1. I'm sure that UP has no problems with cops chasing after thieves on UP property.Part of the situation comes about because the rails are not nationalized. Essentially, the rails are private property, and the police cannot patrol them. If they were nationalized, like the highways, they could be openly patrolled but the railways could not have people "trespassed" from them like they do now.
It can be a Catch 22 situation
2. UP, even though it is a private company, has its own railroad police, which has full peace officer authority, so UP bulls can also chase after thieves and make arrests.
As Pewee TM mentioned, they've had this sort of problem in the past in other countries where the railroads are government owned.