Road Diet Data: Studies show projects lead to safer roadways

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.

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3 Responses to “Road Diet Data: Studies show projects lead to safer roadways”


  • Troy – Why are you using “road diet”? Rechannelization has been proven to be a more effective term and it is the word SDOT has used since 2010.

    • That’s a good question, especially considering how powerful words can be at shaping dialog. I use the terms road diet and road rechannelization interchangeably for a few reasons. These are still commonly referred to as “road diets” outside of Seattle and even within the city. Using both terms makes the graphic more accessible to people who aren’t familiar with the rechannelization terminology. I also think it’s more readable with both terms being used. I refer to a “road diet” or “rechannelization” six times in the infographic. Using the same term every time would sound repetitive, and rechannelization is a harder word for people to read.

  • I don’t think you’ll see us printing the six-syllable word “rechannelization” anytime soon, when a concise phrase like “road diet” is available.

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