The issue is not passing safety tests (they do pass). The issue is, that these european manufacturers have to pass EPA/California emission certifications tests; they are not spending the money for it.
Examples. BMW 730 in diesel version is up to snuff in Europe, but has no appeal in the US. Drove a BMW 118cdi (turbodiesel) cabriolet during my last vacation in Europe (courtesy of an upgrade fom Sixt). Not offered in the USA, only the gasoline powered versions of the BMW 1 class. Speeds of > 100 mph were absolutely no problem for this 1.8 l turbo diesel.
Golf TDI's, Porsche Cayenne TDI, Audi A4. A6, A8 TDI, Mercedes TDI's, Ford, GM Opel and whoever (cars we can only dream of here in the USA), they are suitably certified for driving on the high-speed autobahns, but their engines are not paper-wise certified to comply with California emission tests (even if they would, the companies do not submit them). Speeds on German autobahns are in excess of the US 65 mph or slightly higher. If you drive at 65 mph, you will be in the slow lane and will be considered a "why is he/she driving that slow?" Significant speed limits do exist in Switzerland, France and some other Central European countries.
Whenever I arrive in Frankfurt and pick up my rental, and get on the Autobahn just south of the Frankfurter Kreuz, I have to control myself when stepping on the accelerator. Cruising along at an average speed of 140 km/h (= ~ 85 mph) is so comforting, and there is no problem accelerating to 160 or 180 km/h. You will get used to it. Yes, there are speed limits on the autobahns too, and you have to comply, but then you can get back to your normal cruising speed. The problem is when you come back to the USA.
Fuel consumption of these little beasts: they are in the >40 mpg class. New targets are set for 50 mpg or even higher by all the major European car manufacturers.
Regrettably they cannot be imported, as they do not have the proper paperwork.
