The driving on the interstate and defense highway system of this state of any vehicle or combination of vehicles exceeding the limitations of this section is hereby prohibited.

1. I. Maximum tire and axle gross weights allowable:

   1. (a) The manufacturer's load rating for the tires.

   2. (b) When being driven with a gross weight in excess of 73,280 pounds:

      1. (1) 20,000 pounds per axle on axles more than 8 feet apart;
      2. (2) 17,000 pounds per axle on axles not more than 8 feet apart;

   3. (c) When being driven with a gross weight not in excess of 73,280 pounds:

      1. (1) 22,400 pounds per axle on 3-axle single unit vehicles and on all other vehicles with axles 10 feet or more apart, including combination vehicles;
      2. (2) 18,000 pounds per axle on axles of vehicles less than 10 feet apart, except 3-axle single unit vehicles.
   4. (d) Two axles less than 40 inches apart shall be considered as a single axle unit.

2. II. Maximum allowable vehicle gross weights:

   1. (a) For 2-axle vehicles, 33,400 pounds.
   2. (b) For single unit 3-axle vehicles, 47,500 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is greater, as shown in table III.

   3. (c) For single unit 4-axle vehicles, provided that such vehicles shall have drive on 2 rear axles, and the tridem may contain not more than one retractable axle and, if not factory installed and load equalizing, must provide a system of load equalization by hydraulic, pneumatic, or mechanical means, and be equipped with brakes:

      1. (1) 47,500 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is the greater; or
      2. (2) If a heavy duty recovery vehicle, 75,000 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is the greater.
   4. (d) For a single unit 5-axle heavy duty recovery vehicle, 80,000 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is the greater. Such vehicles shall have drive on 2 rear axles, and the tridem may contain not more than one retractable axle and, if not factory installed and load equalizing, must provide a system of load equalization by hydraulic, pneumatic, or mechanical means, and be equipped with brakes.

   5. (e) For a combination of truck-tractor and semi-trailer equipped with 3 axles, the gross weight shall not exceed that set forth in table I as follows:

      Table I.
      Distance Between Extreme Axles in Feet	Maximum Gross Weight in Pounds
      25	54,500
      26	55,500
      27	56,000
      28	57,000
      29	57,500
      30	58,500
      31	59,000
      32	60,000

      Further provided that the maximum tire and axle gross weights as provided in paragraph I shall apply and the maximum load in pounds carried on any group of 2 or more consecutive axles shall not exceed that produced by application of the weight formula as defined in subparagraph (h).

   6. (f) For a combination of truck-tractor and semi-trailer equipped with 4 axles, the gross weight shall not exceed that set forth in table II as follows:

      Table II.
      Distance Between Extreme Axles in Feet	Maximum Gross Weight in Pounds
      28	60,500
      29	61,500
      30	62,000
      31	62,500
      32	63,500
      33	64,000
      34	64,500
      35	65,500
      36	66,000
      37	66,500
      38	67,500
      39	68,000

      Further provided that the maximum tire and axle gross weights as provided in paragraph I shall apply, and the maximum load in pounds carried on any group of 2 or more consecutive axles shall not exceed that produced by application of the weight formula as defined in subparagraph (h).

   7. (g) For a combination of truck-tractor and single semi-trailer with 5 or more axles with gross weight not in excess of 73,280 pounds, the weight on any single axle shall not exceed 22,400 pounds and the weight on any tandem axle shall not exceed 36,000 pounds.

   8. (h) For a combination of truck-tractor and single semi-trailer equipped with 5 or more axles with a gross weight in excess of 73,280 pounds or a combination of truck-tractor and more than one trailing unit, the total gross weight shall not exceed 80,000 pounds including all law enforcement tolerances, and the overall gross weight on a group of 2 or more consecutive axles shall not exceed that produced by application of the following formula, known as the weight formula:

      W = 500 { LN
      ——
      N − 1 + 12N + 36 } (In which W equals overall gross weight on any group of 2 or more consecutive axles to the nearest 500 pounds; L equals the distance measured to the nearest foot between the extreme of any group of 2 or more consecutive axles; and N equals the number of axles in the group under consideration.) Except that 2 consecutive sets of tandem axles may carry a gross load of 34,000 pounds each, provided the overall distance between the first and last axles of such consecutive sets of tandem axles is 36 feet or more and provided that such gross weight shall not exceed 80,000 pounds, including all law enforcement tolerances.

      The formula W = 500 { LN
      ——
      N − 1 + 12N + 36 } when expressed in tabular form results in maximum allowable load in pounds carried on any group of 2 or more consecutive axles as follows in table III.

      Table III.
      Distance*	2 axles	3 axles	4 axles	5 axles	6 axles	7 axles
      4	34,000
      5	34,000
      6	34,000
      7	34,000
      8 and less	34,000	34,000
      more than 8	38,000	42,000
      9	39,000	42,500
      10	40,000	43,500
      11		44,000
      12		45,000	50,000
      13		45,500	50,500
      14		46,500	51,500
      15		47,000	52,000
      16		48,000	52,500	58,000
      17		48,500	53,500	58,500
      18		49,500	54,000	59,000
      19		50,000	54,500	60,000
      20		51,000	55,500	60,500	66,000
      21		51,500	56,000	61,000	66,500
      22		52,500	56,500	61,500	67,000
      23		53,000	57,500	62,500	68,000
      24		54,000	58,000	63,000	68,500	74,000
      25		54,500	58,500	63,500	69,000	74,500
      26		55,500	59,500	64,000	69,500	75,000
      27		56,000	60,000	65,000	70,000	75,500
      28		57,000	60,500	65,500	71,000	76,500
      29		57,500	61,500	66,000	71,500	77,000
      30		58,500	62,000	66,500	72,000	77,500
      31		59,000	62,500	67,500	72,500	78,000
      32		60,000	63,500	68,000	73,000	78,500
      33			64,000	68,500	74,000	79,000
      34			64,500	69,000	74,500	80,000
      35			65,500	70,000	75,000
      **36			66,000	70,500	75,500
      **37			66,500	71,000	76,000
      **38			67,500	71,500	77,000
      39			68,000	72,500	77,500
      40			68,500	73,000	78,000
      41			69,500	73,500	78,500
      42			70,000	74,000	79,000
      43			70,500	75,000	80,000
      44			71,500	75,500
      45			72,000	76,000
      46			72,500	76,500
      47			73,500	77,500
      48			74,000	78,000
      49			74,500	78,500
      50			75,500	79,000
      51			76,000	80,000
      52			76,500
      53			77,500
      54			78,000
      55			78,500
      56			79,500
      57			80,000

      ^* Distance in feet between the extremes of any group of 2 or more consecutive axles.

      ^**Distance in feet between the extremes of 4 axles. (2 sets of 2 axles) 68,000 gross weight exception. The permissible loads are computed to the nearest 500 pounds.

   9. (i) The following loaded vehicles shall not be driven over H15-44 bridges:

      1. (1) A combination vehicle equipped with 5 axles in the configuration of 3-axle truck-tractor and 2-axle semi-trailer with wheel base less than 38 feet or 2-axle truck-tractor with 1-axle semi-trailer and 2-axle full trailer with wheel base less than 45 feet.
      2. (2) A loaded single unit vehicle with full trailer equipped with axles with wheel base less than 45 feet.
      3. (3) Vehicles with 7, 8, or 9 axles.
   10. (j) Coupled vehicles consisting of a truck together with a trailer attached to the truck by a pintle hook or similar coupling device with adequate breakaway protection as provided in RSA 266:63 may be driven, provided the total combined gross weight of the vehicles does not exceed 80,000 pounds and provided that each unit of the coupled vehicles shall be limited to the maximum permissible axle weights and gross weights of the individual units, and further provided that the weight of 2 or more consecutive axles of the coupled vehicle shall not be in excess of that produced by application of the weight formula as defined in subparagraph (h) and shall be limited to a total combined gross weight not in excess of 80,000 pounds, a single axle limit of 20,000 pounds and a tandem axle limit of 34,000 pounds.
3. III. Notwithstanding paragraphs I and II, for as long as exemptions exist in 23 U.S.C. section 127 that allow maximum gross weights of up to 99,000 pounds on interstate routes 89, 93, and 95 of the interstate and defense highway system, the provisions of RSA 266:18-a regarding weight on the non-interstate and general highway system shall also apply to vehicles or combination vehicles while being operated on any sections of interstate routes 89, 93, or 95 not posted by the commissioner of transportation for lower weights. Such vehicles shall not exceed the weight limits in paragraphs I and II unless they have been certified pursuant to RSA 266:18-d for the higher weights and paid the required fee the same as vehicles operating on the non-interstate highways as provided in RSA 266:18-d.

Source. 1921, 119:25. PL 103:22. 1927, 77:1. 1929, 33:1. 1933, 157:1. 1935, 133:1. 1937, 82:1. 1939, 131:1. 1941, 169:1. RL 119:37. 1947, 11:1. 1949, 104:1. 1950, 11:1, 2. 1951, 20:11. RSA 263:61. 1955, 230:1; 310:2. 1963, 189:1, 3; 202:1. 1973, 468:2. 1977, 487:1, 2. 1979, 219:1; 220:2; 239:1; 358:12. 1981, 55:1; 146:1. 1983, 434:15. 1986, 121:2. 1987, 404:20. 2005, 203:9, eff. July 1, 2005. 2018, 74:2, eff. July 24, 2018.