Skip to Content
Streetsblog USA home
Streetsblog USA home
Log In
Portland

Transit Can Cut Car Traffic Much More Than Ridership Alone Suggests

Portland's Max Blue Line Light Rail helped reduce driving far more than its ridership numbers would suggest, a new study finds. Photo: TriNet
Portland's MAX Blue light rail line helped reduce driving far more than you would expect based on ridership alone. Photo: TriMet
Portland's Max Blue Line Light Rail helped reduce driving far more than its ridership numbers would suggest, a new study finds. Photo: TriNet

How much traffic does a transit line keep off the streets? Looking at ridership alone only tells part of the story, according a new study published in the Journal of the American Planning Association. The full impact of a transit line on motor vehicle traffic can far exceed the direct effect of substituting rail or bus trips for car trips.

Using data from the Portland region, University of Utah researchers Reid Ewing and Shima Hamidi compared self-reported travel in an area where a light rail line was built to an area that saw no transit investment.

The team collected data on changes in travel behavior in the area served by the MAX Blue light rail line and in the area around SW Pacific Highway. They compared stats from 1994 -- before light rail was built -- and 2011 -- 13 years after it launched. They opted to use the 2011 data in order to show the full impact of denser, transit-oriented development around the stations.

Ewing and Hamidi found that light rail led to an average of 0.6 additional transit trips per day among each household in the surrounding community. By itself that would have cut total driving mileage by about a half mile per household per day -- not a huge impact.

But the effect on driving among households living near light rail was much greater than that.

From 1994 to 2011, households in the area without new transit increased their driving by 62 percent (from 18.25 miles per day to 29.4), while households living near the new light rail line increased their driving only 22 percent (from 17.4 miles to 21.2).

Why was this effect so much larger than the effect directly attributable to new transit trips? Partly because households living near the light rail walked more and traveled shorter distances when they did drive. Walking increased 151 percent among people living in the transit-oriented communities, Ewing and Hamidi found.

That was possible because, following the addition of light rail, city, regional, and state agencies took steps to encourage walkable development around the transit line. And it worked. According to Ewing and Hamidi the "activity density" of the light-rail neighborhoods -- a measure of how many households and jobs are located in a given area -- rose 100 percent between 1994 and 2011.

The total driving mileage avoided by households living near transit amounted to three times the avoided mileage due solely to switching from driving to transit. Similar studies have estimated this "multiplier effect" to be in the range between 1.9 and 9.

Stay in touch

Sign up for our free newsletter

More from Streetsblog USA

Friday Video: The London Neighborhood Where Bikes Outnumber Cars

...and how they got to that impressive milestone.

July 11, 2025

Friday’s Headlines Battle Galactus

Like the Marvel supervillain, U.S. interstate highway system seems to eat up everything in his path. A new book explores how to stop it.

July 11, 2025

New Report Shows Pedestrian Fatalities Drop — But Experts Say Not Enough

The Governors Highway Safety Association report showed a 4 percent drop in the number of pedestrian deaths last year, putting a slow on a dangerous trend — but advocates say the drop isn't nearly big enough.

July 11, 2025

Talking Headways Podcast: Localities Subsidize the State DOT

Adie Tomer of Brookings on how to improve regional coordination around infrastructure.

July 10, 2025

Five of the Ugliest Transportation Policies In the ‘Big, Beautiful’ Bill

Here's a rundown of some of the transportation provisions in the Republicans' reconciliation package, and what they might mean for your community.

July 10, 2025

Viva La Thursday’s Headlines

Why is French transit ridership up 10 percent since before the pandemic, while American transit ridership is down 23 percent?

July 10, 2025
See all posts