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opinion

Murtaza Haider is a professor of management at Ryerson University. He is currently working on a book on data science and analytics, which will be available in October, 2015.

If Ralph Nader were to opine on lowering speed limits in Toronto, he might argue it's "unsafe at any speed."

In 1965, Mr. Nader in his book, Unsafe at Any Speed, challenged the auto industry's reluctance to introduce seatbelts that would improve the safety of drivers in collisions.

The decision to lower the speed limits on residential streets by the Toronto-East York Community Council (TEYCC) has reopened the age-old question: safe at what speed? The proponents cite research showing pedestrian and bicyclist safety improves at lower speeds. The detractors believe slower speeds may aggravate drivers even further, thus worsening safety for pedestrians and cyclists. In this argument, both sides are correct, at least partially.

Research in traffic safety confirms that collisions between pedestrians (or bicyclists) and automobiles are less fatal at lower speeds. In effect, most pedestrians will survive if hit by a car traveling at 30 km/hr. At 50 km/hr, pedestrians face an 80 per cent risk of being killed in a collision.

It is hard to argue against the notion that the pedestrian and bicyclist safety is higher at lower vehicle speeds. At the same time, it is naive to assume that a blanket reduction in speed limits will automatically be greeted with compliance. Research also shows that when speed limits are arbitrarily set lower than the design speeds for road segments, drivers do not find those limits credible, resulting in less conformity than desired.

The key point to realize is that the geometric design of road segments is based on, among other factors, the intended operating speeds of vehicles. The lane widths, the layout of curves, and stopping sight distances are designed with specific operating speeds in mind. The odds of a collision or an incident increases when drivers operate vehicles at speeds higher than the design speed. The same is true when speed limits are set lower than the design speeds. When the posted speed limits are arbitrarily set lower than the design speeds, some drivers will drive (not necessarily intentionally) at speeds higher than the posted limit. The odds of rear-end collisions will consequently increase, though pedestrian safety will not fundamentally improve.

Many proponents of lowering speed limits cite European examples. They, however, fail to recognize that the residential streets in older parts of European cities were designed in the pre-car era to facilitate commuting by horse-driven carriages. The lower speed limits in such cases conform to the original design speeds.

The frequency of fatal collisions during 2009 and 2013 in the TEYCC districts suggests little room for improving safety performance. A report by the Toronto City staff revealed that a mere 6.8 per cent of fatal pedestrian and 0 per cent of fatal cyclist collisions took place on local roads earmarked for lower speed limits. Most fatal collisions occurred on arterial roads that will not experience any change in speed limits.

At the same time, many residents feel disenfranchised for having no control over the streets in their neighbourhoods. They believe noisy through traffic threatens the safety of their children and limits their ability to enjoy their communities.

At the same time, the proponents may have ignored an unintended consequence of a 30 km/hr speed limit – an increase in travel times for school and transit buses using local roads. This may require parents to have their children leave for school sooner.

A compromise is possible that may result in better driver compliance. Instead of blanket speed limits, all design speeds should be reviewed and limits should be aligned with the road's original design specifications.

In instances where the residents demand speed limits below the design speeds, a mere posting of lower speed limits will not necessarily deliver the desired outcomes. Traffic calming interventions, such as speed humps and curb extensions, must also be considered. .

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