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A was shown in th <br /> As as sho n Figure 1, the travel demand modeling process was broken into two <br /> parts. First, the existing transportation system usage was replicated using existing <br /> socio-economic data. Trip generation, distribution and assignment calculations were <br /> adjusted as necessary to create a model that allocated traffic to the existing roadway <br /> network such that assigned volumes were as close as possible to actual measured <br /> volumes. This was done to validate the travel behavior factors that would be used <br /> in the ultimate forecast. When enough adjustments had been made to arrive at a <br /> reasonably close replication, the socio-economic forecasts for ultimate development <br /> were used to create an ultimate travel demand forecast. The following sections <br /> describe the components of the process in greater detail. <br /> 1. Trip Generation <br /> In the trip generation process, generation rates are applied to the chosen <br /> socio-economic parameters to estimate the number of vehicle trips to and <br /> from each TAZ to be placed on the roadway network. A trip generated may <br /> be either a trip into or out of a TAZ; generally, no distinction is made when <br /> dealing with Average Daily Traffic (ADT)volumes. Rather,the reasonable <br /> assumption is made that in a given 24-hour period on a weekday, the total <br /> number of trips into and out of any TAZ is approximately equal. This is not <br /> the case in a peak hour analysis, where trips into and out of a TAZ can differ <br /> greatly depending on the types of generators it contains. The Elk River study <br /> was done using ADT volumes. <br /> The general reference used in determining trip generation rates was the 5th <br /> Edition of the Institute of Transportation Engineers Trip Generation Manual, <br /> published in 1991. Information on generation rates for various land uses was <br /> obtained from this document and modified according to specific <br /> characteristics of the City of Elk River. <br /> Table 2 shows the various trip generation rates that were used in Elk River. <br /> Two residential rates were used: one, 9.0 trips per household if the average <br /> household size in the TAZ was greater than 3.0 people, and the other, 8.5 <br /> trips per household for TAZs with average household sizes of 3.0 or less. <br /> Two rates were used to reflect the tendency of larger households to generate <br /> ' more trips. <br /> The generation rate for low-density highway commercial was considerably <br /> lower than the rate for general highway commercial. This was meant to <br /> reflect on those areas further from the core of the City that are zoned highway <br /> commercial but have less intense land uses than general retail, such as auto <br /> dealerships and other showrooms. <br /> External trip generation was handled in an entirely different manner. Each <br /> important road crossing the City border was considered an external zone. <br /> The existing rip generation for each of these zones was simply the existing <br /> traffic volume count on that road at the City border. To estimate the external <br /> volumes at the point in time when ultimate development in the City of Elk <br /> River is achieved,the year of ultimate development had to be estimated. This <br /> jCTP-230.156 -7 230-156-80 <br />