CHARLOTTETOWN, P.E.I. – As the size and weight of trucks and truck-trailer combinations has increased over the years, so has the importance of establishing sound weight and dimension regulations.

But a recent review of Saskatchewan’s commercial vehicle permit system says vehicle performance alone is not a good basis for establishing regulations.

The goal – according to authors Cathy Lynn Borbely and Greg Gilks of the Saskatchewan Department of Highways and Transportation, and John Pearson of the Counsel of Deputy Ministers in Ottawa – was to determine how much truck engineering should play a role in setting weight and dimension regulations.

Many of the vehicle weight and dimension regulations in place today were established in the mid-1980s, when expanded and modified limits were placed on weights and dimensions that “directly influence vehicle handling, turning, and stability and control performanc,” they say.

“These targets,” says the study, “are reflected in a number of areas, including resistance to rollover in both turning and evasive maneuvers, braking performance, space required to negotiate turns, front and rear swing-out in turning, and trailer sway.”

There has been a push in recent years, though, for weight and dimension regulations to be based more on what a particular combination can do, performance-wise, rather than simply on its physical characteristics. The Saskatchewan DHT reviewed its permit system for heavy-duty vehicles in 1994 and found there were problems with this approach.

The first problem had to do with the performance criteria itself, which is based on values for things like center of gravity, suspension width and stiffness. “Field enforcement personnel are generally not in a position to evaluate many of these input factors,” the study argues.

The DHT was also concerned, the study says, that performance-based regulations could confuse vehicle owners or actually limit their combination options. On the contrary, the study says, weight and dimension regulations should be designed such that “an owner should be able to look at a trailer in the yard and determine whether it is legal.”

In the end, the study says, the DHT settled for a compromise, using vehicle performance criteria as the basis for standard technical input in the development of easily understood and enforceable regulations.

The problems encountered by the Saskatchewan DHT during this process were good reminders, the authors of the study concluded, “that engineering principles provide good tools for regulatory development, but cannot be taken at face value as the regulations themselves.” n