PlanItMetro

The Silver Line will relieve traffic congestion on the Dulles Toll Road and I-66 when it opens in 2014.

This post is a continuation of our series that answers questions about the new Silver Line.

It’s no secret that the Washington region has some of the worst traffic in the country.  Listeners to “drive time” radio are bombarded with rapid-fire traffic reports noting congestion on major regional highways, often caused by “nothing but volume”.  This expression means there is no traffic accident, weather incident or excessive sunshine slowing cars down.   Instead, too many cars are trying to squeeze into too few lanes at critical interchanges, resulting in traffic queues that can extend for miles and miles.

Not surprisingly, the highways along the Silver Line corridor are some of the region’s most congested. The merging of I-66 and the Dulles Toll Road was ranked fourth worst congested location (PDF) in the MWCOG Spring 2011 Traffic Survey.  The survey showed the toll road has three major congestion spots in the AM Peak:  the toll plaza, the interchange with the Capital Beltway and the merger with I-66.  In all three cases, the recurring congestion was caused by vehicles weaving and merging.

Surveyed morning traffic conditions on the Dulles Toll Road, from the MWCOG 2011 Traffic Survey. Image links to PDF report.

According to the MWCOG report, the speed in the traffic queue is between 20 and 50 MPH.  This would result in between 2 and 12 minutes of delay per vehicle joining the back of the queue heading to the toll plaza. Assuming a duration of 2 hours for the queue, average vehicle occupancy of 1.1 and 1,900 vehicles per lane per mile, this results in between 560 and 3,300 person-hours of delay per day, up to 840,000 person hours per year. Read more…