STOPS uses the zone-level demographic estimates for the current year and, optionally, some horizon year to scale the rows and columns of the CTPP 2000 data to estimate travel flows for the year of interest. STOPS uses the zone-to-zone highway travel times to represent travel times for the “drive” alternative in the mode choice model and, in the optional horizon year, to reflect the effects of increasing highway congestion on transit lines that operate in mixed traffic. STOPS uses the zone-to-zone highway distances to compute the change in vehicle-miles of travel caused by diversions of auto travelers to the transit system.
The demographic estimates and highway travel impedances are associated with some set of traffic analysis zones (TAZs) defined by the agency maintaining the regional travel model. STOPS does NOT require that the same TAZ definition be used for the demographic estimates and the highway travel impedances. Similarly, STOPS does NOT require that these TAZ definitions correspond to the small-area definitions used in CTPP 2000 tabulations. Instead, STOPS uses internal GIS-like functions to associate the data across the potentially different small-area definitions used in the various data sources.
In most cases, the source of this information will be the regional travel model maintained by the metropolitan planning organization (MPO) for the area. In some instances, a transit agency may maintain a parallel travel model that represents an alternative source. STOPS users will need to contact the appropriate agency to obtain the information for the current year and, optionally, a horizon year.