RSA 259:107-a: Tandem Axle.

"Tandem axle" shall mean 2 consecutive axles whose centers may be included between parallel vertical planes spaced at least 4 feet and not more than 10 feet apart, extending across the full width of the vehicle, except that for vehicles being driven on the interstate and defense highway system with a gross weight in excess of 73,280 pounds a tandem axle shall be limited to 2 or more consecutive axles whose centers may be included between parallel vertical planes spaced not less than 40 nor more than 96 inches apart, extending across the full width of the vehicle.