In the 1960s, U.S. and Canadian rules on weights and dimensions were almost identical. But things didn’t stay that way for long. By the time the 1980s came about, fleets could not legally run a single vehicle combination across the country.
With the patchwork of vehicle weights and dimensions seemingly out of control, a study proposed in 1981 would eventually establish key engineering standards — determining if various configurations were safe, and measuring their effects on pavement.
The three-year, $2.8-million study became the largest cooperative research program ever undertaken in Canada. Two years of analysis followed, leading to the first national Memorandum of Understanding in 1988.
For the first time there was hard data to consider safety and infrastructure rather than just increasing demands for greater productivity.
As subsequent testing later proved, those interests are not mutually exclusive. Canada now has among the most productive truck configurations anywhere on the planet — and one of the best overall safety records.
The impact of nationally harmonized weights and dimensions has been huge. Studies identified $3.85 billion in efficiency-related savings between 1988 and 2002. Truck traffic exposure dropped by 135 million vehicle-kilometers.
And those gains came with no increase in observed pavement and bridge costs.
Where and what was tested
Before the engineering and research, Roads and Transportation Association of Canada (RTAC) and National Research Council (NRC) representatives fanned across the country in June 1984, gathering details about common truck configurations. They looked at the kinds of components typically used, such as tires, brakes and suspensions, as well as how they are configured with things like fifth wheel positions.
The two-year test phase evaluated 13 different heavy-vehicle configurations. Engineers ran basic computer simulations, later validated in real driving scenarios. The simulation work was conducted at The University of Michigan Transportation Research Institute (UMTRI), while the driving tests were completed at the Ontario Ministry of Transportation and Communications facility in Centralia, Ont.
A tilt table was installed at the Centre de Recherche Industrielle du Quebec (CRIQ) in Blainville, Que. There, a truck could be positioned on the platform while one side was raised to simulate a rollover. Using data generated by UMTRI’s computer simulations, tilt angles were linked to the amount of lateral acceleration a vehicle could sustain in a curve.
UMTRI’s computer simulations let engineers change viewing angles. Yaw, roll curvature, and weight distribution could all be plotted.
Engineers working on a former airfield runway at Centralia tested braking, steering, and suspension loads on high- and low-friction surfaces, straightaways, and curves.
Meanwhile, the impact of up to 16 different truck axle loadings and spacings were tested at 14 pavement testing sites across the country. An old 45-foot flatdeck trailer was fitted with six liftable air-suspension axles. Each wheel end was fitted with identical tires, as was the tractor. The trailer, loaded with 27 1,000-kg concrete blocks, and weighing 105,000 pounds, was towed to the various test sites.
Patches of highway were fitted with sensors to measure pavement compression and rebound. Dozens of runs were made with several axle configurations. The driver of the test truck, Jim Kelly, had to keep all the wheels within one inch of the sensors on every pass.
“He called the job the most boring, nerve-wracking experience of his life, and swore he’d never do it again, not for any money you’d care to pay him,” project manager John Pearson wrote in a Canroad Transportation Research newsletter.
On top of that work, a 10,500-gallon compartmentalized tank body was fitted to a specially designed chassis to evaluate the load-sharing capabilities of generic walking beam, air, spring, and rubber suspensions.
What the tests revealed
With a few exceptions, all that testing didn’t reveal any right or wrong answers. But it did show that some configurations performed better than others in certain ways. For example, the pavement testing revealed a tridem axle group had the least damaging impact on pavement as axle weights were increased. Testing revealed that if you increase the weight of a single axle by 10%, the increase in pavement damage can be up to 30% because of the relationship between the load and the pavement response.
“The research showed multiple axle groups such as tandems or tridems actually provide stress relief in the pavement,” says Pearson, now the secretary of the Council of Deputy Ministers Responsible for Transportation and Highway Safety. “You can increase the weight on the tandem or tridem without the same dramatic increase in damage.”
This helped gain acceptance for tridem axles in Western Canada, where pavement tends to be thinner and more flexible.
Testing also revealed certain combinations such as short- to medium-length, 7-and 8-axle A-train doubles had undesirable dynamic characteristics, while the 8-axle B-train had excellent dynamic performance.
In terms of dynamic performance, the testing also revealed the impact of additional articulation points, axle numbers, axle spreads, and wheelbases.
Longer wheelbase vehicles had better high-speed off-tracking performance (curves at highway speeds), but did worse than shorter vehicles in low-speed off-tracking (turning corners on city streets). On the other hand, increasing axle spreads improved low-speed off-tracking performance but had a negative impact on high-speed off-tracking.
“I think the most fundamental achievement of all that research was it helped us answer the age-old question: Is it safe.” Pearson says.
Crafting the first MoU, 1988
Limits are established by provincial and territorial engineers and analysts. But it’s ultimately politicians, who can be swayed by lobbyists and activists, to greenlight such recommendations. The truckload of data helped to back decisions that were formally educated guesses.
The research continues to influence decision making to this day.
For example, when B-train doubles were shown to have better dynamic performance than A-train doubles, weight restrictions were imposed on the A-train, giving the B-trains a market advantage. With that weight advantage, B-trains immediately became the configuration of choice for heavy loads in the four western provinces.
These weight limits still allowed the use of the familiar five-axle A-train combinations commonly used by LTL carriers.
Similarly, the box lengths of A- and C-train doubles was limited to 18.5 meters (60 ft 8 in.), while the B-train double was allowed 20 meters (65 ft 7 in.). This encouraged seven-axle B-trains for light- and moderate-density freight.
Those are but a few examples of how the research-generated data went on to influence commercial vehicle configurations.
In the mid- to late-1980s, the goal was to establish a roster of vehicles that could move freely about the country on designated highways.
A committee developed detailed specifications for tractor-semi-trailers with three to six axles, and A-, B-, and C-trains from five to eight axles. These specifications formed part of a Memorandum of Understanding Respecting Heavy Vehicle Weights and Dimensions.
Under the MOU, each province retains the right to allow higher weight limits or different configurations for truck operating within its boundaries.
Trouble on the horizon
The original 1988 MOU defined weight and dimension limits for tractor-semitrailers and A-, B-and C-train double combinations with the following limits:
- single axle load: 9,100 kg (20,061 lb.)
- tandem axle load: 17,000 kg (37,478 lb.)
- tridem axle load 2.44 m (96 in.) spread: 21,000 kg (46,296 lb.)
- tridem axle load 3.05 m (120 in.) spread: 23,000 kg (50,705 lb.)
- tridem axle load 3.66 m (144 in.) spread: 24,000 kg (52,910 lb.)
Those axle loads represented increases for the four western provinces at the time, but were generally consistent with or less than weights allowed in the six eastern provinces. There was essentially no effect on single and tandem semitrailers, while the tridem semitrailer introduced a configuration with an intermediate weight capacity.
In terms of dimensions, the MOU permitted 53-foot trailers. The testing proved they would fit into the envelope if inter-vehicle dimensions and axle-group spacing was maintained. Such trailers were not used in Canada at the time (1988), but were gaining traction in the U.S. and were expected to supersede 48-foot trailers.
The provinces took different approaches to adopting the MOU. British Columbia, Alberta, Saskatchewan, and Manitoba adopted it as their size and weight regulation, while grandfathering existing noncompliant configurations at their existing weights. These provinces implemented the MOU in 1989 with the semitrailer and overall length at the originally agreed lengths of 16.2 m (53 feet) and 25 m (82 feet).
Ontario adjusted its rules in 1989 to allow most MOU configurations, but public opposition to the longer trucks forced politicians to cap the overall length for tractor-semitrailer combinations at 23 meters (75 ft 6 in.), which limited trailer length to 14.65 meters (48 feet). With 53-foot trailers seen as inevitable across North America, Ontario fleets unable to upgrade to the longer wagons canceled orders for 48-foot trailers, forcing the closure of several domestic trailer manufacturers.
With Ontario refusing to comply, the MOU languished in Quebec and Atlantic Canada as well.
The same year that saw the first national MOU signed by all Canadian jurisdictions saw the Canada-U.S. Free Trade Agreement – a harbinger of changing trade patterns that would shift from east-west to north-south. As trade with the U.S. increased, and with 53-foot trailers becoming the trailer of record in the U.S., Ontario found itself unable to turn the tide of loaded 53-foot trailers arriving at its southern borders.
The cost and inconvenience of having to trans-ship freight destined for Canada via Ontario was enormous. A study conducted for Ontario Ministry of Transportation (MTO) revealed it cost the province about $100 million annually in additional transportation costs.
Ontario eventually began issuing permits for 53-foot trailers, and in July 1994 finally amended its regulations to allow 53-foot trailers with an overall length of 25 m (82 feet).
Beyond the 1988 MOU
The MOU has seen 10 amendments up the most recent effort, signed in January 2019. It is updated as new technology develops or the need for additional configurations arises — or as existing configurations improve.
We’ve been at this harmonization thing for more than three decades and we’re not even close to a fully compatible set of weights and dimension regulations – and probably never will be. That’s not a bad thing. The rules in each jurisdiction reflect local market conditions that may not even apply to an adjacent province, never mind a province on the opposite side of the country.
There are regional agreements that allow certain configurations to travel across several provinces, such as the four western provinces or the Atlantic provinces. There’s also crossover that allows some configurations to operate between two provinces or regions.
As challenging as the Canadian confederation can be, we seem to find ways of making it work, as a National Academies Press report shows.
Ontario’s SPIF (Safe, Productive and Infrastructure Friendly) configurations are great example of the engineering horsepower that can be brought to bear on a tough challenge. As unwieldly and confusing as they are, they permit maximum productivity at minimum cost to infrastructure.
But with harmonization as great as it’s ever been, the need for inter-provincial compatibility is almost non-existent. Recent statistics from MTO show that only about 3% of the trucks leaving Ontario cross the Manitoba border. And with all the effort put into increasing allowable weight limits, freight density is half of what it used to be.
“Everything is palletized now,” Pearson observes. “Only a fraction of trucks is running at or close to the weight limit, and that’s mostly bulk carriers and steel haulers that are designed to operate at maximum gross vehicle weight.”
And in recent years, we’ve seen a lot of technology introduced to heavy trucks, such as electronic stability control and smart lift axles that can manage some of the issues identified in the 40-year-old truck weights and dimensions study.
I have had the good fortune to attend many Council of Ministers Responsible for Transportation and Highway Safety Weights and Dimensions subcommittee meetings. Certain issues hit the agenda, remain there for a few years, and then disappear as they are resolved.
Presentations on wide base single tires were staples of those meetings for years. Sessions on 6×2 tractors were common for a few years but have faded away. Smart lift axles are still a hot topic. And every now and then someone invents something new and comes to the meeting to make a presentation.
It’s because of people with new ideas, combined with market forces and political will, coupled with reliable testing and evaluation methods that Canada has made such great strides in truck productivity. Unlike the U.S. — where practically nothing has changed in 40 years — Canada continues to improve efficiency and lower emissions.
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