Skip to Content
Streetsblog New York City home
Streetsblog New York City home
Log In
Development

How Better Traffic Models Can Lead to More Mixed-Use Development

Here's another obscure but significant obstacle to building walkable places in America: the Institute of Transportation Engineers' shoddy traffic generation models for mixed-use development.

The model used by traffic engineers around the country to measure "trip generation" at new developments consistently overestimates the amount of motor vehicle traffic produced by mixed-use projects, according to the Environmental Protection Agency. This often increases the cost of building mixed-use projects, because the developers are asked to take steps to compensate for the added traffic. To address this problem, the EPA worked with transportation researchers around the United States to develop a better traffic prediction model.

false

Reid Ewing, a transportation engineering professor at the University of Utah, helped develop the new model to forecast the traffic generation of walkable development. I caught up with him at the Congress for New Urbanism conference last week in Salt Lake City.

Angie Schmitt: Can you explain the new method?

Reid Ewing: There’s a current methodology, which is the Institute of Transportation Engineers’, and it overestimates the number of external vehicle trips generated by a development if the development has mixed uses. If it’s got residential, retail, and office, those uses interact and a lot of trips stay within the development. And if it’s a development downtown, a lot of those trips that leave the development are walk and transit trips. ITE doesn’t account for that, it doesn’t account for the full number of trips that will stay within a development or the use of alternative modes for those that leave the development. So we developed a methodology.

AS: How many trips are reduced by mixed-use development?

RE: It varies from almost zero to over 50 percent. In a master planned community, it’s huge -- a lot of the trips are going to stay within the community. If you have a stand-alone, freeway-oriented community that happens to have mixed-used, a much smaller percentage will stay within the community. But on average, about 35 percent. So the ITE method seems to overestimate by, on average, about 35 percent.

AS: So, how does the ITE method cause problems?

RE: If the developer proposes a mixed-use development, it doesn’t get credit for trip reduction. So that means the developer will pay more in impact fees and would be required to do more offsite improvements, that are required by the development to mitigate its impact. More parking is required to be provided than a mixed-use development really needs. The roads are scaled and sized according to numbers that inflate the actual capacity needs of the road. So there are all sorts of direct and indirect impacts.

So our effort, our original effort, was funded by the Environmental Protection Agency. They were doing it as a way of promoting smart growth. They wanted to do what they could to promote smart growth, and one of the ways was to offer an alternative to [the method used by] ITE.

AS: How many places have adopted the new model?

RE: I have no idea. I know that the state of Virginia has adopted it. The Utah Transit authority has. The Wasatch Front Regional Council of Governments [Salt Lake City's metropolitan planning organization] has also.

Until the methodology finds its way into the ITE trip generation handbook, it still won’t be widely used.

Stay in touch

Sign up for our free newsletter

More from Streetsblog New York City

Ugly Truth: Feds’ Canal Street Raid Pushed Aside NYPD, Safety and Free Speech

President Trump's heavily armed and masked immigration troops are turning American cities into battlegrounds — and eliminating accountability and free speech in the public realm.

October 27, 2025

Bikelashers Beware! Court Street Redesign Has Turned Chaos to Safety

Court Street's protected bike lane already shows a lot of promise. But that doesn't stop the hate.

October 27, 2025

Adams Administration Has Made It Nearly Impossible To Build Safe E-Bike Charging Stations

It's impossible to build an e-bike charging cabinet in NYC, despite city initiatives meant to boost the industry.

October 27, 2025

That’s Rich! DoorDash Supports E-Bike Speed Limit

DoorDash supports a 15-mile-per-hour speed limit, but that's easy for them to say, given that under-pressure workers will be the ones getting tickets.

October 27, 2025

Monday’s Headlines: Everybody to the Limit Edition

Mayoral frontrunner Zohran Mamdani wants to keep the 15-mph Citi Bike e-bike speed limit. Plus more news.

October 27, 2025

Friday Video: Amtrak Is Way More Successful Than You Think

Why do so many people still treat Amtrak as a failure — and what would it take to deliver the rail investment that American riders deserve?

October 24, 2025
See all posts