It's best to stay at least ten feet away from the nearest rail.
50 feet
40 is the nearest 10, so it is 3 away from it.
1mm
Two away
The Pennsylvania's Driver's Manual states that driver's cannot park within 50 feet of the nearest rail of a railroad crossing.
4.2 light years away
3 3 away from 80 7 away from 90
2000
The nearest star is about 4.2 light years away. So; 39,734,219,300,000 kilometres
The tube (underground) doesn't go out as far as Bexley but Bexley has its own rail station.
The nearest black hole to Mercury is about 1600 light years away.
Proxima Centauri, and its 4.2 light years away.