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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.

This study was supported by the U.S. Department of Commerce under contract numbers DG133W06SE5851 and DG133R04CQ0009, the U.S. Environmental Protection Agency under contract number EP06H002306, the Federal Highway Administration under contract number DTFH61-06-P-00121, the National Aeronautics and Space Administration under contract numbers NNS06AE25G and 9724, and the U.S. Department of Homeland Security under contract number HSHQDC-06-P-00161. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the sponsors or any of their sub agencies.

International Standard Book Number-13 978-0-309-12986-2

International Standard Book Number-10 0-309-12986-9

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