Michael sent along this amusing “FAIL” photo… but is it really a fail at all?

Image from FAIL Blog.

At first blush, this looks ridiculous. How can closing a lane ease congestion? But actually, it can.

Let’s say you have a road that’s one lane in each direction. At one spot, it turns into 2 lanes each direction, then back to 1. What will happen?

People will speed up when the road widens, then merge back where it narrows. Merging creates “friction,” forcing drivers to slow down a little more than usual and to wait for each other which can be inefficient. The end result is lower throughput overall than if the road simply stayed one lane.

This exact thing happens on the Clara Barton Parkway. There’s an area just outside DC with exactly this geometry. The parkway might flow well until that point, yet during periods of moderate traffic there’s always congestion right at the merge.

Sometimes an extra lane is worthwhile. Many mountain interstates widen to provide climbing lanes for large trucks, for instance. But the Clara Barton Parkway is not such a situation (and doesn’t allow trucks, anyway).

For a short time I had to drive to Potomac in the evening rush periodically, and always wondered why this bizarre situation still existed. If the parkway simply remained one lane each way with the other closed, it would indeed ease congestion.

Maryland narrowed Bradley Boulevard in Bethesda around where it crosses the Beltway. The road, usually 2 lanes each way, widened to 4 and then narrowed again. Now, 2 whole lanes are marked off with stripes. That smooths traffic and also gives bicycles and pedestrians a better shoulder to use when connecting between neighborhoods on either side.

Bradley Boulevard. Image from Google Maps.

As for the FAIL Blog photo, that was on a highway in Cornwall, England in 2006. Huge numbers of drivers were descending on the region for a music festival, and officials recognized that a 2-mile passing lane would actually worsen traffic with the heavy load.

It may sound barmy but in fact it makes a lot of sense because, if it was left open, traffic from the two lanes would have to merge into one at the top. This causes a lot of aggro and a lot of stopping and starting which has been shown to delay traffic even more.

How about cutting down on the “aggro” on the Clara Barton as well?

David Alpert is Founder and President of Greater Greater Washington and Executive Director of DC Sustainable Transportation (DCST). He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle. Unless otherwise noted, opinions in his GGWash posts are his and not the official views of GGWash or DCST.