A discussion of the significant issues involved in developing a model that will help to evaluate alternative transport programs in terms of the changes they may evoke or to justify a program on the basis of reliable forecasts of the values associated with the project. The demand model described, incorporating direct and cross-elasticities, permits both the total amount of tripmaking and the split among modes to be altered as the trip price or travel time for any mode is changed, and treats trip decisions as simultaneous and interrelated. A satisfactory model must also recognize that travel decisions are derived from a large number of socioeconomic factors and that there are a relatively large number of alternatives available to the traveler in terms of purpose, mode, time, route, price, etc. In addition, for forecasting purposes, the model must interrelate demand and price/performance functions and recognize the interaction between the increase in tripmaking as service improves and the buildup of congestion and reduction in service as the volume increases. Lastly, the long-term influence of changes in transportation facilities on social and economic development in an urban area should not be ignored. More intensive effort in data collection in this area is required. 61 pp.