WINNIPEG - Ontario and Quebec now require electronic speed limiters on large trucks, but other provinces are rejecting the concept, saying the devices can sometimes actually make roads less safe.

Even a study commissioned by the federal government has concluded there are safety questions about speed limiters, especially in heavy traffic.

"As the (traffic) volume is set close to capacity ... more vehicle interactions take place and this leads to a reduction in safety especially for those segments with increased merging and lane-change activity, such as on-and off-ramp segments," reads the report prepared last year for Transport Canada by the University of Waterloo.

"In these instances, the introduction of truck speed limiters can actually reduce the level of safety when compared to the non-limiter case."

The study was one of several commissioned by the federal department at a time when Ottawa and the provinces were talking about establishing national rules for truck speed limits.

Ontario and Quebec decided to proceed on their own and now require tractor-trailers to be equipped with engine microchips that prevent vehicles from going faster than 105 kilometres an hour.

The federal studies touted several benefits. Speed limiters would reduce fuel consumption, thereby saving diesel costs and cutting greenhouse gas emissions. Slower trucks would also make for safer roads, such as on four-or six-lane highways when traffic is light or moderate.

But most other provinces balked at the spectre of having slow trucks and fast-moving cars battling for space on crowded freeways or undivided rural highways.

"Most of the traffic already goes well above 110 ... to limit trucks to even less than that and to impede traffic more would probably be a safety problem," says Jerry Bellikka, spokesman for the Alberta Ministry of Transportation.

"If truckers feel that it's going to save them gas or fuel, then by all means go ahead and put (speed limiters) in. But the government is not about to tell people or companies they have to do it."

The Manitoba government considers the federal studies too narrow because they focused on multi-lane freeways and not undivided highways.

"There's a safety issue related to...the ability of one truck to pass another truck safely with speed limiters on a two-lane road," says John Spacek, an assistant deputy minister in Manitoba's Department of Infrastructure and Transportation.

Manitoba is not opposed to the idea of mandatory speed limiters, Spacek says, but it would only adopt such a law if all other provinces agreed - and that's a tall order.

"Most of the provinces, as a far as I know, have said 'no,' other than Ontario and Quebec."

However, supporters of speed limiters stand behind their safety claims, insisting that basic logic dictates that slower speeds save lives.

"They teach you that the first day you go into driver's ed," says Doug Switzer, vice-president of the Ontario Trucking Association, which started the push for mandatory limiters in 2005. "The faster you're going, the less reaction time you have to deal with whatever unforeseen occurrence may happen on the road, whether it be someone cutting in front of you, whether it be a moose running out on the road."

The Ontario government points out that federal studies identified only a potential safety problem and the province remains "confident that reducing maximum truck speeds will improve safety," Transportation ministry spokesman Bob Nichols wrote in an e-mail.

But the issue has divided the trucking industry.

Major trucking companies support the idea and many had limiters installed on their fleets long before the laws in Ontario and Quebec took effect. But many independent truckers are opposed, citing not only safety concerns but also the fact that American truckers are free to travel fast.

Critics say that would put Canadian truckers at a disadvantage when hauling loads through states such as North Dakota, where the speed limit is 120 kilometres an hour on major highways.

Members of the Owner-Operator Independent Drivers Association are planning a convoy to the Ontario legislature March 2 to protest the speed limiter law.