American Mobility in 2024

Using recent Department of Transportation data, I estimate that the average American traveled close to 18,000 miles in 2024. This is down from nearly 20,000 miles before the pandemic, a change that I’ll go into below.

American Airlines carried Americans more passenger-miles than any other airline in 2024. Photo by N509FZ.

Last week, the Bureau of Transportation Statistics released December air travel data indicating that the domestic flights carried people 800 billion passenger-miles in 2024. Since the Census Bureau’s latest population estimates say that the U.S. had 340.1 million people in 2024, that’s an average of 2,350 miles per person.

This doesn’t count 819 billion passenger-miles of international air travel, of which about 54 percent is by U.S. residents, according to the International Trade Administration. That represents an average of 1,300 miles per resident.

By comparison, travel by Amtrak is insignificant. The state-owned railroad’s monthly performance reports indicate that Amtrak carried 6.66 billion passenger-miles in calendar year 2024, which averaged less than 20 miles per U.S. resident. That means domestic air travel alone carried 120 times as many passenger-miles as Amtrak.

Airline flights tend to be longer than Amtrak trips, but for what it’s worth domestic flights carried Americans on about 26 times as many trips in 2024 as Amtrak. When international flights are added the ratio increases to 30 times.

As the airlines and Amtrak know how many people used their conveyances and where each person got on and off, all of these numbers are fairly precise. Public transit numbers are less precise and highway numbers are even more uncertain.

The Federal Transit Administration’s National Transit Database has published monthly ridership data for 2024 but has not yet published passenger-mile data. Transit passenger-miles are estimates anyway, because many transit agencies don’t keep track of exactly where every passenger gets on and off transit vehicles.

Based on the passenger-mile data reported in 2023, the average transit bus rider traveled 3.7 miles per trip while the average transit rail rider traveled 6.1 miles. Using average trip lengths for each mode — there are four bus modes, five rail modes, and several other modes including ferry boats — transit carried 7.4 billion riders a total of about 37.0 billion passenger-miles in 2024. That’s just under 110 miles per U.S. resident.

Auto and highway travel is the most important source of mobility by far but its data are the least precise. To calculate highway passenger-miles, we need to know how many vehicle-miles of travel there are, how those vehicle-miles are split up among cars, light trucks, motorcycles, buses, and heavy trucks, and how many people, on average, occupy each of those vehicle types. Errors can creep into all three steps.

The Federal Highway Administration uses a Highway Performance Monitoring System to estimate vehicle-miles of travel. This system consists of thousands of traffic counters distributed on freeways, arterials, and collectors all over the country. Notice there are no highway performance traffic counters on local roads and streets, yet the Federal Highway Administration says local roads carry about 13 percent of vehicle-miles. The agency relies on the states to provide those data and the reliability of the numbers vary by state. Besides that, the calculations converting traffic counts to vehicle-miles must be error-prone as well.

The next problem is estimating how many of those vehicle-miles were cars, how many were buses, etc. The Federal Highway Administration stopped sorting travel by “cars” and “light trucks” a few years ago and now uses “short wheelbase” and “long wheelbase” (short being 121 inches or less and long being greater than 121 inches) light-duty vehicles. According to 2023 data, short wheelbase vehicles account for 67 percent of vehicle-miles, long wheelbase 22 percent, heavy trucks 10 percent, and buses and motorcycles are each a little over half a percent.

Finally, passenger-mile data depend on estimates of average occupancies for each of these vehicle types. Since 1969, the Federal Highway Administration has conducted a travel survey about every five years that asks, among other things, about vehicle occupancies. In 2017, the survey collected data from 130,000 households, but for various reasons its sample size in 2022, the latest survey, was only 7,500 households.

For most recent surveys, the average occupancy of private vehicles was a little more than 1.6 persons. In fact, it was 1.67 persons it both the 2009 and 2017 surveys. In 2022, however, the average occupancy dropped to 1.52.

I can see where the pandemic might have reduced occupancies by reducing carpooling. However, carpooling represents only a small fraction of total vehicle travel. The increase in remote working has also changed vehicle travel, but total vehicle miles have not changed. Since fears about disease transmission have declined, I don’t know why occupancies would be much different in 2024 than they were in 2019. However, the Federal Highway Administration is using the lower 2022 number in all its recent estimates of passenger-miles.

Long wheelbase vehicles have higher capacities than short wheelbase vehicles, and this is reflected in higher vehicle occupancies in the 2017 travel survey. Since the 2022 travel survey, however, the Federal Highway Administration has assumed that long wheelbase vehicles have lower average occupancies than short wheelbase vehicles. I suspect that is an error that is probably due to the smaller sample size of the 2022 survey compared with the 2017 survey.

Another source of error is occupancies of rural travel. Nearly all of the travel survey data , including automobile occupancies, are based on urban travel, which is 71 percent of the total. For intercity travel, cars and light trucks have been estimated to carry an average of 2.2 to 2.4 people, but no one keeps track of this on a regular basis and the Federal Highway Administration uses the urban vehicle occupancy for all travel.

Estimates of bus occupancies are even more questionable. Back in 1989, someone at the Federal Highway Administration guesstimated that the average bus carried 21.2 people, and that number has been used ever since. Based on this and the number of vehicle-miles attributed to buses, the Bureau of Transportation Statistics estimated that non-transit buses carried 380 billion passenger-miles in 2022. Considering that school buses, intercity buses, charter buses, and other motor coach travel amounted to a little more than 100 billion passenger miles before the pandemic (when the Bureau of Transportation Statistics estimated that non-transit buses carried about 360 billion passenger-miles), there appear to be as many as 250 billion ghost-miles of bus travel.

The Federal Highway Administration assumes that heavy trucks have just one occupant, and since those occupants are mostly paid professional drivers, not passengers, I don’t count them in the totals. I do count motorcycle numbers but they are small. Otherwise there are clearly a lot of potential errors in the data.

Using 2024 vehicle-mile data, the 2023 breakdown of vehicle-miles by type of vehicle, and the 2022 occupancy estimates, Americans traveled 4.8 trillion passenger-miles on highways in 2024. That’s a little more than 14,000 miles per person, which compares with 16,000 miles before the pandemic. Most of this decline is due to the drop in estimated vehicle occupancies.

I’m not going to try to correct these numbers, but if occupancy estimates are too low, then Americans probably traveled as many miles by auto in 2024 as before the pandemic. Beyond this, I am pretty sure the bus vehicle-miles are too high, which — because all vehicle-miles must add up to a predetermined total — means the light vehicle miles could be too low. I suspect the light-vehicle occupancies are too low for several reasons, and I’m particularly suspicious of the small sample size in the 2022 travel survey. It would also be nice to have more reliable data about rural vs. urban vehicle occupancies and updated data on bus occupancies as the bus industry has radically changed since 1989.

Even at the lower occupancies, motor vehicle travel is four times as great as air travel and completely swamps all other forms of travel. The 71 percent of passenger-vehicle travel that takes place in urban areas represents almost 100 times as many passenger-miles as transit. The 29 percent of passenger-vehicle travel that takes place in urban areas represents more than 200 times as many passenger-miles as were carried by Amtrak.

While we don’t have recent data for other countries, data from a few years ago indicates that automobile travel in European countries averaged around 6,000 miles per person. The only countries that come close to the U.S. are Iceland, Canada, and possibly Australia and New Zealand, and even they are only about 10,000 miles per person.

The main reason auto travel is lower in other countries is not the availability of bus and rail alternatives but higher fuel taxes. Gasoline taxes in most European countries are close to ten times as much as in the U.S., while in Japan they are four times as much.

A large share of the fuel taxes in other countries effectively subsidizes rail and bus travel, but lower auto travel is only partially made up for by increased trains and buses. Together, these modes averaged about 1,300 miles a year in European countries, including both urban and intercity travel. This means European residents have typically lost 8,000 miles of auto travel to gain 1,300 miles of other forms of travel, which doesn’t seem like a good trade-off.

Other than for Amtrak, information about subsidies to the various modes is not yet available. Based on previous years, I estimate 2024 subsidies to public transit will average more than $2 per passenger-mile; subsidies to Amtrak are around 35¢ a passenger-mile; and subsidies to air and auto travel will average around 1¢ per passenger-mile. Even if all subsidies are eliminated, automobiles and airlines will remain the predominant forms of travel in the United States for many years into the future.