In the countries I've lived and driven in, I've noticed some differences between how people drive on the motorway (that's like the "interstate" for you yanks). In England, people tend to drive with an unparalleled politeness. They will happily move over to let you pass, make room for you to merge in, or brake so you can change lanes ahead of them. Spaniards, on the other hand, are just as selfish as the Brits are selfless. In Spain, everyone assumes that you will also behave selfishly, so when you try to be polite to other drivers, they get confused or don't trust that you're really letting them merge. The Americans are somewhere in between. One difference I've noticed between driving on the motorway in Spain and the US is the speed at which the drivers in the fast lane pass me. It's quite common in Spain for a car to pass by going more than 15 kph faster, whereas that isn't very common at all in the US. I think this is partly due to the ubiquitousness of cruise control in American cars. Cruise control, like automatic transmission, is a fairly high end option on cars in Spain still, whereas they are the defaults in the States. When you're driving on the motorway without cruise control, it's very easy to let your mind wander and end up either 20 kph above or below the speed limit.
From my casual observations, which are probably riddled with confirmation bias, the cars that whiz past me in the fast lane are almost always, say nine times out of ten, either an Audi, a Mercedes, or a BMW. My theory on why this might be so goes something like this...
Car manufactured in Germany are designed with the speed limitless autobahn in mind and are thus more comfortable to drive at very high speeds than cars manufactured outside of Germany.
Not only is it that the ride is smoother at high speeds, but that the speedometer is designed to go higher. I recall my grandmother reporting some years back that after changing cars, she noticed that she drove faster on the motorway. Eventually she figured out that she had become used to keeping the speedometer needle exactly vertical, which was 100 kph in the old car and 120 kph in the new one. I think there's definitely something to that.