[xxgreg]

He also cites an Australian study, which concludes risk of head injury per million hours travelled: Cyclist 0.41, Pedestrian 0.80, Motor vehicle occupant 0.46, Motorcyclist 7.66.

So if you want to be consistent you should update your comment to:

If you are cycling or driving wear a helmet.

[knowtheory]

Okay, how's this :P

Cars have other safety equipment that make them unlike bicycles. These include airbags, seatbelts, crumple zones and the like.

If you are a driving, you should employ those safety devices when you do so.

[xxgreg]

Ok that leaves pedestrians, who have twice as many head injury's per km. Most likely due to being hit by cars - perhaps cars should have airbags on the outside too...

[Erwin]

Volvo does have such a pedestrian airbag: https://www.youtube.com/watch?v=X2Aw4eZoijk

Apparently that model has scored the highest Euro NCAP crash test as of 2012 (the NCAP tests tests both damage to drive AND pedestrians).