Not going to defend NHTSA here, but it's a good idea to pass laws like this. NHTSA would likely have been sued if they passed the rule. Having a law really cuts down on the lawsuits.
After reading 5th Risk by Michael Lewis, I updated my thinking about government agencies. Government agencies are often quite limited by law and cannot advocate for effective policies. Lawmakers really should be updating rules much more often in consultation with agency scientists and specialists. I feel like we've gotten used to lawmakers not doing the jobs they are elected to.
I also believe that we should have a Greenhouse Gas Administration, and not rely on the EPA and Clean Air and Water Acts to cover CO2.