Don't be fooled to believe that your personal life-choices will make the difference. In most countries 50% of all emissions are determined by the electricity you are consuming with transportation coming in second.
The US used to be a railroad country. But that was bad for big oil, cars and aircraft so it was dismantled.
That alone cannot explain why the US pollutes twice as much. And as I have said, most of pollution comes from energy production. You are missing the mark.
However, your point is irrelevant as you have insufficient data to prove it. Stating that the average US citizen consumes twice as much is quite a daring that needs to be proven.
All of those things do matter. But of course they're not the whole story; plenty of industries pollute far more than consumers do. Regulations matter. And regulations, taxes and subsidies can do a lot to help both consumers and corporations to make better choices. I'd like to see heavy taxes on all fossil fuels, and the revenue from those taxes spent on increasing clean energy capacity.
Edit: my family has only one car, but it’s because I hate driving / commuting and have worked remotely for 10 years. If I had to drive to work, we’d have two cars.
Anyway, what's with this dichotomy "corporations should change behavior" vs. "consumers should change behavior"? Those two interact and influence each other. Obviously, both must change their behavior. This is a process that must be bootstrapped.
However, I don't like this frequently repeated claim that "it's actually big companies that are polluting!". They're polluting on our behalf, that's not an excuse.
You can also vote for more public transport, which most americans don't.
Edit: Since the maximum nesting was reached. I will leave it at saying that "A party system is twice as good as a one party system".