Max Legal Weight for GVW under 80,000 lbs and Max Permitted Weight for GVW over 80,000 lbs
22,400 pounds on all vehicles w/axles 10’ or more apart (including combination vehicles) except as noted for 4-axle single unit vehicles.
18,000 pounds/axle on all vehicles except for 3 and 4 axle single unit vehicles.
For combination of tractor-trailer and single semi-trailer w/ 4 or more axles.
Maximum on tandem: 36,000 pounds
Maximum on tridem: 54,000 pounds
Gross Vehicle Weight
Two Axle Truck – 33,400 lbs.
Three Axle Truck – 55,000 lbs., 22,400 lbs./axle max
Four Axle Truck – 60,000 lbs., 18,000 lbs./axle
Two Axle Truck – 37,400 lbs.
Three Axle Truck – 65,000 lbs., 22,400 lbs./axle max
Four Axle Truck – 73,000 lbs., 20,000 lbs./axle
3 Axle Tractor Semi-Trailer – 54,500 – 60,000 lbs. (D=25 ft. – 32 ft.)
4 Axle Semi-Trailer – 59,000 – 69,000 (D = 8 ft. – 18 ft.)
5 or 6 Axle Semi-Trailer – 70,000 – 84,000 lbs. (D=19 ft. – 29 ft.)
86,000 – 99,000 lbs. (D = 30 ft. – 36 ft.)
6,7 or 8 Axle Semi-Trailer – 86,000 – 99,000 lbs. (D=30 ft. – 36 ft.)
Note 1) RSA 266:18-c states that a vehicle or combination of vehicles shall not be driven or moved over any bridge or other structure on any way if the weight of such vehicle, or combination of vehicles and load, is greater than the capacity of the structure as shown by a sign on the right side of or overhead on the structure. It is assumed that the weight of the OS/OW permit vehicle will be in excess of the provisions of RSA 266:18-b, and therefore will exceed the posted capacity of the bridge.
Note 2) For purposes of this table, axles together are considered a group of axles (tandem, tridem, quad, etc.) when each individual axle space in the group is less than 10'-0".
Note 3) Speed of permit vehicle shall not exceed 20 miles per hour while crossing bridges (except for bridges on the interstate and turnpike system, or corridors designed to meet interstate standards...including NH101 from Manchester to Hampton, etc.).
Source of information: https://www.nh.gov/dot/org/operations/highwaymaintenance/overhaul/documents/overweightloadbridgecriteriasheet.pdf