Passenger cars have improved substantially, but heavier-duty vehicles have a long way to go, a new report shows.

(Michael Sivak and Brandon Schoettle, University of Michigan)

New cars, pickups, and SUVs sold in the U.S. have become remarkably more fuel-efficient, and their contributions to the national carbon footprint have declined significantly. In 1990, these vehicles represented 15.6 percent of total emissions in the U.S.; in 2014 they made up just 16.1 percent, according to a new report by Michael Sivak and Brandon Schoettle, researchers at the University of Michigan’s Transportation Research Institute. When you consider population, GDP, and car-sales growth over the same period, passenger cars have made major progress.

As an entire sector, however, transportation still has a long way to go in reducing emissions. That becomes abundantly clear when considering the growing impact of medium- and heavy-duty vehicles*. According to the same report, the share of total U.S. emissions from long-haul trucks, garbage trucks, ambulances and other types of five-ton-and-up mammoths has increased steadily and substantially, from 3.6 percent in 1990 to 6 percent in 2014. Absolute emissions from passenger vehicles leveled off over that period, but absolute emissions from heavier-duty trucks soared to 76 percent.

In their report, Sivak and Schoettle also highlight the major progress that industry—the sector that generates the most greenhouse gas in the U.S.—has made, with significant declines in both its absolute and relative emissions.

(Michael Sivak and Brandon Schoettle, University of Michigan)

Between that and improvements in passenger-vehicle efficiency, heavier-duty vehicles clearly have the most room to improve. At least in the short-term future, that could mean there will be a greater emphasis on heavy-duty vehicles as the U.S. strives to reduce greenhouse gas emissions. This will be long overdue, as these vehicles have managed to skirt efficiency improvements for years. As Julian Spector reported for CityLab in May, some engineers and entrepreneurs are beginning to confront the challenge, with innovations in battery technology, streamlined design, and calls for updated regulations around truck size and weight. With efficiency in heavy-duty vehicles astoundingly low as is, “even small improvements... can have a big effect on overall emissions,” Spector wrote.

None of this lets passenger vehicles off the hook, though, especially right now. Low gas prices have rekindled Americans’ love affair with SUVs and pickup trucks, the New York Times reported in late June. And though certain trends indicate that driving is on the decline, particularly among Millennials, that could change that in coming years as the U.S. continues to pull out of economic recession. To help avert climate-change disaster, trucks, and cars alike have a long road ahead.

*CORRECTION: An earlier version of this post inaccurately included buses as among the medium- and heavy-duty vehicles analyzed here.

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