Agenda - 02-16-1988 - Laserfiche WebLink

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III. TRAVEL FORECASTING METHODOLOGY An important aid in developing a good thoroughfare plan is a set of carefully developed travel forecasting models which provide reliable traffic data for consideration while analyzing, various roadway system scenarios. The models for this study are the largest and most complex ever developed in North Carolina. The first step in developing travel forecasting models is to define a study area and to partition it into smaller districts which are further divided into individual into traffic. analysis zones within which land uses are relatively homogeneous (e.g., containing only commercial uses or only residential uses, as much as practicable). Due to modelling idiosyncrasies (specifically that each zone can have a maximum of four connection points to the computer simulation network), zone boundaries are also defined such that each zone's traffic impacts are isolated to as few roads as possible. In the DCHC Study, the planning area is comprised of 600 internal zones and 45 external cordon stations (representing roadways at the study boundary). The next step is the collection of housing and employment data. Data collectors surveyed residential areas and classified them as to their propensity to produce auto-driver trips (i.e., above average size dwelling units, with more residents who drive automobiles, tend to produce more trips than below average dwelling units). The collectors surveyed businesses as to number of employees (present and projected). Businesses were also assigned trip attraction rates. These rates were assigned via of a coding system developed on a nationwide basis (Standard Industrial Classification Code). For example, a manufacturing plant might employ 100 people and attract 20 people per day that are not employees, on the other hand, a shopping center might employ the same number of people but attract 1000 people. Thus, their trip attraction rates are distinctly different. The Statewide Planning Group of NCDOT provides technical assistance to the DCHC Urban Area transportation planning effort by developing and operating travel forecasting models for the study area. The models are based on a battery of mainframe computer procedures made available by the Federal Highway Administra- tion. The travel forecasting models are comprised of three major parts: trip generation, trip distribution, and trip assignment. The trip generation model provides an estimate of the number of trips produced and attracted by each zone in the study area. Trips are described in terms of Productions and Attractions. Three categories of trips are used: (1) Internal- Internal trips (trips within the study area), (2) External-Internal trips (trips from outside the study area into the study area), (3) External-External trips (trips that travel through the study area but do not stop). 3.1