Why it makes sense to bike without a helmet — Howie Chong : Howie Chong

Over half of all head injuries occur in motor vehicles and more people were hospitalized after walking down the street than riding on a bicycle. Consider another statistic: According to a 2006 French study, pedestrians are 1.4 times more likely to receive a traumatic brain injury than unhelmeted cyclists. We can also approach it from the perspective of injuries per million hours from a 1996 Australian study looking at head injury risk before the beginning of any helmet laws:

Risk of head injury per million hours travelled

Cyclist – 0.41

Pedestrian – 0.80

Motor vehicle occupant – 0.46

Motorcyclist – 7.66