About the authors NORMAN ASHFORD is Professor of Transportation Planning at the Loughborough University of Technology in England. He is a registered Professional Engineer in the United States, Canada, and the United Kingdom. Dr. Ashford lived in North America for 15 years, during which he served as a civil engineering consultant in Canada, did postgraduate work at Georgia Institute of Technology, and began his teaching career at Florida State University. He is a Fellow of the Institution of Civil Engineers and of the Chartered Institute of Transport as well as a member of the American Society of Civil Engineers and of the Association of Professional Engineers of Ontario. He has published many papers and is the coauthor of Transportation Engineering: Planning and Design (1989), Airport Operations (1983), and the author of Mobility and Transport for Elderly and Handicapped Persons (1982). PAUL H. WRIGHT is Professor of Civil Engineering at Georgia Institute of Technology, where he has taught since 1963. He is a registered Professional Engineer in Georgia and a member of many professional societies, including the American Society of Civil Engineers, the Institute of Transportation Engineers (ITE), and the American Society of Engineering Education. Dr. Wright received a Sigma Xi Faculty Award and ITE's Technical Paper Award (Southern Section) in 1976. He has been active in continuing education programs and has served as a consultant to transportation agencies in the United States and Central America. The author of numerous papers, he is coauthor of three other books: Highway Engineering, Fifth Edition (1987), Transportation Engineering: Planning and Design (1989), and Introduction toEngineering (1989). He earned his PhD in civil engineering (transportation planning) from Georgia Tech.