Safety gains related to truck speed limiters come with caveats: Transport Canada study

The introduction of speed limiters for trucks set at 105 km-h increases safety for all geometric highway configurations, especially straight highways, a report for the federal transportation department says.
The basic aim of the study, posted on Transport Canada’s Web site, is to assess the safety implications of mandating speed limiters for large trucks (weight greater than 11,794 kg) for different speeds, including the 105 km-h threshold suggested by recent Ontario and Quebec legislation.
The study is modeled on a stretch of the QEW freeway in the Halton region. It found the “maximum safety gains” of speed limiters “were obtained when the maxium control speed was set to 90 km-h for uncongested traffic volumes.”
Safety gains were also realized at 105 km-h, but as control speeds increased, the safety gains decreased, the report notes.
“As maximum speed is set to 110 km-h, the safety gains with the introduction of mandatory limiters become less prominent,” the report says.
Safety gains also decreased as the volume and percentage of trucks on the road increased.
“As the volume is set close to capacity (200 vehicles per hour per lane), more vehicle interactions take place and this leads to a reduction in safety, especially for those segments with increased merging and lane-changing activity, such as on and off ramp segments,” the report notes. “In these instances, the introduction of truck speed limiters can actually reduce the level of safety when compared to the non limiter case.”
The report also notes more research needs to be done on the use of speed limiters when trucks are driving on rural, two-lane highways.
“The implementation of mandatory speed limiters on rural, two-lane highways may lead to an increase of passing manouevres onto the opposing traffic lane,” the report says. “The possibility for increased unsafe passing manouevres poses special safety challenges where trucks are set by limiters for two-lane undivided rural highways.”