpose lanes improved during the morning peak period by as much as 13.2 percent for the segment near Fairfax.
- During the afternoon peak period, westbound travel time improved by as much as 17 percent depending on the segment under consideration.
- The simulation analyses showed that I-66 OTB ETLs were estimated to help improve the traffic throughput of the corridor during the peak hour within the peak period by 20 percent for the morning peak period and 19 percent for the afternoon peak period.
- The simulation analyses also showed that I-66 OTB ETLs did not exert strong adverse impacts on major parallel arterials like US 29 and US 50. The introduction of the ETLs created less than 5 percent impact on the overall traffic volumes along the arterial roads, although the impact during the shoulder hours (e.g., 9 a.m. -10 a.m.) were slightly larger at around 12-16 percent.
- The choice of a DPA played a critical role in maintaining sufficient levels of service at the ETLs. Using the baseline DPA algorithm, currently used inside the beltway, the OTB facility could maintain a speed above the 45 mile/hour threshold, even with higher travel demand and higher value of time distributions tested in this study.
- Higher travel demand and higher value of time among I-66 OTB travelers led to higher numbers of express toll lane users and more toll revenue. The simulation model showed that a 5 percent increase in travel demand could lead to a 15.7 percent increase in the number of OTB users and a 45 percent increase in toll revenue under the baseline DPA algorithm