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OCR for page 47
47
requires that no jurisdictions have more restrictive dimensions tri-axle semitrailer, where the semitrailer had a single liftable
than the national standard. This allows vehicles meeting the di- axle ahead of a fixed tandem axle. The semitrailer had some
mensions of the national standard to travel in all jurisdictions. slight dimensional differences between provinces and was al-
A jurisdiction may be more liberal than the national standard, lowed a gross weight of 49,000 kg (108,025 lb) in Nova Sco-
for its own purposes, as it knows that other jurisdictions are not tia and New Brunswick, about 51,000 kg (112,434 lb) in
obligated to accept such vehicles. A jurisdiction would always Québec, and about 52,500 kg (115,741 lb) in Ontario. How-
remain at liberty to restrict roads to vehicles with lesser dimen- ever, Nova Scotia had a legislated gross weight tolerance of
sions than the national standard in cases where road conditions 3,000 kg (6,614 lb), New Brunswick had an administrative
are not suitable for larger vehicles, such as, for example, in Cal- tolerance of the same value, Québec had a mandatory admin-
ifornia, where a number of mountain roads are restricted to istrative tolerance of 1,500 kg (3,307 lb), and Ontario had an
semitrailers no longer than 8.53 m (28 ft). administrative tolerance at the discretion of the officer, which
Dimensional compatibility must extend beyond overall industry generally considered zero. When the tolerance in
length, and must also include regulated internal dimensions. each province was added to its allowable gross weight, a tri-
U.S. federal regulations require states to allow a semitrailer at axle semitrailer could be operated freely through the six
least 14.65 m (48 ft) in length, and all states conform to this. provinces at an actual gross weight of 52,000 to 52,500 kg
However, many states also regulate the semitrailer wheelbase, (114,639 to 115,741 lb) without fear of a gross weight offense,
either directly by a measurement from the kingpin to the last so the configuration was harmonized for practical purposes
axle, which is most commonly 13.11 m (43 ft), or by another between the provinces. However, a simple reading of the reg-
measurement. The 13.11-m (43-ft) kingpin-to-rear-axle is not ulations of the provinces did not exactly spell out what could
an issue for 14.65-m (48-ft) semitrailers, or for tandem axle be done.
semitrailers. It may be an issue for a 16.20-m (53-ft) semi- It is clear that significant tolerances can skew outcomes.
trailer with a 3.07-m (121-in.) spread tandem. It is certainly The provinces have agreed there should be no published or
an issue for a Canadian 16.20-m (53-ft) semitrailer with a legislated weight tolerances, and there are now none. They all
3.66-m (144-in.) spread tridem, where a 13.11-m (43-ft) limit retain administrative tolerances that are used at truck inspec-
on kingpin-to-rear-axle forces the tridem bogie forward fur- tion stations at the discretion of enforcement staff in accor-
ther than even the most forward setting allowed in Canada. dance with enforcement policies, to reflect variability in scale
California has a maximum semitrailer wheelbase of 11.58-m equipment.
(38-ft), and Michigan limited the wheelbase of a 16.20-m
(53-ft) semitrailer to 12.34 m (40 ft 6 in.) plus or minus
3.4.7 Winter Weight Allowances
0.15 m (6 in.), so it was simply not possible to configure a
and Spring Weight Restrictions
semitrailer with fixed axles that could operate legally in both
states. Michigan's rule was also much more restrictive than the Some provinces allow additional weight to be carried dur-
Canadian M.o.U. limits. However, it was recently amended, ing a defined period of freeze-up during the winter. Some
and now provides a range of wheelbase that is close to the provinces allow winter weights for all vehicles, while others
Canadian M.o.U., and compatible with California's limit. allow them only for a specific commodity, such as logs, in a
Both overall and secondary, or internal, dimensions need to number of provinces. Winter weight allowances may vary by
be specified to ensure compatibility of vehicles with the high- highway and vehicle configuration and may require a special
way system, and satisfactory low-speed and high-speed dy- permit, depending on the province.
namic performance. The dimensions that need to be specified All provinces impose spring weight restrictions during the
vary with the vehicle configuration. National standards must thaw period that occurs after a real winter. The provinces
address all these dimensions. Experience with state regulation have different and distinct approaches to spring weight re-
of wheelbase suggests that the STAA approach of requiring strictions, and the onset and duration varies widely by loca-
that no state set a dimensional limit more restrictive than the tion, between and within provinces, depending on the sever-
specified value may not be sufficient to achieve the required ity of the freeze-up. Québec applies its spring weight restriction
outcome. It may also require a general stipulation that no state to all highways, even though its main highways may not
can regulate another dimension in a manner that would be require a weight restriction. It takes the point of view that
more restrictive than a nationally specified dimension. if vehicles were allowed at normal weight on main highways,
some of these vehicles would also operate on other roads
where the full weight restriction is necessary, and those roads
3.4.6 Weight Tolerances
would suffer undue damage. Consequently, Québec applies
By the 1990s, the most common tractor-semitrailer in the the same spring weight restriction to all roads. Ontario built
six provinces of eastern Canada was a 3-axle tractor pulling a its primary highway system for full loads all year round. It
