A method of coding generalised cost transit system access links is described, and the advantages of using large zones in transportation planning are demonstrated. Use of large zones is motivated by the expense (in time and money) of making travel demand forecasts. The method was developed concurrently with the models for predicting the values of the access link times for rail and bus trips. These supply models estimate the in-vehicle times on automobile and bus and the out-of-vehicle times for bus and rail access links using zonal and modal characteristics. Use of different zone sizes is evaluated by a correlation analysis between the predicted and the actual number of rail riders. The results indicate that there is a high correlation between the predicted and actual number of users; the error increases with the zone size, but the increase is small. Error sources independent of zone size also exist; these errors are discussed in detail. It appears that large zone sizes can profitably be used in transportation planning. The access supply models used are very simple. A more complex set of models has been developed. The reason for reporting this simple model is validation. Data collected in extant transportation studies focus on the demand side and made the validation of supply side models impossible. In the present study the data are rich enough but date back to the late 1960s. Good methods are timeless, however.
Abstract