Professor Kenneth Small provided the work trip data that are used in the "Examples" section. These data were collected for the urban travel demand forecasting project, which was carried out by McFadden, Talvitie, and associates (1977). The project was supported by the National Science Foundation, Research Applied to National Needs Program through grants GI-43740 and APR74-20392, and the Alfred P. Sloan Foundation, through grant 74-21-8.