Network Rail have already worked with Top Gear to show the dangers of a car being struck by a train on a level crossing, by propelling a 31 at a fair rate of knots into a people carrier on NR metals, somewhere in Lincolnshire I believe.
It was filmed here on the B1206 between Hibaldstow and Brigg in N. Lincolnshire on the line between Brigg and Kirton (in) Lindsey. I used to use that LC a lot around that the time as I was working up that way. The passenger service there is Saturdays only iirc, so I guess it would be a good location to film the crash without causing major disruption.