High Occupancy/Toll System in Northern Virginia Improves Both Travel Time and Travel Time Reliability.
A Study of the I-66 Tolling System outside Washington, DC
Made Public Date

Virginia, United States

Fairfax County: Virginia,
United States

Investigating the impacts of I-66 Inner Beltway dynamic tolling system

Summary Information

I-66 is a major east-west highway that connects downtown Washington D.C. to Northern Virginia. Since it is the only major east-west highway between D.C. and the populous Virginia suburbs, I-66 experiences heavy traffic congestion especially during peak hours.

To alleviate congestion, public authorities initially implemented peak period High Occupancy Vehicle (HOV) restrictions along the portion of I-66 inside the I-495 beltway. In 2017, the Virginia Department of Transportation (VDOT) altered the restrictions on this I-66 segment and switched from HOV to High Occupancy/Toll (HOT) lanes. After the change, users can access the lanes during peak periods by paying a toll, which is dynamically set based on demand, or by having multiple people in their vehicle.   

A research group at University of Maryland studied the effects of HOT tolling on the I-66 corridor. The team first gathered a robust mix of data sets such as toll data, probe speed data, and traffic volume data. Critically, the team studied traffic conditions both on the toll lanes themselves and on alternative, non-tolled roads, such as US Route 50 and the George Washington Memorial Parkway.  Then the team performed statistical analysis of the traffic corridor before and after HOT implementation.

The team found:

  • Travel time and travel time reliability (in terms of median and 95th-percentile travel time) improved after HOT lane implementation both on I-66 itself and on nearly all non-tolled alternative routes studied. 
  • These findings demonstrate that toll lanes can be an effective means of improving traffic conditions along a travel corridor and has been more effective than HOV lanes in spreading travelers' departure times.
  • Analysis of the estimated value of time during each 6-minute toll interval ranged from $10 to $300 per hour, with a median value of $70 per hour.
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