Skip to Content
Streetsblog USA home
Streetsblog USA home
Log In
State DOTs

Transpo Agencies Are Terrible at Predicting Traffic Levels

This chart contrasts state DOTs' projected traffic volumes with those actually recorded by the Federal Highway Administration. Image: ##http://www.ssti.us/2013/12/new-travel-demand-projections-are-due-from-u-s-dot-will-they-be-accurate-this-time/?utm_source=SSTI+Community+of+Practice+Master+List&utm_campaign=cbd2d0b53a-December_6_2013_newsletter12_16_2013&utm_medium=email&utm_term=0_f54dd1d9a6-cbd2d0b53a-45447449## SSTI##
Combined traffic projections from state and regional transportation agencies (the colored lines) have been wildly off the mark (the black line shows real traffic levels) for more than a decade. Image: ##http://www.ssti.us/2013/12/new-travel-demand-projections-are-due-from-u-s-dot-will-they-be-accurate-this-time/?utm_source=SSTI+Community+of+Practice+Master+List&utm_campaign=cbd2d0b53a-December_6_2013_newsletter12_16_2013&utm_medium=email&utm_term=0_f54dd1d9a6-cbd2d0b53a-45447449##SSTI##
This chart contrasts state DOTs' projected traffic volumes with those actually recorded by the Federal Highway Administration. Image: ##http://www.ssti.us/2013/12/new-travel-demand-projections-are-due-from-u-s-dot-will-they-be-accurate-this-time/?utm_source=SSTI+Community+of+Practice+Master+List&utm_campaign=cbd2d0b53a-December_6_2013_newsletter12_16_2013&utm_medium=email&utm_term=0_f54dd1d9a6-cbd2d0b53a-45447449## SSTI##

Americans' travel behavior is changing dramatically. It seems like not a week passes without a new report about the decline in driving. But are state and local transportation agencies -- which are responsible for much of the nation's highway and transportation planning -- keeping up with the facts on the ground? A review of the evidence by the State Smart Transportation Initiative finds the answer is a definitive "No."

Forecasts and assumptions about ever-increasing traffic are often used to justify agency decisions to expand roads. But these assumptions are increasingly divorced from reality. In fact, state and regional agencies aren't just wrong some of the time. State DOTs and metropolitan planning organizations are getting it wrong every year, over and over again, by significant margins, according to SSTI's analysis.

In their most recent reporting to the Federal Highway Administration, state and regional transportation agencies used data from 2008 to predict that traffic volumes would reach a combined 3.3 trillion miles nationally in 2012. Last year, a few months after that forecast was publicly released, real-world data already showed that the forecast wasn't even close. Transportation agencies had collectively overestimated how many miles Americans would drive in 2012 by 11 percent. That is the equivalent of adding five "average-sized" states to the total, SSTI reports.

What's worse, these wildly incorrect traffic assumptions are routinely used to justify costly road expansions.

SSTI reviewed every 20-year traffic forecast submitted by state and regional agencies to FHWA since 1999 (these predictions are in a document called the Conditions and Performance Report to Congress). It turns out that the 20-year projections overestimated future traffic volumes in every single year the reports could be compared against data on actual miles driven by Americans. The 1999 report, for example, overestimated actual driving in 2012 by a whopping 22 percent.

SSTI's Eric Sundquist concluded that states and MPOs "generally have not updated their models and assumptions to account for current conditions, as if they expect the year to be 1980 forever."

Stay in touch

Sign up for our free newsletter

More from Streetsblog USA

Wednesday’s Headlines Have a System

The safe systems approach to street design, popular in Europe, could cut U.S. traffic deaths in half.

May 21, 2025

Does Transportation Advocacy Have a Place In the Wake of a Deadly Tornado?

Much of St. Louis is struggling in the wake of a deadly tornado. Amid such disasters, urbanism needs a pause and a rethink.

May 21, 2025

Tuesday’s Headlines Show Elections Have Consequences

"Woke" transit agencies need not apply for federal grants now that father of nine Sean Duffy is in charge.

May 20, 2025

Should We Treat the Local Bus As a Basic Right?

There's a way of framing public transit that makes the bus a useful mobility tool for everyone: as a moving extension of the sidewalk network.

May 20, 2025

Op-Ed: Public Transportation is Key to Social Mobility

"As wealth inequality grows and social mobility becomes more difficult, people without access to mobility will be left behind."

May 19, 2025

Car Harms Monday: Machines Took Over Cities and Left Humans in the Dust

There isn't enough physical space for every single household to store its fleet of personal vehicles in front of the home, nor is there space for everyone to drive at the same time. So let's fix that.

May 19, 2025
See all posts