December 27, 2006

Building More Roads is One of the Worst Solutions for Congestion, Not an Answer

Sam Stanley bemoans Boston traffic gridlock, notes the soaring amount of urban vehicle miles travelled, and then trots out a tired solution that's never worked: Build more highway capacity (Making Gridlock a Priortity, today's Boston Globe op-ed page). But guess what? There's simply not enough land to keep boosting highway capacity in urban environments - not unless you want to completely destroy streetscapes, wreck neighborhoods, or spend billions of dollars per mile to build underground roadways like the Big Dig.

But even if you did that, all you'd do is escalate traffic volumes even further. "A recent University of California at Berkeley study covering thirty California counties between 1973 and 1990 found that, for every 10 percent increase in roadway capacity, traffic increased 9 percent within four years' time," note Andres Duany, Elizabeth Platter-Zyberk and Jeff Speck in the book Suburban Nation.

I agree with Stanley that we need to look at "other cost-effective ways to combat traffic," such as better traffic signal optimization and using traffic cameras to improve accident response times. Variable-priced toll lanes are also an interesting idea, making people pay premium rates to travel at premium times on congested roadways.

But keep building ever more highway capacity to encourage people to keep driving more - at a rate of increase that already far outstrips the rate of population growth? No, that's not a public policy I endorse. There's a fundamental problem question here that he's ignored: Why has there been such a huge increase in private-vehicle travel? He tosses out a statistic that urban driving miles increased more than 168% in the past 30 years, without ever questioning why that is or if there's some way to ease demand instead of stoking it. There are several reasons for this spike in passenger vehicle miles:

* Lack of affordable housing, which forces people to live ever farther away from jobs (as well as other urban attractions such as cultural sites, sporting events, commercial and retail centers, etc.)

* Patterns of development that make any other kind of travel impractical. In older town centers, people can still walk to train stations and bus stops; in urban centers, people take the subway or buses or even walk to their jobs. In some older communities, people can walk to the grocery store and kids can walk to school. In newer suburbs and exurbs, it's impossible to walk anywhere, and the McMansions went up without thought of how those people would get to jobs or shopping, simply assuming the private car for 100% of travel was viable. Build more roads without changing that kind of development, and you just have the same problem with higher traffic levels.

* People in private cars do not pay their full fair share of expenses for the roads they use. If you don't pay more for road repair, snow removal, highway construction and so on, depending on how much you drive and use those roads, then you're going to drive more - and make decisions on where to live and work that involve more driving - than you otherwise would if you had to pay the full cost per mile. If we all paid half the cost of heating oil, and tax revenues made up the difference, many of us would be cranking up our thermostats in the winter. Same with private automobile use. Fund all road construction and maintenance via the gasoline tax, and you might see some changes in private vehicle usage patterns.

* Mass transit service is deteriorating. It's bad enough that service is so sparse and infrequent that in many cases, it's not practical to use. But even when the service allegedly is there, buses and trains are late, service is painfully slow and sometimes your bus or train simply doesn't show up at all. It doesn't have to be that way. When I was in Geneva last year, every single bus, train and commuter boat I took arrived on schedule to the minute. Every one! Even buses travelling through crowded city streets at rush hour. I'd suggest some of our public officials head to Switzerland and find out how they manage this, because clearly it's possible if there's a commitment to such service.

But let me repeat the basic flaw in Stanley's argument: You'll never be able to build enough highway capacity to meet demand. Never. Spanking new uncongested highways simply encourage development patterns that rely on those highways, eventually clogging them. I remember when Rte. 495 was mostly empty, and now thanks to housing patterns which rely heavily on private vehicle travel on that highway, it's often congested. How do we fix that, then? Build another ring highway? Widen it to eight lanes each way? Where does it end?

"Building more highways and widening existing roads, almost always motivated by concern over traffic, does nothing to reduce traffic. In the long run, it actually increases traffic. This revelation is so counterintuitive that it bears repeating: adding lanes makes traffic worse," Suburban Nation points out.

"This paradox was suspected as early as 1942 by Robert Moses, who noticed that the highways he had built around New York City in 1939 were somehow generating greater traffic problems than had existed previously. Since then, the phenomenon has been well documented, most notably in 1989, when the Southern Califronia Association of Governments concluded that traffic-assistance measures, be they adding lanes, or even double-decking the roadways, would have no more than a cosmetic effect on Los Angeles' traffic problems. ...

"Across the Atlantic, the British government reached a similar conclusion. Its studies showed that increased traffic capacity causes people to drive more -- a lot more -- such that half of any driving-time savings generated by new roadways are lost in the short run. In the long run, potentially all savings are expected to be lost. In the words of the Transport Minister, 'The fact of the matter is that we cannot tackle our traffic problems by building more roads.' ...

"Increased traffic capacity makes longer commutes less burdensome, and as a result, people are willing to live farther and farther from their workplace. As increasing numbers of people make similar decisions, the long-distance commute grows as crowded as the inner city, commuters clamor for additional lanes, and the cycle repeats itself. ...

"The phenomenon of induced trafic works in reverse as well. When New York's West Side Highway collapsed in 1973, a NYDOT study showed that 93 percent of the car trips lost did not reappear elsewhere; people simply stopped driving. A similar result accompanied the destruction of San Francisco's Embarcadero Freeway in the 1989 earthquake. Citizens voted to remove the freeway entirely despite the apocalyptic warnings of traffic engineers. Surprisingly, a recent British study found that downtown road removals tend to boost local economies, while new roads lead to higher urban unemployment. ...

"The question is not how many lanes must be built to ease congestion but how many lanes of congestion you want. Do you favor four lanes of bumper-to-bumper traffic at rush hour, or sixteen? This condition is best explained by what specialists call latent demand. Since the real constraint on driving is traffic, not cost, people are always ready to make more trips when the traffic goes away. The number of latent trips is huge -- perhaps 30 percent of existing traffic. Because of latent demand, adding lanes is futile, since drivers are already poised to use them up."


  1. That's an excellent analysis. With people constantly demanding more and more highways, along with more and more parking space, one wonders when an equilibrium will be reached. Presumably, scattered somewhere within the sea of asphalt, there will still be some destinations to which people will drive.

  2. A very interesting perspective that makes perfect sense when explained. Thanks for sharing this!

    Framingham, MA

  3. Very though provoking response to the plans proposed. More locally, I live on Edgell Rd and this would greatly impact quality of life here. Many of us would leave the state. I thought the idea was to promote living in Massachusetts? Why propose paying new graduates a lump sum to stay, help those who want to stay...leave our property alone! Thank you for your analysis!