Unless otherwise provided in this subtitle, upon approaching a railroad grade crossing, the operator of every commercial motor vehicle shall: Slow down and check that the tracks are clear of an approaching train; Stop before reaching the crossing, if the tracks are not clear; Attempt to negotiate the crossing only if the crossing and the roadway beyond the crossing are sufficiently clear of other traffic so that the driver can drive completely through and clear of the crossing without stopping; Obey a traffic control device or the directions of a police officer at the crossing; and Attempt to negotiate the crossing only if the vehicle has sufficient undercarriage clearance.