A couple of observations:
Where I live, the Border Patrol has direct communication with the UP Railroad. It's used to coordinate train stops for inspections, but I suppose they could use it in an emergency.
In commuter rail territory in NYC, Chicago, etc., rush hour headways are very short. If something happens on the right-of-way in this scenario, a telephone call to the local police just isn't going to avoid a possible disaster in many cases. Seconds count in this situation.
A cellphone call to the railroad emergency number that's posted on the crossing control box is fine, but that doesn't work if no one has a cellphone, or if the emergency in question is not at a crossing.