The BTTF films are widely regarded as movie Classics, so there is a lot of interesting info. available about the making of them, something I too find very fascinating.
I found this on IMDB trivia for BTTF3:
"The Delorean's wheels are conveniently located for riding on railroad tracks. The car's track width is 62.6", and the front wheels are 6" wide. The standard gauge used on U.S. railroads is 56.5""
Mind you, I don't really understand it... Does that mean the centre lines of the wheels are 54.6 inches apart? A diagram would help!