The Seattle Department of Transportation has been performing road diets or road rechannelizations for decades and argues that these projects bring about safer streets without affecting traffic volumes. SDOT collects data on traffic volume, vehicle speeds, and collisions both before and after each project. In a joint effort with Seattle Neighborhood Greenways, I’ve reviewed the studies and found SDOT’s claims to be true as you can see in the key data presented below.
Looking at the numbers, there is some change in roadway volume after the projects, but no consistent pattern that would suggest roadway capacity is being unduly limited. On the positive side, there are significant reductions in aggressive speeding (drivers going 10 miles per hour above the speed limit), including a 93% decrease from the Nickerson St road rechannelization. All collisions are down as a result of these projects and injury collisions have been decreased even further, ranging from a 17% to a 75% decrease.
In short, road diets are a powerful tool the city has to work towards the newly-announced Vision Zero plan.
