More Lanes Mean More Emissions

As Seattle considers a plan to spend more than $17 billion on road and transit projects, the Sightline Institute looks at how the city's greenhouse-gas emissions would increase if a new land of highway is built.

1 minute read

October 8, 2007, 10:00 AM PDT

By Nate Berg


"We recently took a look at the greenhouse gas implications of building a new lane-mile of highway in a congested urban area. Our conclusion is that every extra one-mile stretch of lane added to a congested highway will increase climate-warming CO2 emissions more than 100,000 tons over 50 years. Those emissions are broken out as follows:

* Road construction and maintenance: 3,500 tons

* Net congestion relief: -7,000 tons [that's negative, folks]

* Additional traffic on the roadway: 90,000 tons

* Additional traffic off the roadway: 30,000 - 100,000 tons

* TOTAL: 116,500 - 186,500 tons

The relationship between road building and CO2 emissions has relevance far beyond this year's RTID debate. British Columbia is considering a massive roadway expansion in greater Vancouver, called the Gateway Program, which includes a controversial twinning of the Port Mann Bridge. And major road widening proposals occasionally rear their heads throughout Cascadia and beyond."

"The most curious thing is that some supporters of this sort of road expansion try to claim the environmental high-ground: adding lanes to crowded highways, they claim, will relieve congestion, which will reduce overall emissions."

"Our analysis shows this claim is bunk."

Thursday, October 4, 2007 in Sightline Institute

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Cover CM Credits, Earn Certificates, Push Your Career Forward

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

June 18, 2025 - Diana Ionescu

Rendering of Shirley Chisholm Village four-story housing development with person biking in front.

San Francisco's School District Spent $105M To Build Affordable Housing for Teachers — And That's Just the Beginning

SFUSD joins a growing list of school districts using their land holdings to address housing affordability challenges faced by their own employees.

June 8, 2025 - Fast Company

Two people walking away from camera through pedestrian plaza in street in Richmond, Virginia with purple and white city bus moving in background.

Vehicle-related Deaths Drop 29% in Richmond, VA

The seventh year of the city's Vision Zero strategy also cut the number of people killed in alcohol-related crashes by half.

June 17, 2025 - WRIC

Rendering of proposed 38-story tower in downtown Portland, Maine.

Downtown Portland Ready for Maine's Tallest Building

The city of Portland anticipates a major new urban development addition called the “Old Port Square” project.  

15 minutes ago - News Center Maine

Map of EV charging ports in rural U.S. communities.

The EV “Charging Divide” Plaguing Rural America

With “the deck stacked” against rural areas, will the great electric American road trip ever be a reality?

June 20 - The Daily Yonder

Google street view of Bedford Avenue in Brooklyn with pedestrians crossing a crosswalk and cyclist in the bike lane.

Judge Halts Brooklyn Bike Lane Removal

Lawyers must prove the city was not acting “arbitrarily, capriciously, and illegally” in ordering the hasty removal.

June 20 - StreetsBlog NYC