Calculating the carbon cost of more lanes of freeway

Environmentalists like those of the Sierra Club aren't happy about the pavement portion of Proposition 1, the $17 billion roads-and-transit measure on the November ballot. So in terms of the carbon footprint, how bad is it?
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Environmentalists like those of the Sierra Club aren't happy about the pavement portion of Proposition 1, the $17 billion roads-and-transit measure on the November ballot. So in terms of the carbon footprint, how bad is it?

Over the past week or so, there's been a big to-do about greater Seattle's transportation measure, Proposition 1, which will appear on the November ballot in King, Pierce, and Snohomish counties. The measure would spend more than $17 billion on new roads, road maintenance, and rail transit, mostly through an increase in sales and vehicle taxes.

To many people's surprise, King County Executive Ron Sims, a former board chair of Sound Transit, came out against Proposition 1 last week in an op-ed published in The Seattle Times. A chief reason for his opposition: global warming. Said Sims:

Tragically, this plan continues the national policy of ignoring our impacts upon global warming. In a region known for our leadership efforts to reduce greenhouse gases, this plan will actually boost harmful carbon emissions.

On this latter claim, I think that Executive Sims could well be correct.

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 – which you can read in full [88K PDF] – 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

For a variety of reasons, which the full memo discusses in greater depth, these are conservative estimates. And to put all this in context: CO2 emissions in the U.S. currently average about 20 tons per person per year. So 100,000 tons per lane-mile is a fair bit of CO2 – not as much as a coal-fired power plant, but worth being concerned about. As I understand the package, Proposition 1 would add over 150 lane-miles of general purpose roadways – which, over the long term, could increase CO2 emissions by some 15 million tons.

Obviously, this isn't a full analysis of Proposition 1. It doesn't look at the greenhouse gas impacts of building or operating a train or HOV/HOT lanes, nor of the land-use impacts of more compact development that light rail might help foster. Still, Executive Sims may be on to something; if our estimates are even close to the mark, the greenhouse-gas impact of building new roads is pretty substantial.

The relationship between road building and CO2 emissions has relevance far beyond this year's Proposition 1 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.

To me, 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. Sure, congestion relief might help in the short term – say, five to 10 years. (Even then, it's pretty slim stuff.) But over the long term, traffic in crowded urban areas tends to fill all available road space. And when roads fill up, we'll just have an extra highway lane filled with idling traffic – and the extra emissions from new traffic positively dwarf any temporary decline in emissions from congestion relief.

Sightline isn't taking a position on Proposition 1 as a whole. There are a lot of complicated tradeoffs that we just haven't looked at – and which, frankly, we don't have time to examine. [Editor's note: Crosscut contributor Emory Bundy has taken a run at calculating the carbon footprint of light rail.]

For example, the Proposition 1 financing scheme, relying heavily on a sales-tax increase, falls most heavily on working families. And that would make our tax system – already the most regressive in the US [76K PDF] – even less fair. But building roads and trains can create high-wage jobs for people who don't have college degrees. The overall economic equity impacts are hard to gauge without an in-depth look at the regional economy.

Just so, the long-term impact on land use is hard to judge. Building light rail could foster compact land use, and folks in compact neighborhoods tend to drive less. But this will depend in large measure on what happens to the land surrounding each rail stop: Will it be up-zoned and surrounded by complete, compact communities? Or will it become parking lots and kiss-and-ride stations surrounded by sprawl-as-usual? Plus, even if trains do foster compact, pedestrian-friendly neighborhoods, will that offset the car-dependent development made possible by the new highway capacity? (After all, Proposition 1 adds more than twice as many lane-miles of roads than of transit.)

And finally, if the state of Washington (or the U.S. as a whole) does adopt a comprehensive, aggressive greenhouse gas cap, the issue of CO2 from road building is more or less moot. A cap would force overall carbon emissions down, regardless of how many new lanes of highway are built. Sure, highway building could make greenhouse compliance more expensive. But it won't put it out of reach. That said: Who knows how the politics of global warming will play out? We could wind up with no cap, or a phony cap that excludes transportation fuels. If so, extra roads could become a real problem.

Sure, I have some hunches about how these sorts of issues would play out. But hunches shouldn't substitute for facts. Before Sightline took a position on Proposition 1, we'd want good, reasoned answers to many of these questions – answers that we, regrettably, don't have time for.

Still, one thing is clear: Building highways for the sake of "congestion relief" will increase CO2 emissions from highways. And now we have some numbers to back this up.


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