From the Guardian, March 31, 2020: Trump to roll back Obama-era clean car rules in huge blow to climate fight (emphasis added):
The Trump administration is rolling back the US government’s strongest attempt to combat the climate crisis, weakening rules which compel auto companies to produce more fuel-efficient vehicles. [...] The changes to Obama-era regulations will allow vehicles to emit about a billion more tons of heat-trapping carbon dioxide – equivalent to roughly a fifth of annual US emissions.
Some are claiming that this change will directly result in the full billion tons of added emissions. But just because the requirement has changed, does not mean that automakers will automatically change the mileage or emissions controls on the vehicles they are producing. This is confirmed later in the article (emphasis added):
The Obama administration required auto companies to make vehicles 4.7% more efficient each year. The Trump administration initially wanted to freeze any progress on fuel efficiency past 2020. But its final rule, written by the EPA and the Department of Transportation, sets an improvement rate of 1.5% per year – or an industry average of 40.4 miles per gallon by 2026. That’s far less than the 2.4% per year by which the industry has said it will increase standards without any regulation.
Is there data or estimates on what the actual increase in emissions will be as a result of the new rule? Apparently the auto industry is capable of exceeding the current standard with no regulatory pressure, but will it now move the opposite way?