Why does the auto industry prefer uniform (national) standards for automobile emissions as opposed to regionally varying standards? Are uniform standards beneficial to everyone?

For automobile emission, a uniform standard is preferred, because no unnecessary advantage is given by it to any company that is located in particular states where the regional standards are less severe.

Since pollution has its impact across the states and in the whole of the USA, then there should be uniform standards across all the states. It will also invalidate the impact of regional standards as a factor in the selection of plant locations for the automobile company. It means that a state offering less valid emission standards, will attract more companies to herself and it will be against the other states who care more about the natural environment. It can make more states to opt for the permissive emission standards, that will be more harmful to the USA as a country, than the good. So, a uniform standard is preferred to eliminate it as a factor in plant location decisions.

Yes, uniform standards are beneficial to everyone, because it will bring effective control upon the pollution level because there will be no state where the culprit firm can hide. Besides, it is more effective as efforts done towards environment conservation.