Interstate 95 and Induced Demand

Kudos to the Pennsylvania Department of Transportation for constructing a temporary replacement for a collapsed overpass in just 12 days, something that many predicted would take months. The replacement is just six lanes wide rather than the eight on the original overpass, but that leaves room for the department to construct a permanent replacement.

Some people are drawing the wrong lessons from the response to the highway collapse, however. According to Joe Cortright, the fact that there was no “carmageddon” during the 12 days the highway was closed proves that we don’t need highways at all. According to what Cortright calls the “science of ‘induced demand,'” building new roads simply leads to more driving and, conversely, closing roads leads to “traffic evaporation.”

Cortright clearly has no empathy for automobile users as he imagines that a lot of driving is really unnecessary and that alternative forms of travel (or not traveling at all) are just as good. Yes, people responded to the closed freeway by changing their travel patterns, but that doesn’t mean those changes were cost-free.

To start with, I-95 is a heavily used freight corridor. According to the Bureau of Transportation Statistics, more than 46 percent of all ton-miles of freight shipped in this country goes by truck. While I think that’s a little high, the real number is still somewhere around 40 percent and more than 40 percent of that heavy truck traffic is on interstate freeways. Take away the interstates and deliveries take longer and become more expensive.

The typical Philadelphia resident can reach more jobs in a 20-minute auto drive than a 60-minute transit trip, making transit an inefficient form of travel. Source: University of Minnesota Accessibility Observatory.

Then there’s passenger travel. I suspect that Cortright, like the Antiplanner, works at home, so he may not be acutely aware that a lot of people, especially working-class people, still commute to work by automobile. According to the 2021 American Community Survey, nearly 24 percent of Philadelphia-area income earners are working at home, but of the remainder, 87 percent rely on automobiles to get to work while less than 7 percent take transit for the good reason that, even in Philadelphia, which has rapid transit, streetcars, and commuter trains, people can reach far more jobs by car than by transit. Not all of the auto users drove on I-95, but many did and for many alternative routes must have been time-consuming. Low-income (<$25,000) workers in the Philadelphia area are less likely to work at home and more likely to rely on automobiles to get to work than high-income (>$50,000) workers, so low-income people are more severely affected by road closures.

The whole so-called science of induced demand is a joke anyway. Merely building roads doesn’t induce travel any more than simply manufacturing a product guarantees that it will sell. If conditions are right and the highway is built in the right place, it will generate new economic activity — jobs, housing, factories, retailing — which can significantly boost the economy. People like Cortright can’t argue against new economic activity so they imply that driving is frivolous.

Americans are better off having highways to drive on because they give us access to higher-paying jobs, better housing, lower-cost consumer goods, and many other benefits. Cortright’s goals would reduce those benefits and the impacts of those reductions would fall mainly on lower-income people whose jobs don’t allow them to work at home or work on flex-time schedules.