6. Performing Organization Code:

The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official policy of the Department of Transportation. The metric units reported are those used in common practice by the persons interviewed. They have not been converted to pure SI units because in some cases, the level of precision implied would have been changed. The United Stated Government does not endorse products or manufacturers. Trademarks or manufacturers ’ names appear herein only because they are considered essential to the document. This report does not constitute a standard, specification, or regulation, The publication of this document was sponsored by the U.S. Federal Highway Administration under contract number DTFH61-99-CO0005 awarded to American Trade Initiatives, Inc. Any options, finding, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect those of the U.S. Government, the authors ’ parent institutions, or America