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28 Residential Streets <br />rounding areas can be accurately predicted. The place in the hi- <br />erarchy assigned to a particular residential street can and should <br />relate to its particular traffic projection. <br />Average daily traffic (ADT) —the average total number of vehi- <br />cles traversing a highway or route on a typical day —is one factor <br />in the design or alteration of highways and arterial streets, but it <br />should not be the sole factor. A generalized classification scheme <br />is presented in Table 2 -1; however, the ADT ranges may overlap <br />and thus are not intended as design criteria. <br />Table 2-1 <br />Street Classes Based upon Traffic Volume <br />Class Usual ADT Range <br />Access Street 0 -250 <br />Subcollector 250 -1,000 <br />Collector 1,000 -3,000 <br />ADT is not considered the best index for local residential street <br />design. The traffic density and consequences of highway and ar- <br />terial street speeds are absent on subdivision streets, and residen- <br />tial driving attitudes and habits differ from highway and arterial <br />driving behaviors. Yielding momentarily to resolve minor residen- <br />tial traffic conflicts is practical at residential -area speeds. Either <br />residential traffic yields to drivers backing from their driveways, <br />or backing drivers yield to oncoming traffic, and no one is unduly <br />delayed. When parked vehicles impede residential traffic, ap- <br />proaching vehicles often yield and then proceed with caution. In <br />part, designs that encourage this kind of cautious driver behavior <br />result in reduced speed, greater attention on the part of drivers to <br />conflict, and, thus, safer streets. <br />The primary considerations in selecting residential street stan- <br />dards, therefore, are the characteristics of Local residential traffic <br />and residents' expectations. Traffic volumes can provide additional <br />guidance for decision making. <br />Most sources estimate that the average daily traffic (ADT) per <br />single - family detached dwelling unit ranges from eight to 10 ve- <br />hicles per day. Attached units and multifamily units tend to gen- <br />erate fewer trips. Surveys performed by the Institute of Transpor- <br />tation Engineers have yielded the following: <br />Page 8 <br />