Excellent article in the Free Press by Brent Bellamy with the broader perspective of how helmet legislation affects cyclist safety for urban commuters and public health.

http://www.winnipegfreepress.com/business/cyclist-safety-in-numbers-not-helmets-384483011.html

Some quotes:

Wearing a helmet when you ride a bike will reduce your risk of injury in an accident. The mandatory helmet law currently proposed by Winnipeg city council likely will not.

This seems like a contradictory statement, but unlike motorcycle-helmet and automobile-seatbelt laws, bike safety relies on a set of unique variables that require a more complex response than simply forcing everyone to wear a helmet.

A 2015 study by the University of British Columbia is the most comprehensive resource for this assertion. It looked at 11 cities in Canada over a five-year period, comparing hospitalization rates between jurisdictions with and without helmet laws. The study was one of the first to pro-rate injuries with the number of bike trips taken. Its conclusions could not find a definitive correlation between helmet legislation and hospitalization rates. …

The effects on participation rates may be the most important factor when considering the effectiveness of legislation and is the reason many cycling advocates oppose mandatory helmet laws.

Although results are inconsistent, many jurisdictions find mandatory helmet use has a negative impact on the number of cyclists on the road.

After implementing helmet laws, several Australian cities reported a drop in cycling rates of between 20 per cent and 40 per cent. Vancouver saw a 30 per cent reduction in adult cyclists, Halifax dropped by 50 per cent and child helmet laws in Alberta resulted in a decrease in adolescent participation by 27 per cent, while adult cycling, which was exempt from the law, grew by 21 per cent.

Almost all research, including the UBC study, concludes one of the most important factors in bike safety is high levels of participation.

It has been consistently proven the number of riders has a far greater impact on bike-injury statistics than wearing a helmet.

This strength-in-numbers concept simply means motorists are less likely to hit cyclists when there are more of them around, indicating doing anything to discourage participation is counterproductive to achieving safety goals. With greater bike presence, drivers become more aware of the complexity of road movements, adjusting behaviour by slowing down, passing cautiously and shoulder-checking. It has been found when bike use doubles in a city the risk of a motorist hitting a cyclist typically goes down by about one-third.

Another significant factor reducing participation rates has been the obsessive public focus on helmet use. The stigma against not wearing one has become wildly disproportionate to the actual risk, creating the common perception cycling in cities such as Winnipeg is inherently unsafe. …