NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

Support for this study was provided by the U.S. Department of Energy (Grant No. DE-FG28-02RW12177), U.S. Department of Transportation (Order No. DTRS56-02-P-70041 and Contract No. DTPH56-05-C-0002), Nuclear Regulatory Commission (Cooperative Agreement No. NRC-02-02-014), Electric Power Research Institute (Cooperative Agreement No. EP-P9056/C4563), National Cooperative Highway Research Program, and the National Academy of Sciences. All opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of these agencies and organizations.

Library of Congress Control Number 200697629

Cover design by Van Nguyen.