Which of the following vehicles must still comply with the mandatory stop-look-listen procedure at a railroad-highway grade crossing under 49 CFR 392.10, even though it is completely empty and unplacarded at the moment?

49 CFR 392.10(a)(4)

Drivers sometimes assume that an empty tank means the hazmat rules don't apply anymore, but residual vapors and coating inside an 'empty' cargo tank can be just as dangerous as a full load in a collision. That's exactly why the regulation covers cargo tanks whether loaded or empty — the stop requirement follows the vehicle's hazmat use, not whether there happens to be product in it right now.