US car companies and importers have written a letter to US President Donald Trump that appeals for a middle way on emission and mileage standards to avoid the danger and uncertainty surrounding the possibility of two de facto standards – one that covers most US states and a tougher one involving a group led by the state of California.

A group of 17 automakers – including importers as well as Ford and GM but not FCA – has asked Trump to abandon plans to completely scrap current emission standards that were set by the Obama administration. Although the auto industry dislikes those (seen as tough targets), the auto industry group wants a compromise that avoids scenarios of extended uncertainty or two sets of emissions standards applying in different parts of the country.

The letter said: "The question of the right level of regulation is complex. What works best for consumers, communities, and the millions of US employees that work in the auto industry is one national standard that is practical, achievable, and consistent across the 50 states."

The US state of California  – followed by twelve other US states – has said it plans to keep tougher regulations in place. The US federal government and California are already in a legal battle over whether California can keep the tougher standards.  

The automakers say they need regulatory certainty and are calling for a single standard that includes reductions to greenhouse gas emissions that are 'midway' between a Trump administration proposal that would freeze emission requirements at 2020 levels through 2026 and the Obama administration's tougher standard that require average annual improvements of around 5% through the period.

The automakers want the US federal government and state of California to resume discussions to develop a compromise single national standard.