Speed Reduction and dangers of Spurious Correlations

Back early in the twentieth century, a study was conducted to determine factors that could have influence on birthrates. Surprisingly, a remarkably close relationship was detected with the number of storks in the community. This proved that, although research findings may be statistically sound, they also can be scientifically humbug. Findings that seemingly explain something but are totally unrelated are called “spurious correlations”. It is important that when a study is presented, it is tested to ensure it is sound. We now turn to Calgary City Hall who relied exclusively on the Neighbourhood Speed Limit Report that was presented to them in November 2020: https://www.calgary.ca/transportation/roads/traffic/traffic-safety-programs/residential-speed-limits.html. It is a worthwhile read before offering an opinion.

The report is entirely based on the premises that casualty rate is directly related to speed and this is supported by various findings in other jurisdictions. However, the study is limited to examining speeds of 50 kmph and below. What happens if data is gathered at higher speeds? Surely the number of deaths rise, would it not? Well, let us see. There is a Dutch report (https://www.rijkswaterstaat.nl/wegen/wegbeheer/onderzoek/verkeersveiligheid-en-ongevallencijfers/actuele-verkeersongevallencijfers/index.aspx) that covers eight (!) years (2012 -2019) of study comparing deaths with speed rates and they found the following:

Speed (kmph):                 15        30        50        60        70        80        90

# of deaths (av./yr.):        1          42        156      87        11        136      1

Thus, using City Hall’s logic, Calgary would be safer and better off by raising the speed limit on residential streets to 70 kmph than by lowering it to 30 kmph, but what does this tell us?

It is evidence that speed is not the only factor to be considered when counting casualties and that measures such as lowering speed must be seen only as a partial solution. Before hurling hundreds of millions of dollars (read: taxpayer funds) on efforts by replacing and installing new signage, City Council must examine what other explanations could be offered that contribute to deadly accidents.

To shed some light on this we refer to the pie graph shown on the Calgary 2018 Traffic Collision Summary Report that mentions the causes of the 40,000 accidents that happen each year on our city streets.  We observe that 35 % of accidents are a result of rear-enders; 21% was because an object was struck; 17% because of sideswipes; 7% because of backing; 7% right angle collisions; 5% left turns and 8% other causes. All the causes have one thing in common: they were all PREVENTABLE. This means that on any given year, Calgarians have on the average up to 40,000 people behind the wheel who do not know how to drive.

To anyone who rides a motorcycle this does not come as a surprise. The number of drivers on Calgary streets who do not change lanes properly, do not shoulder check, do not know how to merge to name a few driving infractions, is absolutely staggering. Not to mention those who are on the phone or use their device for texting or other reasons. Speed, albeit a possible contributor, is not the only reason for accidents to happen and this is totally ignored in the report earlier mentioned.

The root cause is quality of driver education before a person earns an operating licence. That 35% of accidents per year are a result of rear enders means that over 10,000 drivers behind the wheel do not have a clue how to keep proper distance from the vehicle in front of them. This would be an easy target to achieve accident reduction, but this is apparently not on the radar screen. Handing out licences has become a right and not a privilege. On top of that, now the Province in their infinite wisdom allows private examiners testing those who wish to obtain a license. The potential of creating a conflict of interest is enormous because examiners need money and they won’t get that if they fail too many people. Simple as that,

Back in December of 2015, the Mayor and City Councillors were issued each a letter explaining the benefits of traffic circles (or round-abouts). The letter irrefutably presented facts that where round-abouts were implemented, there was a reduction of accident by 35% and a reduction of deadly outcomes by 90%.  No answer was received.

So, here we are. The City Council is about to embark on a gigantic expensive venture to replace signs aiming at lowering the speed limits based on an incomplete report and thereby totally ignoring other factors that arguably have a far greater impact on traffic safety. We therefore suggest putting this (speed lowering initiative) on ice and allow four years to work out a comprehensive plan to address the issue.  In the meantime, it would be advantageous if the city police started patrolling the roads and look for erratic driving behaviour rather than positioning themselves in a strategic position to catch speeders where safety is of hardly any concern but where potential of maximizing revenue is guaranteed.