The Impact of Phase 1 of the Silver Line on the Northern Virginia Transportation System

About the report:

The purpose of this study was to assess the impact of Phase 1 of the Washington Metropolitan Area Transit Authority’s Silver Line on the broad regional transportation system, and specifically on the road network operated by the Virginia Department of Transportation (VDOT). All of the data used in this study were aggregate and were provided by transit agencies and VDOT.

The study used geographic information systems to visualize transit demand and regression and the Mann-Whitney U test to identify patterns, estimate new transit demand, and determine whether road changes were significant. Some, but not all, Silver Line ridership appeared to be drawn from the Orange Line, resulting in traffic pattern changes between the two lines. This finding was supported by the ridership on the two lines and changes at intersections in the south of Reston and intersections near the West Falls Church Metro Station.

The regression analysis showed that the Silver Line attracted approximately 20,000 new rider trips (trip ends counting both exits and entrances separately) on a typical weekday. Ridership at the Wiehle-Reston East Station showed a strong pattern of commuting traffic, with a detectable morning and afternoon peak for entries and exits, respectively. Changes in the intersection counts in Reston supported this pattern. However, the numbers of entries and exits during the same time period for the other four stations were more balanced. Ridership supported reverse commuting with the Silver Line. Some mode or route shifts appeared to occur in the Reston area, suggested by improved travel times on VA-267 between Route 28 and Hunter Mill Road in the AM peak and in the Tysons Corner area, suggested by improved travel times on I-495 between I-66 and Route 7 and intersection count changes at Chain Bridge Road and International Drive. Another travel pattern shift in the Tysons Corner area appeared to be the avoidance of the interchange of Route 7 and Chain Bridge Road, particularly suggested by changes at the intersection just west of this interchange. The majority of the road data suggested general growth in the region, which hid some of the benefits of the Silver Line. The new ridership allowed for some accommodation of new traffic and traffic rebalancing across routes.

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