NARROW RESIDENTIAL STREETS: DO THEY REALLY SLOW DOWN SPEEDS?

Transportation planners and traffic engineers are often asked to consider designing narrow residential streets or narrowing existing wide residential streets as a measure to reduce speeds. Only one of a litany of traffic calming measures, narrowing streets is almost taken for granted to be an effective method of slowing traffic. In addition to literally reducing the curb-to-curb width through design or retrofit, there are several common ways to physically narrow sections of streets including the installation of chicanes, necked curb returns, and tree planters in parking lanes. Some communities indicate success in "perceptive" narrowing of wide streets through painting edge lines or adding bicycle lanes. When considering narrowing residential streets as a traffic calming measure, it is reasonable to ask the following questions: Is street narrowing alone an effective calming measure? How narrow must the street be to dramatically reduce speeds? What other factors affect residential street speed, and what is their relationship? This article presents research into the effect of width on residential street speeds in the San Francisco Bay area.