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M E M O R A N D U M <br /> 12/2/91 <br /> <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 /> develop~ent 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 /> <br /> which might be considered pass-by in nature, the methodologies provide for a <br /> p.m. peek 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 squire footage cap were used for comparative purposes. The basic concept <br /> was to provide similar proportional 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, aid 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 /> analys7s, 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 />