2.4.3 Effect of Combined Regulations
This section summarizes the combined defacto effects of the TS&W regulations that govern trucking operations across the western border.
Axle weight limits of 20,000 and 34,000 pounds on single and tandem axles respectively govern most trucking crossing the western border under regular operation. These limits apply to IS, NN and all principal State highways in the five border States. They are equal to (in the case of single axles) or more restrictive than (in the case of tandem axles) the equivalent limits specified for most connecting highways in Canada. The exceptions are: (1) the ISTEA permits trucks to move on I-15 between the Alberta-Montana border and Shelby, Montana at Canadian RTAC weight limits, (2) certain connecting secondary highways in Saskatchewan are restricted to axle weight limits of 18,000 and 32,000 pounds versus 20,000 and 34,000 pounds respectively for sigle- and tandem-axle limits, (3) certain highways in North Dakota are restricted to lower axle weights, (4) Idaho permits 37,800 pounds tandem axle weights for agricultural and mining-related trucks on the interstate if the GVW is less than 79,000 pounds, and (5) spring restrictions on certain roads, particularly in North Dakota.
Bridge Formula B governs most trucking crossing the western border under regular operation. Bridge Formula B is for the most part more restrictive than equivalent load distribution requirements specified for connecting highways in Canada. The exceptions are: (1) in North Dakota, a unique tridem limit of 48,000 pounds irrespective of spread is permitted on all highways other than IS highways; (2) in North Dakota, while the outer and inner requirements of Bridge Formula B apply to IS highways, only the outer requirements apply to non-IS highways; (3) the ISTEA permits trucks to move on I-15 between the Alberta-Montana border and Shelby, Montana at Canadian RTAC axle and GVW weight limits and RTAC inter-axle spacing provisions notwithstanding Bridge Formula B; (4) certain connecting secondary highways in Saskatchewan are restricted to tandem axle weight limits of 32,000 pounds; and (5) States enforcing inner bridge requirements are normally concerned only with the “trailer (as opposed to “tractor”) inner bridge,” which applies to the axle group including those from the second axle to the last axle.
The de facto GVW limit is at least 105,500 pounds for effectively all western border crossings except to and from Minnesota. A 131,060-pound limit applies in Montana, except for the special Shelby exemption of 137,800 pounds. Major highways in Minnesota are limited to 80,000 pounds GVW.
Split tandems are increasingly used in the western border States. Two axles on a semitrailer are spread by 10 feet, and as such are permitted 40,000 pounds of load (two axles at 20,000 pounds each) pursuant to Bridge Formula B. This arrangement allows operating five-axle tractor- semitrailers at a GVW of as much as 86,000 pounds where allowed and flexibility in loading at