SUMMARY: This document supplements NHTSA's August 2005 proposal to upgrade the Federal motor vehicle safety standard on roof crush resistance. We issued that proposal as part of a comprehensive plan for reducing the serious risk of rollover crashes and the risk of death and serious injury in those crashes. In this document@ we ask for public comment on a number of issues that may affect the content of the final rule@ including possible variations in the proposed requirements. We are also announcing the release of the results of various vehicle tests conducted since the proposal and are inviting comments on how the agency should factor this new information into its final rule.