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allows travel at legal weights on these highways during the modified semitrailers would be equivalent to a newly manu-
thaw period, but applies a standardized axle weight limit to factured semitrailer, the regulation required the company
secondary highways and other roads. Other provinces, such doing the work to affix its own compliance label beside that
as Alberta and Saskatchewan, may apply a specific weight of the original manufacturer, with the new gross vehicle
restriction to axle groups, or to gross weight for a specific weight rating and gross axle weight ratings. Thus, only a man-
highway. ufacturer registered with Transport Canada as qualified to
By the early 1980s, after a couple of rounds of response by manufacture and modify, a semitrailer in this case, with air
other provinces to Ontario's change in 1970, the preferred ve- brakes would be allowed to do the work. The manufacturer
hicle in the Prairie Provinces from the regulations would have was therefore required to certify that the modified semitrailer
been a 7-axle B-train. However, when spring weight restric- would meet the pertinent safety standards at the time the
tions were considered, an 8-axle A-train was the most pro- vehicle was modified.
ductive on a year-round basis, so this was the configuration
of choice for heavy haul. The A-train rear trailer is prone to
3.4.9 The Scientific Approach
roll over in an evasive maneuver, and repairing damaged pup
trailers was a good business for trailer manufacturers. The CCMTA/RTAC Vehicle Weights and Dimensions
Winter weight allowances and spring weight restrictions Study produced a set of principles for the configuration of ve-
mean that the configuration that can move the greatest hicles (18), based on a procedure for evaluating the dynamic
weight of a particular commodity in a particular part of a par- performance of vehicles. The procedure is straightforward:
ticular province over a whole year is not necessarily the con-
figuration that has the highest allowable gross weight in the 1. The vehicle makes a standard maneuver under specified
summer. The actual outcome is not necessarily the obvious conditions;
outcome from a simple reading of the rules, and the outcome 2. Performance measures are computed from the responses
may differ depending on how a jurisdiction imposes the to this maneuver; and
weight allowance or restriction. 3. Each performance measure is compared to a correspond-
Winter weight allowances and spring weight restrictions all ing performance standard, to determine whether per-
result in differences from the standard legal weights, which formance is satisfactory or not.
generally serve as the basis for most evaluations of vehicles,
and evaluations of their impacts on roads and bridges. There CCMTA/RTAC Vehicle Weights and Dimensions
Study used seven performance measures (18) that related to the
dynamic performance of semitrailers. The seven original per-
3.4.8 Vehicle Modifications
formance measures are also more broadly applicable to other
When the truck size and weight regulations change, carri- vehicle configurations. However, some vehicle configurations
ers may have to buy new vehicles, or they may be able to mod- have critical performance measures that were not included in
ify an existing vehicle to the proper configuration. A new ve- the original seven, and new performance measures have been
hicle should meet all pertinent safety standards at the time of developed to address the characteristics of these vehicles. The
manufacture so that is not a problem later. Suppose a vehicle original seven performance measures, and others developed
is being modified to have a higher gross vehicle weight rating since, are outlined in Appendix D, with commentary.
than it was built with. The gross axle weight ratings of the ex- After the M.o.U. was put in place in 1989, each province also
isting axles may not be sufficient for the new vehicle. The had a range of other configurations, principally truck-trailer
structure may need to be reinforced for higher payload combinations. Collectively, the provinces asked, now that
weights. The brake system may be modified and may not tractor-semitrailers and doubles had been configured to ensure
comply with the current timing requirements of FMVSS 121, they met objective standards for dynamic performance, should
and so on. There are many things that might need to be mod- other configurations also be treated in a similar manner? The
ified so that the vehicle would be equivalent to a newly man- same procedure for evaluating the dynamic performance of ve-
ufactured vehicle. Not all owners might want to spend the hicle was therefore used to add straight trucks and truck-trailer
amount of money on a vehicle to ensure the job would be combinations to the M.o.U. in 1991 (40), for Québec to elim-
done properly. Not all entities that might undertake the work inate Ontario multi-axle semitrailers in favor of the self-steer
would necessarily understand, or be able to do, all that would quad semitrailer (45) also in 1991, and subsequently for the
be required. forestry industry in British Columbia and Alberta to work with
When Ontario introduced self-steer tri-axle and self-steer the provincial governments to identify preferred configura-
quad semitrailers in 2001, theses could readily be modified tions for legal and permit operations at the highest allowable
from existing tri-axle or quad semitrailers. To ensure that gross weights (50). All provinces have used the same process
