The Airtight Case for Road Diets

#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.”

#3) 3-lane roads slow speeds. The main difference between a 4-lane Death Road™ and a 3-lane safe street is that traffic speeds go down and become far more uniform. It’s a proven fact that reducing speeds even a little bit, i.e. from 40 to 30 miles per hour, can make a huge difference on accident severity for pedestrians and bicyclists.

#4) 3-lane roads increase biking and walking. After a 4-lane Death Road™ was fixed in San Francisco, “bicycle usage increased 37% during the PM peak hour,? the number of pedestrians increased 49% during the PM peak hour, [and]? public response has been overwhelmingly positive about this project.” That’s just one example; also, it’s common sense.

#5) Fixing a Death Road™ is really cheap. Unlike expensive street reconstructions or concrete bumpouts, cities and counties can quickly, easily, and cheaply fix these Death Roads™.