A premise at the heart of much current and proposed highway policy is that because motor vehicles are carbon polluters, an increase in vehicle miles of travel (VMT) is bad. Hence, even if aging highways are rebuilt, they should not have their capacity increased. This idea is ascendant in Europe, it’s already policy in California, and it seems to be a theme of the Biden administration’s infrastructure proposal.
Transportation Secretary Pete Buttigieg recently said that although we do need to fix “the roads and bridges that we already have,” our transportation policies also “must adapt to the reality of climate change” and “build-out high-speed and other passenger rail” to “reduce car dependence.”
In proposing a new agenda for the U.S. Department of Transportation (USDOT) last year, the center-left think tank Center for American Progress argued that federal law should be changed to require states to “model the estimated GHG (greenhouse gas) emissions from new highway capacity over a 30-year period and then develop a plan to fully offset those emissions.”
Far more radical was last year’s scathing attack on the Transportation Research Board’s (TRB) massive report on the needed reconstruction and selective widening of the Interstate Highway System. City Observatory’s Joe Cortright, for example, labeled the TRB expert committee’s report as the “highway to hell,” claiming that “policies that discourage driving will be essential to saving the planet.”
This assessment of future highways is entirely static. It ignores major changes underway in surface transportation. Even a very ambitious plan to rebuild (and selectively widen) the large majority of our Interstates—using toll finance and public-private partnership (P3) procurement—would take at least 30 years before most of those corridors were modernized and open to traffic. That’s 2050 or later.
The question not being asked is what else will change between now and 2050?
For one thing, the majority of personal motor vehicles will likely be electric by then. We have passed peak gasoline use and since electric vehicles don’t pay gas taxes we will have to start fairly soon replacing per-gallon fuel taxes with per-mile charges. Many of the remaining internal combustion engines get much higher miles per gallon and produce far fewer emissions than they used to, while the growing majority of electric vehicles (EV) will emit none.
This goal is a key policy objective of the Biden administration, and at least portions of it (such as a national network of EV charging stations) already have bipartisan support. All but one or two major auto companies have committed to cease producing petroleum-fueled vehicles by 2030 or 2035, and the federal government and many state governments are likely to continue subsidizing EV purchases.
Something similar is happening in trucking. Every major European, Japanese, and U.S. truck manufacturer is developing electric trucks, whether battery-electric or hydrogen-fuel-cell-electric. And while so far only California has announced future limitations on the sale of petroleum-fueled trucks, that idea could well get included in a federal infrastructure bill and/or be copied by other states. Initial take-up by trucking companies may be slow, but once it becomes clear that range problems have been solved and that electric trucks have lower life-cycle cost, the transition may occur faster than for passenger vehicles, because truck fleet turnover is about twice as fast for trucking as for passenger vehicles.
And then there is the advent of autonomous vehicles (AVs). My Reason colleagues who frequent AV conferences report a growing consensus among experts that the widespread availability of level 4 automated vehicles (fully self-driving on major roads in all weather conditions) will lead to greater vehicle miles traveled than status-quo VMT projections. A noted example is a 2020 paper by University of Texas—Austin engineering researcher Kara Kockelman and colleagues, “Anticipating Long-Distance Travel Shifts Due to Self-Driving Vehicles.”
They adapted a much-used model of inter-regional travel and projected a significant shift from short/medium-haul air travel to AVs. They also found that personal auto trips would be longer-distance than trips people take in conventional vehicles. While no one has a solid prediction of when level 4 AVs will be on the market and in wide use, many think this will be happening in 2030 and will be widespread in the 2040-2050 time frame.
Putting all this together, with truck VMT expected to grow faster than personal-vehicle VMT even without automated vehicles, the desired future for motorists and trucking companies is one of increased VMT on a much-improved major highway system. And by the time that the second-generation Interstate system is halfway into its development, both car and truck emissions will be on a long down-trend that could end up at zero—perhaps not fully, but already getting close by 2050.
Planning the next-generation highway system must take into account the transition to electric and automated vehicles, which is already underway. Increased VMT will not mean increased greenhouse gas emissions as this transition continues, urged on by federal and state policies.
Postscript: How Green Are Transit and Passenger Rail?
Back in 2008, the environmentally-friendly Union of Concerned Scientists produced a guide to the carbon footprint of inter-city trips by different modes, for individual travel and for a family of four. For a solo traveler, intercity bus had the lowest footprint, followed by airliner, which already by then was slightly less carbon-intensive than Amtrak’s mostly-diesel trains.
For a family of four, the results were even more dramatic. Again, the winner was intercity bus, followed by car, sport-utility vehicle, airliner, and again Amtrak in last place. Expanding Amtrak was not climate-friendly in 2008 and it is even less so today, as cars have become less polluting.
For urban trips, former U.S. Department of Transportation researcher Steve Polzin, in a just-released report for Reason Foundation, assembled 2019 data from the Department of Energy on the per passenger-mile of travel in gasoline gallons equivalent for urban travel options pre-COVID-19 pandemic. Polzin shows that rail transit had the highest, at 50.4 per-mile gasoline gallons equivalent, but current passenger cars had a respectable 41.7, slightly better than commuter rail (39.6), light trucks (36.1), and transit bus (26.6). Buses provide the large majority of U.S. mass transit service, and, over the next decade, cars are likely to catch up with and pass commuter rail, and potentially rail transit since those modes are unlikely to change while cars will get increasingly better.
So here again, as with highways, it would foolish to plan urban transportation on the assumption that mass transit will be more climate-friendly than personal vehicles. That is questionable today and will be highly unlikely by 2050.
A version of this column originally appeared in Public Works Financing.