I use a bmx Pro-Tec hard shell helmet, it also provides some protection of the temple area.
Hard shell, smash out helmets will do higher speed impacts...really.
You may still have major neck injury, and unless you wear full face
...(kinda overkill in the city, northshore -yes, you see kids all the time riding to school etc FF, they only own ONE good helmet probably...and it makes them look bada$$.)

and do a face plant, the helmet wont help much.......
.....Unless you are sliding fast on the pavement headfirst toward a curb.

I agree with many of closetbikers points about emphasis being put on firstly a piece of safety equiptment before the road\cycling skills\rules.
But sorry, biking around cars =dangerous, offroad\aggressive sport cycling =helmets both.

I will ride without in the woods on meditative slow rides...on the waterfront.

I know how to fall, drop a bike highspeed, toss a bike from under me offroad.
Chances are in most accidents my head WONT hit the pavement.
I wear it for the accident that totally catches me off-guard, that I have no control of the situation.

The odds are better of surviving with.

Oh.. also, a person that has suffered major head trauma wearing a helmet -DO NOT REMOVE THE HELMET!
The skull may be in pieces, the helmet is now a support for the damaged skull -let the medics deal with it.

Does that sound correct?