The Livable Blog

A new report from the Sightline Institute calculates GHG emission increases due to widening of a highway.

Road-building proponents often suggest that adding lanes to a highway will reduce greenhouse gas emissions. By easing congestion, they argue, new lanes will reduce the amount of fuel that vehicles waste in stop-and-go traffic, leading to lower releases of climate-warming gases from cars and trucks.

Over the short term---perhaps 5 to 10 years after new lanes are opened to traffic---this argument may hold some slim merit. But considering the increased emissions from highway construction and additional vehicle travel, adding one mile of new highway lane will increase CO2 emissions by more than 100,000 tons over 50 years.

I encourage you to read this report, It is short and easy for non-experts (like me) to understand. Cutting to the chase, here are their conclusions:

Carbon dioxide emissions from building one lane-mile of urban highway, over 50 years

What is interesting about this report is that the method used is simple and sound even if the report makes generalizations and speculations about costs and future technology. These are educated speculations but could nonetheless be wildly off, on either end. For example, the report conservatively (i.e., understating their argument, given current trends) posits that cars will emit 1/3 as much GHG per mile in 50 years as they do now. We can quibble about how far off their numbers will be, but it is unlikely to change their thesis, that highway construction creates more GHG emissions.

To be fair, we should additionally be looking at the emissions from adding a world-class transit system in lieu of an expanded highway. Heavy rail and light rail produce emissions during construction, operation, and maintenance. Based on this presentation, produced by Institute for Sustainability and Technology Policy at Murdoch University in Australia, as we would expect, public transit produces much lower. However, I am looking forward to a Sightline report on this issue.