Yes. The main killer for cars, even on highway driving, is the frequency of acceleration. Trains have very smooth acceleration/deceleration profiles, which makes them easy to optimize. When they don't, something has generally gone very wrong.

With cars... Well, think about how you drive on the highway. Your speed's usually about the speed limit. Sometimes you drift a little higher, sometimes a little lower. Sometimes you make really sharp changes in speed, like when you come over that hill and see Granny McBloggs putting along at a positively mind-boggling 50 km/h, and again when you pull out to try and pass her. It's better than city driving, but it's still pretty nasty compared to a good train system.