The defining demographic characteristics of almost all aspects of North American society post-World War 2 have been the tremendous growth in population and the movement of the "baby-boom generation" through the aging process.This huge increase in population resulted in demands for housing, employment, and government services.Rising household incomes created a market demand for personal transportation that was satisfied in the majority of cases by the automobile.Although most pronounced in the United States, a similar population "bump" occurred in Canada (the population surge occurred later than in the United States).The growth in population over the past 40 years has been accompanied by changes in other factors important to transportation planning and critical in explaining corresponding increases in urban travel