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III. DEVELOPMENT OF TRAVEL FORECASTING MODEL <br /> The Thoroughfare Planning Unit (TPU) of NCDOT <br /> the DCHC Urban Area transportation planning provides technical assistance to <br /> travel forecasting model for the study area. eThist model is as d upon parbattery <br /> of mainframe computer procedures made available by the Federal Highwa Ad - <br /> tration. A brief description of how this model operates follows. Y minis- <br /> Methodology <br /> The travel forecasting model is comprised of three major parts; trip generation, <br /> trip distribution, and trip assignment. <br /> Trip Generation <br /> Three categories of trips are used: <br /> (1) Interim-Intern l Trips are those in which both ends of the vehicle trip <br /> occur within -the study area. Trips are described in terms of Produc- <br /> tions and Attractions. Trip Productions <br /> produced are a <br /> function of the number and type of dwelling units nbea hsofethe area's <br /> 600 analysis zones. Housing is stratified into five categories of <br /> standard (single-family and multi-family) dwellings which have trip- <br /> generating propensities from 6.0 to 12.0 vehicle trips <br /> sixth category for group A per day (VPD). A <br /> sixth uses 1.4 for group quarters (e.g, college dormitories and boarding <br /> per unit (defined as each individual). These trips <br /> are divided into three purposes; Home-based work (HBW - 27 , Other <br /> ' <br /> home-based (OHB - 49t), and Non-home based VHB ) <br /> number of secondary NHB trips produced by non-residents are added tto <br /> the NHB Trip Productions, Trip Attractions for each internal trip <br /> purpose are based on each zone's relative "attractiveness" which is <br /> calculated as a function of its number and type of employment. As a <br /> result, each zone has estimated numbers of trips produced and attracted <br /> for each of three internal trip purposes, <br /> • <br /> (2) External internal Trips are those in which one end of the vehicle trip <br /> occurs outside the study area. These can be either b or <br /> non-residents. The trips are considered to be by residents <br /> produced area's <br /> external cordon stations and attracted to the internal analys analysis zones <br /> based its employment (non-residents) and housing (residents). <br /> (3) External-maternal (Through) Trips are those which are both produced d <br /> attracted by the external stations. These trips do not stop within ain <br /> the study area. The total traffic at any station <br /> through trips with the rest being external-internal.anel from Oo to 65% <br /> 3.1 <br />