Helmet Laws and Tiered Licensing?

It might be the case that having helmetless riders is a net gain to the economy. I remember seeing a study by some economists that concluded that smoking saves money for taxpayers, because fewer people make it to old age, which are the expensive years for taxpayers in terms of medical care. I don't have a clue whether the same would be true of helmetless riders or not, but it wouldn't surprise me. The bigger issue is that in order to utilize the " burden to taxpayer" argument, the number of factors to be considered to come up with the real costs is actually pretty staggering, and I am not willing to just assume that the result would favor helmet laws. Anybody seen any good studies?