Why should a driver treat a private, unmarked railroad crossing, such as one on a rural road, with the same caution as a fully signed public crossing?

Correct answer to question 152 (Passenger): A lack of official signage does not mean a train is any less likely to be present

Why

The absence of official signage at a private or unmarked crossing does not reduce the actual risk of an approaching train, so the same careful stop-look-listen approach should be applied there as at a fully marked crossing.