It is known that a Immovable Rod will deactivate if more than 8,000 lbs of weight is put on it. So, prompted by this question and some of the answers on it. I "asked my GM" and he told me to ask here (i swear).
If we assume that the rod is stationary to the ground and not the vehicle, meaning that the rod remains in place while a locomotive moves (as seen on the this answer for that question), so the rod would be pushed against one of the inside doors, how much weight could this door withstand before breaking down? Or would the rod deactivate against the tractive force caused by the locomotive against the rod?
To put it into another perspective (excuse me if it's wrong, not a physics expert), would an object that weights 8,000 lbs at x miles/hour be enough to bring down a wooden/iron door?
For the sake of this question, let's consider both wooden doors from earliest locomotives and iron doors from the modern ones. If it's not possible to figure this out due to lack of rules, answers with backup from previous editions are acceptable.