[oposa]

You can, because you just have to make them fast enough to be competitive. Really fast train will probably never be widespread because they require to much infrastructure. A train going 5 times the speed of a car requires a lot of very expensive track per hour of travel. That is why the Chinese maglev only travels ~1 minute at top speed. But going 2 to 3 times the speed of a car is competitive as the tracks are cheaper and airplanes are expensive (both in cost and time) to stop. It all of course depends on local factors, but from 2 times the speed of a car trains start taking a lot of passengers from airplanes.

(There is also other benefits, like that trains don't generally go away. There are many places in Europe that are relatively hard or expensive to fly to).