This is just speculation based on the FAQ, but it looks like the perfect set of circumstances where the bridge can't be modified, the road can't be modified, and I'm suspecting there's not really a good place to put a turnoff let alone a place to reroute the train tracks altogether. In at least one part of the video you can see a guy realize his mistake just before crashing into the bridge, stop and try to turn around, only to find there's nowhere to go. You'd think truckers in the area would at least be aware that there's a cursed bridge in the area that eats trucks and that rental companies would warn people about it.