In a move to clarify enforcement practices, the Federal Motor Carrier Safety Administration is changing the definition of weight in single-unit trucks that are towing a trailer.

The final rule aims to provide an easy way to determine if a driver of this particular configuration must have a Commercial Driver’s License. It comes in response to a petition from the Commercial Vehicle Safety Alliance, which represents enforcement officers who have found it difficult to determine the status of these rigs.

The change concerns the relationship between “gross combination weight rating” and “commercial motor vehicle.”

It says enforcement officials can determine the GCWR from the certification label on the power unit. If that information is not on the label, the GCWR can be determined by adding the gross vehicle weights on the labels of both units. If the methods produce different numbers, the higher number will apply.

For details, see Wednesday’s Federal Register notice.