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M E M O R A N D U M <br />12/2/91 <br />T0: Mike Gleason, City Manager <br />Christine Andersen, Public Works Director <br />FROM: Brant Williams, Traffic Engineer <br />SUBJECT: Proposed Revisions To SDC Methodologies <br />Recently, a building permit to add eight pumps to an existing service station <br />brought to light a problem with the newly adopted methodologies for systems <br />development charges. Section 3.2 of the methodologies has provisions to <br />account for development-related trips that are not actually added to the <br />adjacent street system but are generated from the existing stream of traffic. <br />These are called pass-by trips. To adjust for pass-by trips for developments <br />which might be considered pass-by in nature, the methodologies provide for a <br />p.m. peak hour cap of 10 trips per one thousand square feet of building de- <br />velopment. <br />Service stations are considered pass-by in nature. However, their trip rate <br />is not calculated on a square footage basis. The ITE Trip Generation Manual <br />uses the number of gasoline pumps as the unit of measurement, and thus, the <br />cap based on square footage cannot be applied. To provide an adjustment for <br />service stations, the methodologies document needs to be revised. <br />To determine an appropriate cap per gasoline pump, other developments meeting <br />the square footage cap were used for comparative purposes. The basic concept <br />was to provide similar proportion a7 adjustments for pumps as those for square <br />footage calculations. However, the proportional adjustments are different <br />for the dozen or so developments already capped. Thus, other methods were <br />considered including using the average and/or the median of the existing <br />caps, and using the highest and the lowest proportional adjustments for the <br />existing caps. One other method used was based on actual surveyed number of <br />pass-by trips for service station-type developments. In considering all <br />these methods, the range of possible caps was very large. <br />To arrive at an equitable cap, total generated trips for various currently <br />capped developments were determined using typical building sizes. These <br />results were then compared to the range of capped total trips for a typical <br />size service station. It turns out that the averaging method produces a <br />total number of trips for a typical service station that is reasonable and in <br />line with total trips for other typical capped developments. Through this <br />analysis, the recommended cap is 5.10 trips per pump. This is a 66% reduc- <br />tion of the actual measured ITE trip rate of 15.18 trips per pump. <br /> <br />