5.2. SR 07-24-2000 - Laserfiche WebLink

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Locally, the standard width of a residential street in a new subdivision is 37-feet (measured back-of- curb to back-of-curb). This allows two 8-foot travel lanes plus the mandatory 20-foot travel lane for' emergency and large vehicles. A 29-foot width is allowed on low volume streets with a parking prohibition on one side. The standard residential speed limit is 25 MPH. A traffic calming program is also in place. Traffic calming is typically imposed with road humps and otherwise unneeded STOP signs. A review of streets already inflicted with traffic calming measures has shown that even 29-foot streets with two-sided parking have problems with excessive traffic volumes or speeds. The concern with traffic calming has led to a proposed policy allowing 29-foot streets with two-sided parking as a new standard. Although developers are supportive of the lower construction costs and larger lots resulting from the narrower streets, they believe that 29-feet is too narrow and usually design 32-footers instead. The realtors report that potential homeowners are uncomfortable with such narrow streets. Traffic surveys have shown that the average travel speeds are about equal for the 29 and 32-foot streets (e.g, 28 MPH) and the emergency services seem more willing to accept them. The 85th percentile for the standard street design is 30 MPH. In Kuna, neither the trash truck drivers nor the parcel delivery services have expressed a concern with 32-foot streets. We did find that some drivers will park on the sidewalk if they think that the streets are too narrow. Either vertical curbs or small planter strips can prevent this from happening. Street Alignment Similar to the narrower street sections, a curvilinear street alignment reduces the driver's sight distance and tendencies to speed. Long straight streets seem to encourage speeding. A review of streets already inflicted with traffic calming measures did not give us a clear picture of the effect of street alignment. There are too many other variables to isolate that one design feature. The local traffic calming program calls for road humps a minimum of 600-feet apart. With 600-feet then as the goal for a maximum sight distance, the desired street curve radius was set at 350-feet. Although a smaller radius would reduce speeds even further, developers had more difficulty designing their subdivisions. The 350-foot goal seems to be an acceptable compromise between speed control and ease of design. Intermediate tangent roadway sections of less than 600-feet appear to provide the needed results. Traffic surveys have shown that although 85th percentile of 27 MPH speed is very close to the 25 MPH signed speed limit, the curved street appears to have stopped the number of drivers exceeding the speed limit by more than 10 MPH. Because there are minimal problems with speeding, the 37- foot street sections are acceptable with this design. Chokers and Islands Traffic chokers and median islands are alternative methods of restricting the width of both the travel