Not to mention what must be a vastly larger number of head injuries while inside of motor vehicles.

(Ever hear of someone suggesting a helmet law for cars? Maybe those bike helmet law proponents really do have something else in mind besides safety.)

Close, but not quite, Andy. The vast majority of bike-related injuries result from falls that do not involve autos. Indeed, helmets are much more effective in these mundane, low-speed falls than they are in collisions with faster moving vehicles, in which helmets offer only limited protection.

Yet, even that misses the larger point. While individuals are clearly better off wearing than not wearing helmets, society benefits from more bicycling, period, helmeted or not. Then, safety-in-numbers kicks in, as you saw in Davis. So, as a matter of public policy, governments should take a laissez faire approach to helmet regulation.

Credit cards seem like a good idea but this is probably unfairly biased against those without credit cards.

One thing that might work is to use bicycles for commuter rail riders who do not want to switch the subway. There have been proposals to extend the commuter railroads to Lower Manhattan, but these are inconceivably expensive. The subway ride from Grand Central or Atlantic Ave is unpleasant because the subways are already jammed before the suburbanites get on.

LIRR and MetroNorth could loan bikes, helmets, and (if needed) raingear to their monthly riders who live beyond a walk from the terminal. The alternative, now that I'm thinking more broadly about bikes -- like walking, but three-plus times the distance in the same time -- is for riders to bring folding bikes on the train. But lending bikes would be easier and not congest the train. And it would be cheaper than a new tunnel from Altantic Terminal to Lower Manhattan.

I'm not a big fan of bike share here in our archipelago, either. I don't think NYC has enough dedicated cycling lanes and tracks to make it a reasonable option (getting from Union Square to Essex & Delancey, for instance, in less time than a cab) for anyone who is not already a skilled city cyclist. Paris has tons of bike and bike/bus lanes for Velibistes to use to get around.

The solution is simple. A rider could be required to wear his or her own helmet in an NYC bike-share program. Get caught not wearing one while riding and you get a warning. Do it again, your barred from the system.

Admittedly this might be difficult with tourists.

A note about helmet use: When I was out in Davis CA for the big APBP conference in September, bike helmets were considered optional for adults. It was (dare I say) even socially acceptable by those in authority. Davis has done such a good job of making their streets safe for cyclists they don't worry so much about helmets anymore. Don't forget the real cause of head injury while on a bike is from getting hit by a car. Admittedly, Davis is just a little college town and NYC is much much bigger, nastier beast to tame.

There is a gap of the imagination where people who use a bike to get around see it as no big deal and people who don't will say things like, "I can't bike to work - it's almost 60 blocks", or "I'll be covered in sweat if I bike to work".

This is not to bash Bloomberg, but just to maybe wonder how that gap in imagination can be bridged.

I was there for 2 months in April-May 2007, and it had just opened with 200 bikes and 14 stations. As of July 1, 2007, they were up to 1500 bikes and 100 stations.