Skip to Content
Streetsblog New York City home
Streetsblog New York City home
Log In
Around the Block

The Science Is Clear: More Highways Equals More Traffic. Why Are DOTs Still Ignoring It?

Numerous studies have documented the phenomenon known as induced demand in transportation: Basically, if you build highway lanes, more drivers will come. And yet, transportation agencies rarely account for this effect when planning road projects.

In a recent paper published by the Transportation Research Record, author Ronald Milam and his research team reviewed the various studies documenting the induced demand effect. They found that for every 1 percent increase in highway capacity, traffic increases 0.29 to 1.1 percent in the long term (about five years out), and up to 0.68 percent in the short term (one or two years). One recent study found a one-to-one relationship between new highway lane capacity and traffic increases.

However, highway planners are failing to incorporate this effect into their models. Milam told Streetsblog that "it is rare to find an induced travel analysis in most transportation infrastructure design or environmental impact analysis." That means transportation agencies are green-lighting money for highway expansions that are destined to become congested again only short time later.

While some transportation agencies may lack the sophistication to model induced demand accurately, they should not disregard the phenomenon, Milam and his team write.

Highway planners should assume traffic increases will result from highway expansion projects in line with what previous research has demonstrated, the authors conclude.

More recommended reading today: nextSTL publishes a poem about the epic struggle to convince the Missouri Department of Transportation to design a walkable Gravios street. ATL Urbanist reports MARTA will take over operations of the struggling Atlanta Streetcar. And Streets.mn looks at the relative dearth of retail stores in urban locations in the Twin Cities.

Stay in touch

Sign up for our free newsletter

More from Streetsblog New York City

Trump Culture War Tantrum Turns to Gateway Tunnel and Second Ave. Subway

It's the second time the Trump administration has denied New York transit funding in as many days.

October 1, 2025

West Side Pols Call on Trump Administration to Stop Illegally Blocking 10th Ave. Bike Lane

The DEA blockade of the 10th Avenue bike lane continues, and local politicians are demanding the federal agency stop denying cyclists safety.

October 1, 2025

When the DOT Takes Your Bike: A Cyclist’s Guide to Getting It Back 

A bike commuter's frustrating journey through New York's bureaucratic maze reveals a hidden problem affecting cyclists citywide. 

October 1, 2025

Wednesday’s Headlines: This is Your DOT on Drugs Edition

Yes, that's our editor consuming drugs in front of the federal Drug Enforcement Administration office on 10th Avenue to protest the agency's seizure of the bike lane. Plus other news.

October 1, 2025

BIG ZERO: Trump Stiffs MTA in ‘Sanctuary City’ Tantrum

The federal government is denying the MTA tens of millions of dollars in public safety funding over of New York's immigration policies.

September 30, 2025

Gale’s A-Blowin’: Brewer Abandons Daylighting Bill After Push By Parking-First DOT

DOT's anti-daylighting "scare tactics" have peeled off Council Member Gale Brewer, who says the policy will gobble up too many parking spots.

September 30, 2025
See all posts