RSA 266:11 Length.

The driving on ways of this state of any vehicle or combination of vehicles whose length including load exceeds the limitations of this section is hereby prohibited:
I. For a single unit vehicle or a bus, 45 feet including front and rear bumpers.
II. For a semi-trailer in a truck-tractor, semi-trailer combination, 53 feet, except that any semi-trailer in excess of 48 feet shall not be operated if:
(a) The distance between the kingpin and the centerline of the rear axle or the midpoint of a tandem axle of the semi-trailer exceeds 41 feet;
(b) The semi-trailer is not equipped with a rear end protection device of substantial construction consisting of a continuous lateral beam extending to within 4 inches of the lateral extremities of the semi-trailer and locate