You are approaching a railroad crossing. The flashing lights and warning bell are NOT activated at this moment. Which of the following are true?

School buses and trucks carrying hazardous materials (such as gasoline) are required to stop at railroad crossings even if the tracks are clear. You should follow these vehicles at a safe distance and be prepared to stop. Don't start to cross railroad tracks if the railroad crossing gates or warning signals are activated. Bear in mind, however, that warning signals can be malfunctioning or broken. Even if the warning signals are not activated, don't start to cross the tracks if you see a train approaching, especially if the train is sounding its horn. Federal regulations require an approaching train to sound its horn when it is only 15–20 seconds from the railroad crossing. If you must stop, remain between 15 and 50 feet from the nearest rail. [Stop at Railroad Crossings, Stopping Regulations, Chapter 4: Safe Driving Rules & Regulations, The New Jersey Driver Manual], [49 CFR 222.21]