Why aren't America's national roadways working?

What are some of the core arguments of your book, and how do these issues affect our daily lives?

One is that the U.S. has too many and too high-capacity highways and arterials. Second, we continue to build and widen highways and arterials despite the results being contrary to our stated public policies around safety, the environment, and economic competitiveness since around the 1990s. And third, the financing and evaluation methods that justified highway building in the mid-20th century remain in place, so we keep reproducing the same mistakes.

This overbuilding leaves Americans way more car-dependent than they might prefer. I think most of us would like the option to walk safely to the store without getting run over, spend less on gas and insurance, and live in less polluted environments, but we’ve poured so much into roads that we’re past the point of diminishing returns—new widenings often make us worse off when you account for collisions, emissions, and fatalities.

How does the U.S. pay for more highways?

Primarily through a flat federal gas tax. That means whether you’re driving on a quiet residential street or in downtown congestion, you pay the same per gallon. The revenues are then disproportionately used on the most expensive projects, like widening urban highways, where you’d have to buy up really expensive urban real estate—potentially tearing down houses causing more pollution and more congestion.

You could think of it this way: Imagine we taxed every acre of farmland the same amount and used that revenue to subsidize the most expensive use—let’s just say grass-fed beef. More and more land would get used for beef production and less for corn, chicken, and other agricultural products. This would not only be restrictive for people who choose to or are unable to consume beef, but it would also be environmentally unsustainable.

In terms of transportation policy, we’re essentially lowering the cost of the most expensive, most congested trips, which just encourages people to take more of them.

Does having an expansive highway network make travel safer in the U.S.?

Not really. Although improving traffic safety has remained a top priority, the U.S. traffic fatality rate is three to four times higher than most peer countries—around 12 to 13 deaths per 100,000 people. Highways themselves are relatively safe, but the arterials and feeder roads—where speed and design make them dangerous—are where most fatalities occur.

I think you can actually sum it up in a pretty simple way, and that’s Americans drive a lot more; they also drive greater distances. And they drive a lot more with a much higher risk rate. So, the probability of dying per person is really high.

Widening roads is the go-to solution when congestion mounts. Why doesn’t that work?

Because transportation runs on supply and demand. When you increase capacity, you lower the cost of using it, and demand rises to fill the road. Research shows almost a one-to-one relationship between widening highways and increasing traffic—what’s known as the ‘fundamental law of road congestion.’ Yet projects are still approved with unreliable traffic projections. Agencies will assume, say, 3% annual traffic growth—doubling every 20 years—and then calculate enormous ‘time savings’ if a road is widened. It’s a flawed process that produces absurd benefit estimates.

If not public transportation and not widening, what’s the alternative?

Erick Guerra is Professor of Regional Planning and Associate Dean for Research at the Weitzman School.

(Image: Courtesy of Erick Guerra)

I get why people—especially people outside of transportation planning—assume the solution to highway traffic is just to build more buses and trains. But I don’t see much evidence suggesting that big investments in public transit reduce traffic congestion. Even in Philadelphia, our region’s transit doesn’t work well for most suburb-to-suburb trips.

I believe the path forward isn’t immediately through transit, but through fundamentally changing highway policy: We need to make highway expansion and widening a policy of last resort, instead of the automatic default public policy it is now. We also need to fix how we pay for roads, moving away from a flat gas tax (which disproportionately funds expensive urban highways) toward charging prices that better reflect the marginal cost of the actual trip—driving on a rural residential street shouldn’t equate to a congested downtown one. Ultimately, most Americans are going to be driving, no matter what.

If we had never spent decades prioritizing and subsidizing driving through massive urban highway investment, people would still use their cars, but they would likely drive shorter distances, and our cities wouldn't be so auto-dominated. This change in urban form would actually make alternative transportation modes, like walking to the corner store, much more feasible for daily activities. If we implement these core reforms, maybe 20 or 30 years down the line, more places might become ‘amendable to transit.’

Can self-driving cars save the day?

Automated vehicles are often pitched as a technoutopia. Some estimates suggest they could increase highway capacity fivefold. If that’s true, why spend billions widening highways today?

But history shows that technological fixes rarely deliver as promised. Simulations, for example, already suggest potential dystopias—robotaxis cruising endlessly through downtown streets rather than paying for parking. And while they might reduce certain crashes, the idea they’ll solve congestion or safety entirely is wishful thinking.

What’s the right amount of highway?

Highways play an invaluable role in modern society, so there’s no way without them. But at the same time, Philadelphia lost entire blocks to mid-century highways. Reclaiming some of that space for housing, shops, or parks could make cities safer, more vibrant, and less car-dominated. The goal is to strike a balance between negative space—roads that define the shape and form of cities and towns—and positive space for people.

Philadelphia sits in the aging Northeast Corridor. What opportunities does a city like this have?

Eventually, every piece of infrastructure gets rebuilt. That’s an opportunity. Instead of simply replacing or widening highways, older cities can rethink them: downgrade, remove, bury, or cap them to reconnect neighborhoods.