A World Without Metro, Part 1: I-395 Traffic
Metro’s new strategic planning process, Momentum, articulates a vision for the the next generation of Metro. One way to illustrate Metro’s vital role in the region’s transportation network is to show the impact of not having Metro. This series will give perspective on the many real benefits that Metro conveys to the region today.
Metrorail’s Yellow Line crosses the Potomac from Virginia into DC parallel to I-395’s 14th Street Bridge. Both the rail and highway bridges move large numbers of people into the regional core during the morning rush hour. Between the two inbound spans, the 14th Street Bridge has six lanes. The Yellow Line provides the equivalent of three additional lanes. This math is pretty simple: one lane of freeway traffic can move about 2,420 people per hour (2,200 vehicles per hour times an average auto occupancy of 1.1 people per car) and the Yellow Line moves around 7,400 passengers from Pentagon to L’Enfant Plaza during the peak AM hour. Another way to see it is that the Yellow Line removes 6,700 (7,400 pax / 1.1 pax per car) cars from the road.
What would happen to I-395 if some or all of the in-bound Metrorail Yellow Line customers switched to driving in the morning?
If only 5% of Yellow Line customers drove up the freeway to the 14th Street Bridge during the AM peak hour, I-395 would fill with stop-and-go traffic for ten miles.
Map illustrating regularly recurring three-mile queue and the 10-mile queue that would regularly form if only 5% of the inbound AM commuters on the Yellow Line across the Potomac River switched to driving.
How is this possible?
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