WASHINGTON (AP) — Pollution from diesel trucks, buses and cars globally is more than 50 percent higher than levels shown in government lab tests, a new study says.

That extra pollution translated to another 38,000 deaths from soot and smog in 2015, the researchers estimated.

The work published Monday in the journal Nature was a follow-up to the testing that uncovered the Volkswagen diesel emissions cheating scandal. Researchers compared the amount of key pollutants coming out of diesel tailpipes on the road in 10 countries and the European Union to the results of government lab tests for nitrogen oxides.

They calculated that 5 million more tons (4.6 metric tons) was being spewed than the lab-based 9. 4 million tons (8.5 million metric tons). Governments routinely test new vehicles to make sure they meet pollution limits.

Experts and the researchers don’t accuse car and truck makers of cheating, but say testing is not simulating real-world conditions.

“The paper shows how much human failure costs,” said Jens Borken-Kleefeld, a transportation scientist at the International Institute for Applied System Analysis in Austria who wasn’t part of the study.

The researchers included a team from the International Council on Clean Transportation, a nonprofit research and advocacy group, that arranged the testing that first showed VW diesel cars were rigged to cheat on emissions tests. They used previously published tests of pollutants coming from thousands of vehicles, all models, to calculate the extra pollution in 2015. Worldwide, three-quarters of that extra pollution is from trucks and buses.

Other research connects soot and smog to heart and lung diseases, with pollution killing more than 4 million people every year around the world, said lead author Susan Anenberg, a researcher at Environmental Health Analytics and a former U.S. government scientist.

The researchers calculated that the extra nitrogen oxides were responsible for about 31,400 deaths in 2015 because of tiny soot particles in the air and 6,600 deaths from extra smog.

The European Union, which has mostly diesel cars, had an extra 11,500 deaths; China, 10,600; India, 9,300; and the United States, 1,100.