Studies by the National Highway Traffic Safety Administration (NHSTA) determined that making all autos 100 pounds lighter would kill an extra 400–1,300 Americans per year. However, these studies made the error of conflating weight with size. For automotive crash safety, the determining factor is size, not weight: larger vehicles have more crush space to absorb impacts. Peer-reviewed reanalysis of NHSTA's data showed just the opposite was true: decoupling weight from size improved safety. Making all autos 100 pounds lighter would actually save 1,500 lives a year.
Van Auken, R.M. and J.W. Zellner. January, 2003. “A Further Assessment of the Effects of Vehicle Weight and Size Parameters on Fatality Risk in Model Year 1985–98 Passenger Cars and 1985–97 Light Trucks.” Torrance: Dynamic Research, Inc.