Widening Roads Leads to More Greenhouse Gas Emissions

Building new additional highway lanes increases total global warming emissions over the long term — even if the project reduces congestion and emissions over the short term. Sightline’s analysis of highway-widening projects and road emissions has implications for transportation proposals such as the Columbia River Crossing between Oregon and Washington, and the Gateway Project in greater Vancouver, BC.
Increases in greenhouse-gas emissions from highway-widening projects
Sightline’s blog post explaining the analysis: Does Congestion Relief Equal Climate Relief?

Brief summary

  • Adding lanes to a highway will increase total global warming emissions over the long term — even if it reduces congestion over the short term.
  • Specifically — we estimate that each extra lane-mile built will increase emissions of carbon-dioxide, the main greenhouse gas, by more than 100,000 tons over 50 years.
  • Any short-term fuel savings from congestion relief are quickly overwhelmed by increased traffic volumes on the roadway.
  • This estimate takes into account the potential for major increases in vehicle fuel efficiency over 50 years. Even assuming major mpg improvements, we still find that total road emissions rise when congested highways are widened.
  • However, if our region adopts a comprehensive, economy-wide cap on global warming emissions, concerns about the global-warming impacts of highway widening would be reduced.

More information: Sightline’s climate policy project

Published: October 7, 2007