Trailers that transport the payload (without pounding the pavement)

Jan. 1, 2004
THE SEARCH is on in Ontario for trailers with SPIF. is an acronym for trailers that are Safe, Productive, and Infrastructure Friendly. The Ministry of

THE SEARCH is on in Ontario for trailers with SPIF.

“SPIF” is an acronym for trailers that are “Safe, Productive, and Infrastructure Friendly.” The Ministry of Ontario is in the process of identifying tractor and trailer configurations that allow the trucking industry to do just that — operate safely and efficiently while minimizing wear and tear on the highways in the province.

Ron Madill, a senior policy analyst with the Ontario Ministry of Transportation, shared some of the results of research in a presentation to the 40th annual convention of the Canadian Transportation Equipment Association in Surrey, British Columbia, November 4.

He focused specifically on the latest phase of the project. Two earlier phases already have been completed as Ontario looks to reform its vehicle weight and dimension regulations.

“Ontario allows heavy axles and gross weights,” Madill said. “We allow unlimited number of axles, including lift axles. The resulting vehicles are very productive. But we have safety concerns and excessive road and bridge damage. Our purpose is to identify vehicles that are safe, productive, and infrastructure friendly. We want to cause a migration of SPIF vehicles while at the same time deal fairly with existing vehicles.”

Madill said he looks at Ontario's size and weight regulations as a three-legged stool. Because of the large payloads the province allows, the “productivity” leg of the stool is strong. The “safety” leg is a little wobbly.

“The infrastructure leg is about to fall out,” he said. “From a policy standpoint, we need to find balance. We are concerned about all three of these areas.”

In the past, the ministry has talked about infrastructure-friendly vehicles. The term “SPIF” (which includes safety and productivity) has been used recently in order to stress the balance the ministry is attempting to achieve between these three conflicting interests.

Madill said the variety of configurations of trucks and trailers would be overwhelming if the ministry tried to address every type simultaneously. Some common configurations already have been addressed, including dump trailers and three-axle trailers that do not dump. Madill concentrated his presentation on Phase 3 of the project, which includes non-dumping semitrailers with four or more axles and all doubles trailers.

“We already have in place a SPIF four-axle vehicle (a self-steering quad),” he said. “We still need SPIF alternatives for semitrailers with five or more axles, along with A-, B- and C-train doubles.”

As part of the project, the National Research Council of Canada was hired to assess state of self-steer axle technology, identify SPIF candidates to replace 5+ axles, undertake computer simulations, and propose any necessary full-scale tests. Purpose of the tests would be to validate simulations and to address performance issues.

Self-steer axles

Included in the research was a look at the performance of self-steering trailer axles.

“These axles have been used successfully for many years in a relatively narrow range of operations,” Madill said.

Research indicated that the use of self-steering axles is branching out into other, more conventional applications. Part of the reason is improvements in axle performance. Manufacturers have upgraded the product, and operators have learned more about how to use them successfully.

“Drivers generally are happy with the handling of trailers equipped with self-steering axles,” Madill said.

Viable candidates

SPIF trailers that are candidates for replacing current tractor-semitrailer configurations are equipped with five or more axles. Four semitrailer alternatives were identified — two equipped with five axles and two with six axles. One trailer had two lift axles ahead of a tridem. The other had one self-steer axle on either side of the tridem.

In addition, three four-axle tractor configurations were identified:

  • A tri-drive tractor
  • A tandem with self-steer pusher
  • A twin-steer.

Each of the configurations under-went computer simulation testing. Tests included:

  • Static rollover threshold (SRT)
  • High-speed offtracking (HSOT)
  • Load transfer ratio (LTR)
  • Transient high-speed offtracking (TOT)
  • Low-speed offtracking (LSOT)
  • Rear outswing (RO)
  • Friction demand in tight turn (FD)
  • Lateral friction utilization (LFU).

And the winner is…

Based on the result of the computer testing, the tri-drive tractor in combination with the self-steering quad trailer provided the best results among the vehicles tested.

“The tri-drive tractor already is in extensive use here in British Columbia and Alberta,” Madill said.

Other tractor configurations — the self-steer pusher and the tandem-tandem — were not as well received.

“There were some issues identified in the computer simulations, but we have not necessarily rejected those vehicles,” Madill said. “The issues that were identified were outside the scope of this phase of the project. We probably will look at them in subsequent phases.”

Performance of the two five-axle trailers was sufficient to merit further study. The tri-drive tractor and self-steering quad trailer tested well — if the dimensions and weights are carefully controlled. The primary concern with a tri-drive tractor is possible difficulties with steering, the result of drive axles trying to push the tractor through a turn.

Factors affecting steering of a tri-drive tractor include how the tridem is spaced, the wheelbase of the tractor, and the amount of weight on the front axle. A rule of thumb is that the front axle must carry at least 27% of the tridem weight. The wheelbase should be at least 6.6 meters (260 inches).

The two six-axle trailers had a number of performance and infrastructure issues, Madill said, and have been eliminated from consideration. Furthermore, the additional axle seems to provide little if any benefit. Madill called the sixth axle “redundant.”

More to be done

The report, now available in the public domain, recommends that full-scale testing be performed. The full-scale testing is intended to validate the computer simulation and to address some of the concerns that have been raised about some of the configurations.

The ministry plans to issue a discussion paper for the review of interested parties, including carriers, shippers, and various safety organizations. Simultaneously, the ministry will conduct full-scale testing. Testing is expected to include low-speed right turns to assess friction demand, high-speed offtracking, high-speed lane changes at 0.15 and 0.30g, forced steer of self-steer axles, and vehicle response to speed bumps.

Results are expected in mid-2004.