“It’s a very emotional topic,” confided Stefan Gerwens, the head of transport and mobility at ADAC, an automobile club with 20 million members, which is opposed to any speed limit.

So emotional, apparently, that facts and figures count for little.

Germany is woefully behind on meeting its 2020 climate goals, so the government appointed a group of experts to find ways to lower emissions in the transport sector. Cars account for 11 percent of total emissions, and their share is rising.

A highway speed limit of 120 kilometers an hour, or 75 miles per hour, could cover a fifth of the gap to reach the 2020 goals for the transport sector, environmental experts say.

“Of all the individual measures, it is the one that would be the most impactful — and it costs nothing,” said Dorothee Saar, of Deutsche Umwelthilfe, a nonprofit environmental organization that has lobbied for a speed limit.

“But when it comes to cars,” Ms. Saar sighed, “the debate tends to become irrational.”

There are already speed limits on almost 30 percent of roughly 8,000 miles of autobahn, imposed to regulate noise near urban centers and reduce safety risks on roads deemed unfit for unlimited speeding. The number of deadly accidents on stretches of autobahn that have a speed limit is 26 percent lower than on those without.

In 2017, 409 people died on the autobahn and in almost half the cases, the reason was inappropriate speeding, according to the German statistics office.