5.2. SR 07-24-2000 - Laserfiche WebLink

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DESIGNING SPEED CONTROLLED SUBDIVISIONS WITHOUT ROAD HUMPS David Szplett and Kuna City Council Member P.O. Box 13 Kuna, Idaho 83634 Phone 208 922-5546 FAX 208 922-5989 Michael Fuess, Civil Engineer Ada County Highway District 318 East 37th Street Boise, Idaho 83714 Phone 208 387-6140 FAX 208 387-6193 ~TRODUCTION Traffic calming is a popular topic for transportation planners and engineers as we try to make subdivisions more liveable. The Institute of Transportation Engineers (ri'E) has even developed a special toolbox of traffic calming measures (1). A common and simple traffic calming approach is to construct road humps, traffic barriers and unnecessary stop signs. Unfortunately, these kinds of measures are often viewed as negative by drivers who are not speeders and sometimes lead to drivers ignoring important traffic control devices. Emergency services providers, especially ambulances, are severely impacted by speed controlling road humps. Road humps also cause noise and are less effective with the increasingly common sport utility vehicles. More driver-friendly solutions are needed. The authors are an elected member of a city council and an engineer employed by a regional highway district responsible for all the local streets and highways in Ada County (Boise), Idaho. The City and the Highway District are jointly responsible for approving the design of new subdivisions and the street system. As such, both agencies must respond to existing concerns over the volume and speed of vehicles on existing streets. Originally, mitigation measures such as road humps were the popular choices. Increasing public complaints have encouraged an alternative approach. The two staffs developed a list of curvilinear roadways, traffic chokers and discontinuous streets to reduce travel volumes and speeds for new subdivisions without the perceived impacts of road humps and unnecessary STOP signs. This paper reports on the results of a three year local planning effort to plan for speed control in subdivision designs. The list of strategies included reduced street cross sections, curvilinear street alignments, shorter block lengths, and the installation of chokers and islands. The following discussion outlines the City's trials and experiences. A summary table is also included. Street Cross Sections The width of the street is an obvious influence on travel speeds. The literature (2) has much discussion on the relationship between roadway width and accident rates. The relationship between roadway width and travel speed is really based more upon the width of the travel lane. The Highway Capacity Manual (3) indicates that roadway capacity drops as the travel lane and shoulder widths narrow.