There are many factors our traffic engineers look at when making speed limit decisions. Number one is safety. They also look at what the road was designed for, what it is being used for now and into the future. Consistency is also considered so the speed limit does not change several times in a short distance.
There's little evidence that the proposed speed limit reductions will impact travel times. Studies have shown travel time is more dependent on congestion, roadway design and geometry factors than on the posted speed limits. Under medium congestion levels (where traffic is periodically able to travel at or near the speed limit), a lower speed limit may actually reduce overall travel time by allowing a smoother traffic rhythm because lower speeds reduce safe space required between vehicles.
Additionally, unlike in freeway conditions, the average speed for a typical trip is well below the posted speed limits of arterial roadways in the urban road environment. The average speed is more dependent on the nature of stop-and-go traffic as a result of congestion, roadway design and geometry factors than on posted speed limits.
Reduced speed limits will also help to minimize traffic-related fatalities on Lethbridge roads. Higher speeds reduce driver reaction time, increase the stopping distance and contribute to a higher risk of serious injuries and fatalities.