As used in this subpart:

1. (1) “Dolly” means a device, other than a trailer or semitrailer, attached to one (1) or more axles which, when connected to a vehicle or combination of vehicles, carries a portion of the gross weight of the vehicle or combination of vehicles;
2. (2) “Federal bridge formula” means the maximum weight in pounds that can be carried on a group of two (2) or more axles using the following mathematical formula: W = 500 x [LN / (N-1) + 12N + 36] W = the maximum weight in pounds that can be carried on a group of two or more axles to the nearest 500 pounds. L = the distance in feet, measured from center of axle to center of axle to the nearest foot, between the extremes/outer axles of any group of two or more consecutive axles. N = the total number of axles in the group under consideration. The numbers in the above formula (500; -1; 12; and 36) shall be constant numbers.
3. (3) “Front or steering axle” means a front or steering axle attached to the front of the vehicle and which is used to steer the vehicle on a given path or direction;
4. (4) “Gross weight” means the combined weight of a vehicle or vehicle combination without load and the weight of any load thereon;
5. (5) “Lift axle” means any load-carrying axle permanently attached to a vehicle or dolly so as to make possible the raising or lowering of the axle and which can affect the amount of weight carried by that axle or other axles;
6. (6) “Quadrum axle” means any four (4) consecutive axles whose extreme centers are not more than one hundred ninety-two inches (192") apart and are individually attached to or articulated from, or both, a common attachment to the vehicle including a connecting mechanism designed to equalize the load between axles (for illustration, see Appendix 5);
7. (7) “Single axle configuration” means two (2) consecutive front or steering axles whose centers may be included between parallel transverse planes and which are spaced forty inches (40") or less apart;

8. (8)

   1. (A) “Single load-carrying axle” means a load-carrying axle other than a front or steering axle which is permanently attached to a vehicle or dolly and is designed to carry a portion of the gross weight of a vehicle or combination of vehicles.
   2. (B) A group of two (2) or more axles in which the outer two (2) axles measure less than forty inches (40") from the centers of the axles shall be considered a single load-carrying axle for all purposes.
   3. (C) A load-carrying axle shall have a minimum capacity rating of eighteen thousand pounds (18,000 lbs.).
   4. (D) Measurements shall be made from the center of axle to center of axle to the nearest inch (for illustration, see Appendix 5);
9. (9) “Tandem front or steering axle configuration” means two (2) or more consecutive front or steering axles whose centers may be included between parallel transverse vertical planes spaced more than forty inches (40") apart and not more than ninety-six inches (96") apart and extending across the full width of the vehicle (for illustration, see Appendix 5);
10. (10) “Tridem axle” means a group of three (3) consecutive load-carrying axles which are permanently attached to a vehicle or dolly and any two (2) of which are in tandem, in which the outer axles are no less than ninety-seven inches (97") and no farther apart than two hundred four inches (204") when measured from the center of axle to the center of axle to the nearest inch (for illustration, see Appendix 5);
11. (11) “Trunnion dolly assembly” means any dolly unit consisting of trunnion wheel combinations that may be connected by steel beams or be used to support loads at extreme ends; and
12. (12) “Trunnion wheel combination” means independent wheel assemblies designed with hydraulic suspension cylinders and located transversely across from each other to form an axle combination.