How fast can you go in one of those pickups with the train wheels???
How fast
can you go? Or how fast are you
allowed to go. The pat answer for both is "it depends". It's different depending on what track you're on, and things may have changed since the last time I had anything to do with hi-rail vehicles, but the fastest I recall being allowed to go by rule was 40 mph. If you think the rules don't apply, then.....fast as you dare. Better not get too daring. It's pretty easy to derail those things.
