Date: August 27, 2010
From a practial point of view, is there justification in having seat belt laws? In order to answer this question, we need to answer some other questions.
Regarding money we can ask, "What are the possible ways that seat belt laws can save money?"
Sam Peltzman wrote a paper titled The Effects of Automobile Safety Regulation, The Journal of Political Economy 1975, 83(4), pp. 677-726. The ideas of the paper have come to be known as the Peltzman Effect.
The Peltzman effect is the hypothesized tendency of people to react to a safety regulation by increasing other risky behavior, offsetting some or all of the benefit of the regulation.
An interview with Peltzman can be heard (or read) at the Library of Economics and Liberty.
Alma Cohen and Liran Einav have both written a paper titled The Effect of Manditory Seat Belt Laws on Driving Behavior and Traffic Fatalities. The paper was written Novermber 2001. It was published in the Review of Economics and Statistics, Vol. 85, pp. 828-843, 2003. You can read the paper at the Social Science Research Network. As of August 27, 2010, the paper was free to read and download without registration. It addresses Peltzman throughout the paper.