Instead of arguing about how many lives have actually been saved, perhaps a more constructive way forward would be to establish the threshold number of lives saved that would justify the law. And once the threshold has been agreed upon to then establish not the actual number saved, but whether it is plausible that the actual number exceeds the threshold. This is simpler statistical exercise than determining the actual number saved. I would be surprised if a reasonably determined threshold has not been exceeded.

As you may know, a cycle helmet law for children was passed in the Canadian province of Alberta in 2002. Within 6 months, the head injury rate for child cyclists appeared to have doubled:

http://www.vehicularcyclist.com/CalgarySun.htm

Some of that may be an artifact of a change to the system of injury recording. But it is telling that there is no sign that any follow-up work was done to investigate this finding, or to track any benefit from this law. Instead, subsequent monitoring of the effects of the law appears to have focused on measuring compliance only.

One has to wonder whether it is simply assumed that compliance leads to actual improvements in safety, or whether changing the definition of success to compliance is an attempt to deflect attention away from a failed policy.