I think the disabled trains would make it more challenging. You don't get a clear run, or maybe you have to move a switch track lever to get around them. And in fact the switches could be part of the strategy, you come down a hill, and you don't know that some bandits have switched to the track to a waiting ambush. I think the main point of my suggestion is that are survivor-powered, and that cooperative play makes them more useful (cooperative either someone working switches or helping to pump the handcar).

I'll go and survey the tracks, but at a lot of stations in real life there are typically parallel tracks for shunting and so you could get around the trains that way.