Diesel cars and emissions standards in US vs Europe

Factual Questions
1

I was watching some show on PBS with Alan Alda about future car technologies. It was mentioned in passing that diesels are great but that the same engines that are popular in Europe can’t be used here in the US due to emissions standards.

This raises a couple of obvious questions:

  1. How does the US have higher emission standards than a place with a viable Green party?
  2. What about the diesel cars that are actually sold here (like the VW TDI ones)?
2

Perhaps surprisingly, this difference does seem to exist, stats appear here.

My WAG is that the US has had to focus on diesel emissions because of a greater reliance on road transportation of freight. And I do wonder how the petrol emission regulations compare…

3

I think that the fuel used in Europe is low sulphur diesel. The diesel in the states has much higher levels of sulphur. While cars like the VW TDI can meet current emission standards in most US states (I think it fails in California, maybe a few other states), proposed standards in the future will be harder to meet with high sulphur fuel.

I’d imagine that the sulphur levels could be reduced, with an increase in price, if the market (or more likely, regulations) demands it. I hope so, I like the TDI over a hybrid.