ignores inner bridge requirements and allows 48,000-pound tridems on non-IS highways. Given no Federally-imposed bridge formula, the State might choose to extend its bridge formula policy to Interstate highways. The other four States would probably proceed cautiously on liberalizing their bridge formula for the rest of their road networks. The most obvious prospects that could encourage relaxation of bridge formula provisions in the western border States would be:
A finding from Montana's current evaluation of Canadian RTAC weights that the formula is overly conservative, at least for certain bridge types and road classes.
A finding that Bridge Formula B leads to the use of excessively long drawbars in truck- trailer and double A-train configurations.
Pressure to relax Bridge Formula B weight limitation on tridem axles, and to allow effective use of tridems within a six-axle tractor-semitrailer combination. The seven- and eight-axle tractor-semitrailer combinations already operating in Washington, Idaho, Montana and North Dakota likely would be replaced with six-axle combinations given a more liberal bridge formula. These six-axle combinations should emerge as a popular unit for the farming industry (grain and fertilizer hopper bottoms), in livestock haul, in flat- deck operations (lumber haul), and for hauling fully-loaded 40-foot containers.
The Weight Aspects of the ISTEA Freeze: For the western border States, the ISTEA freeze prescribes the following State-specific GVW limits on the operation of “longer combination vehicles” (LCV). An LCV is a combination of a truck tractor towing two trailers which operates on the IS and weighs more than 80,000 pounds or three trailers at any GVW.
2 trailing units
3 trailing units
The GVW limits on all non-Interstate highways in these States, which is the case throughout the country, are determined by the individual States. The GVW limits for truck-trailer combinations and truck-trailer-trailer combinations, both on and off the Interstate highways in these States, is not controlled by the ISTEA freeze because truck plus trailer combinations are not “LCVs” as defined by ISTEA.
If Federal TS&W regulations were devolved to the States, and in so doing the ISTEA freeze were eliminated, the regulatory situation in these States would revert to what it was without the freeze.