In my home state of Iowa, a discussion is moving forward on widening Interstate 380 between North Liberty and Cedar Rapids into three lanes in each direction. .
As I wrote two years ago, the impetus for widening the highway is understandable — population in Linn and Johnson counties has increased; their combined population in the 2016 census estimate is 368,208, up 7.63 percent since 2010 and 39.0 percent since 1990, both faster than the United States as a whole. Intercity commuting has increased with population — average daily traffic counts at the county line increased by about 50 percent between 1998 (38,200) and 2014 (55,600) — and drivers can at times feel trapped in traffic without an extra lane to set them free. The region and the state have sunk their investments into highway transportation, and citizens seem to approve. It seems easier to build on that than to try to create alternatives from nothing.
The arguments against the project remain as strong as they did two years ago. First, widening the highway does not merely set existing traffic free. It encourages more traffic along the highway. Increased highway capacity encourages more people to commute and existing commuters to drive more. This has been shown in numerous studies. Here are some cited by Tom Vanderbilt (Traffic: Why We Drive the Way We Do (And What It Says About Us), Knopf, 2008) and Edward Humes (Door to Door: The Magnificent, Maddening, Mysterious World of Transportation, Harper, 2016):
- A 2002 study of projects in England showed that most of the time, the increase in traffic on alternative routes was nowhere near the traffic “lost” on the affected roads (S. Cairns, S. Atkins and P. Goodwin, “Disappearing Traffic? The Story So Far,” Municipal Engineer 151:1 (March 2002), 13-22
- A 2011 project to widen a ten mile stretch of I-405 in Los Angeles from ten lanes to twelve cost $1.3 billion and resulted in (slightly) slower travel times once completed (“$1.1 Billion and Five Years Later, The 405 Congestion Relief Project Is a Fail,” Los Angeles Weekly, 4 March 2015)
- Houston’s $2.8 billion Katy Freeway project widened I-10 from eight lanes to 26 lengthened travel times (Humes 142)
- The Braess Paradox states that adding a new road to a transportation network may actually slow things down for all its users, because “user optimal” is not “system optimal” (Dietrich Braess, “On a Paradox of Traffic Planning,” Transportation Science 39 (2005): 446-450
- Based on experience of London (and before that, Disneyland), Tom Vanderbilt recommends congestion pricing as the solution to traffic congestion (Vanderbilt 2008: 175)… though it’s not clear to me what congestion means in an Iowa context
More driving is, pure and simple, bad for the environment, which is, let us recall, what we are all living in, breathing and drinking. Not only does auto exhaust pollute the air (Stone 2008), the carbon emissions contribute to climate change (Bereitschaft and Debbage 2013), which is far enough along that it ought at least to bother people. Though Eastern Iowa is not Houston, sprawl also has a negative effect on animals and plants (cf. Weller 2018).
Furthermore, in the current fiscal environment, the costs of widening the highway alone are unconscionable — without even bringing opportunity costs to bear. The American Road and Transportation Builders Association estimates the cost to widen a highway from four lanes to six at $4 million per mile, which would make the total project cost $40 million. Even if this were on the nose, which I'm doubting, this is a transfer of funds from non-commuters to commuters. Even if the money were there, is this really the best use of it? The State of Iowa has been cutting mental health spending, and is increasing K-12 education below inflation, choices forced by its fiscal crisis. The national government, which for the time being remains a substantial source of state highway funds, just passed $500 million in spending on top of a $1.5 billion tax cut, which will aggravate its own fiscal crisis. We've heard repeatedly for the last three decades that our nation’s infrastructure is crumbling. So why is our response to build more?
After the highway is built and development follows, it falls to city and county governments to follow up with streets, pipes, and year-to-year maintenance. It falls to school districts to get these farther-flung children to school. None of these governments are flush, either. It hardly behooves them to spread their responsibilities farther.
Finally, while the idea that more highway capacity will relieve congestion and improve safety has intuitive appeal, in practice, these hopes are generally blasted. Besides the induced demand studies cited above, there is evidence that wider roads do not improve safety, either because more open lanes encourage higher driving speeds or because induced demand eventually restores the former level of traffic density.
“If you build a road that’s wide, has a lot of sight distance, has a large median, large shoulders, and the driver feels safe, they’re going to go fast,” says Tom Granda, a psychologist employed by the Federal Highway Administration (FHWA). “It doesn’t matter what speed or sign you have. In fact, the engineers who built that road seduced the driver to go that fast” (Vanderbilt 2008: 183).
My guess is that safety on a six-lane highway would either be a push or a slight decline. (Stroads present many more safety issues than even high-speed highways.) Interstate highways are engineered for speed and safety. I would caution that more open road means higher speeds, and that more lanes means more jockeying, at least in rush hour.
One more note: In the medium-term, should further capacity be needed, it’s much easier to scale up public transit by adding more bus and train runs than it is to build still more highway lanes.