The Airtight Case for Road Diets

Bill Lindeke at Streets.mn calls them “death roads.” Four-lane roads in urban areas can indeed be perilous.

An 11-year-old boy was struck by a motorist on one of these roads recently in St. Paul. The media and others responded in typical fashion, deeming the crash an unavoidable “accident.” But the truth is these types of collisions are easy to prevent, Lindeke says.

Converting four-lane roads to three lanes, a change commonly known as a “road diet,” makes them substantially safer, with little downside. Lindeke cites the data.

#1) 3-lane roads are much safer for car drivers. According to a Federal Highway Administration study, changing a 4-lane Death Road™ into a three-lane road reduces automobile traffic accidents from 20% to 50% depending on the context. (Note: this makes intuitive sense if you’ve ever driven on a street like this.) There are dozens of similar studies out there.

#2) 3-lane roads have marginal impact on traffic flow. I’m not going to suggest that a 4-to-3 conversion of a Death Road™ has no impact on traffic flow (though sometimes that turns out to be the case). Rather, fixing a Death Road™ usually sees a reduction in car throughput in the 5% to 10% range. As another Federal Highway Administration report puts it, “under most average daily traffic (ADT) conditions tested, road diets have minimal effects on vehicle capacity.”