U.S. highway vehicle growth trends – 1984-2021: What the numbers tell us

U.S. ground transportation is one of those areas over the years that has witnessed marked changes. Call it evolution. We who have paid attention, have seen a tug-of-war between modes. Railroads, for one, from the post-WWII years all the way up to and past the mid-1970s, experienced near-collapse. Transportation and energy emissions flip-flopped, energy being the lead emitter between 1978 and 2016, when the transportation sector emerged as the uncontested heavyweight champ and it’s been that way since. Transportation is responsible for contributing 28 percent of atmospheric greenhouse gas (GHG) emissions.

In this regard road transportation is the biggest culprit, one source telling me that roadway traffic accounts for as much as 80 percent of the GHG transportation-based contribution. If there is any good news in any of this it’s that transportation is working to clean up exhaust emissions some. The progress has, on the whole, been relatively slow-going, but, there is progress. Under the constant global warming and climate threats, will we see such efforts being substantially ramped up? That is the question.

That roadway-based modes of all modes (water, air. land) contribute most in the way of atmospheric GHG emissions, that this is the time of the year in the U.S. when there is much attention heaped on matters dealing with the quality of the air through events like Earth Day, Air Quality Awareness Week, with release of the American Lung Association’s annual “ State of the Air” report, and with the rise in highway vehicle numbers domestically and accounting for a quarter of the world’s 1 billion such vehicles, time has come again to take a close look at several aspects of that particular area. Whereas in the past here at the Air Quality Matters blog I’ve looked at considerations like vehicle miles traveled (VMT), gasoline consumption whether per vehicle or in the aggregate, fuel-economy or fuel-efficiency progress or even vehicle demographics such as the mix of low- or zero-polluting motor vehicles relative to all such vehicles on U.S. roads and things of this nature, today the area of concentration is on U.S. highway vehicle growth trends from the mid-1980s till present day. There is much that can be gleaned from this data.

An unprecedented presence and then some

In 2021 in the U.S., according to the U.S. Bureau of Transportation Statistics (BTS), there were a total of 282,366,300 highway vehicles. This compares to the 253,215,700 said vehicles on American roadways just 10 years earlier and the 235,331,400 in 2001. That’s a jump of 47,034,900 highway vehicles in two decades’ time or an average per-year increase of 2,239,757 said vehicles.

However, if we look at growth in percentage terms, between 2001 and 2011 and compare that to the period from 2011 to 2021, one will notice that in the case of the former, the rate of growth was 7.6 percent while in the latter instance, the rate of growth in highway vehicles is 11.5 percent; not quite double, but still considerable where percentage increases are concerned.

So, one may be curious how growth and percentage growth in highway vehicles in the 21st century compares to the same for the 1984-2000 timeframe. If there are significant differences, what could account for the changes?

For some background, it is helpful to remember that just prior to the arrival of the 1980s, there was an oil/petroleum embargo that made purchasing fuel for motor vehicle use a difficult proposition. Long lines of vehicles waiting in queues on the sides of roadways to gas up at gas stations was a common site. In response, there was much domestic interest in foreign-made imports due to their comparative fuel savings. All of this was going on right about this time. This is one particular factor that could have and probably did contribute to a heightened or sharp rise in the numbers of highway vehicles domestically.

In 1984, one study looking at registered light-duty vehicle numbers, in the United States at that time, there were roughy 159 million. Six years later in 1990, the number of U.S. registered LDVs was 22 million higher for a total of 181 million highway vehicles. The rate of such growth between those two years was recorded at 13.84 percent.

Meanwhile, from 1991 with a talley of right around 180.5 million registered domestic LDVs to 2001 its LDV numbers sitting at 220.5 million registered or thereabouts, the rate of growth in this second example is for the 40 million vehicle difference, an astonishing 22.16 percent gain, in fact, very close to twice the percentage growth increase of the 2011 to 2021 period mentioned above.

Just so we’re clear, for year 2011, the last year of the 2013 Sivak study*, U.S. registered LDVs totaled right around 234 million. This compares to BTS’ 253,215,700 highway vehicles of all types for that same year. In this instance, the roughly 234 million LDVs, represents 92.41 percent of all highway vehicles registered in the U.S.

So, what if anything does this say? Well, what it says to me is that the growth in registered domestic highway vehicles though still climbing is showing signs of slowing. This leaves one to ask why that is. Could the cost of gasoline have factored into this? One must remember that back in the early 1970s, the cost of gasoline was less than $1.00 per gallon. Between 1984 and 2000, there were relatively few mode options to choose from. So this no doubt meant a heavy reliance on roadway based modes.

In the 21st century meanwhile, a dearth in sufficient roadway capacity and the consequent gridlock and congestion that resulted on account of that, could have very well become a factor in the numbers of registered highway vehicles becoming fewer, larger percentages of former motor vehicle users seeking alternatives to single-occupant roadway vehicle use. I’m thinking ride-hailing, ride-sharing, walking, bicycling, public transit use as well as teleworking (also known as telecommuting or working remotely) are viable options. With presumed increased reliance on such alternatives, one would think there would be a corresponding improvement in air quality.

So, is this what we’re actually seeing? It could very well be.

Sivak, Michael, “Has Motorization in the U.S. Peaked?” UMTRI-2013-17, University of Michigan Transportation Research Institute, June 2013, p. 4

⁃ Alan Kandel

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Corresponding, connected home-page-entry image: U.S. Census Bureau