Interpretation ID: nht75-5.1

DATE: 04/28/75

FROM: NOEL C. BUFE FOR JAMES B. GREGORY -- NHTSA

TO: Hendrickson Manufacturing Company

TITLE: FMVSR INTERPRETATION

TEXT: I am writing in response to your letter of March 25, 1975, in which you request advice as to whether you should establish gross axle weight ratings and gross vehicle weight ratings based on the 55 mph national speed limit or on the maximum attainable speed of the vehicle.

The Cross Axle Weight Rating (CAWR) and the Cross Vehicle Weight Rating (CVWR) are defined by the National Highway Traffic Safety Administration (NHTSA) as determinations made by the manufacturer. (49 CFR 3571.3). As a general matter NHTSA finds that the manufacturer is most familiar with the complexities of this product and is most qualified to assign these values.

Recently NHTSA has found it necessary to specify that CAWR's and CVWR's be calculated on the basis of highway speeds and not qualified by reduced speed ratings; our reasons for this action are contained in the enclosed letter. For purposes of CAWR-CVWR calculations, NHTSA will hencefort consider "highway speed" to be the 60 mph value used by the United States Tire and Rim Association in assigning unqualified ratings to their tires.

Therefore, your trucks and buses which are capable of speeds of 60 mph or more should be assigned ratings which reflect vehicle capabilities at 60 mph.