Automakers don’t like uncertainty. That is understandable for an industry making design decisions today about the cars and trucks of the next decade. At the same time, the companies know they cannot erase all uncertainty. So they are especially keen on keeping to a minimum the unnecessary, or self-inflicted, kind. Which gets to the promising deal four of the world’s largest automakers recently struck with California.

The agreement involves fuel-economy standards for cars and trucks. Ford, Honda, Volkswagen and BMW will make steady increases in efficiency with the goal of reaching 51 miles per gallon across their fleets by 2026. In return, the companies are looking for other automakers to join the deal, knowing the significance of the California market (the largest in the country for cars and trucks) and the state’s authority, going back five decades, to set its own more restrictive rules for vehicle emissions.

The automakers know something else: Improved fuel-efficiency is a good thing, and not just for combating climate change, with transportation now the country’s largest source of carbon emissions. The pursuit of efficiency fuels innovation in the manufacturing sector, say, in lighter materials or parts that reduce friction. It advances the supply chain, many of those small- and medium-sized businesses located in Ohio.

What brought California and the automakers together? The answer goes back to the Obama White House in the aftermath of the auto rescue, reaching an agreement with car companies to attain fuel economy of 54.5 miles per gallon by 2025. All parties applauded. Yet when President Trump arrived in office, automakers asked him to take a look at adjusting the rule, in part, because consumers continue to show a preference for SUVs and pickup trucks, which have lower fuel economy.

The automakers were seeking some flexibility. What they got is much more than they sought.

The Trump administration has launched an effort to roll back the Obama standard to 37 miles per gallon. It expects to complete the rule later this year, arguing, weakly, that the higher standard would discourage car buying, resulting in more motorists driving older, less safe cars. Actually, leaked emails from the Environmental Protection Agency reveal that analysts calculated the rollback would lead to more deaths.

The administration also appears set on seeking to revoke California’s authority to set its own emission standards.

All of this worries automakers. They see a prolonged legal fight with California. They already have invested heavily in retooling their operations based on achieving steady increases in fuel economy. They know that 13 other states have joined California in complying with higher fuel-economy standards. Thus, if California prevails in court, and keeps its authority, while the Trump administration holds to its rule, automakers would see a divided domestic market, requiring the costly step of producing two lineups of vehicles.

Automakers pressed the administration to seek a deal with California to secure one national market. The administration ended the talks in February. In June, 17 automakers sent a letter to the White House explaining that its plan for fuel-economy standards would reduce their profits and produce “untenable” instability in the industry. The administration’s dismissive response persuaded the car companies to approach California.

From the state, the four automakers get the leeway they need, for instance, gaining credits for fuel-saving technology. Yet the 51 miles per gallon fits into a global market in which countries are requiring similarly high fuel-economy standards. The agreement is good for the companies, the environment and the economy. It provides, as the four put it in their statement, “much-needed regulatory certainty.” At this point, the Trump White House could help by urging other automakers to join.