United States Department of Transportation
i
Effects of Urban Street Environment on Operating Speeds
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2008-01-01
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[PDF-2.73 MB]
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Abstract:Speeds on low-speed urban arterials often exceed their intended operating speeds resulting in potential safety problems since speed is directly related to crash severity, especially for pedestrian-involved crashes. This research develops and calibrates a method for estimating operating speeds based on drivers' perceptions of design features, environmental factors, and operational conditions on low-speed urban roadways. The operating speed model development includes the selection of study corridors that represent comprehensive urban street characteristics, the collection of supplemental data, and statistical model development. This report also includes a review of existing speed models and modeling techniques, common methods used to evaluate driver's perception of the road environment, and possible factors that may influence a driver's speed choice. Low-speed urban streets, as defined in this research, include urban local streets, collectors, and arterials with speed limits less or equal to 45 mph. This study utilizes one year (2004) of data from the Commute Atlanta project, where drivers in the Atlanta, Georgia region freely drove their personal vehicles equipped with data collection equipment. Speed data for free-flow conditions, however, is not straightforward since there is no clear way to determine if a vehicle is operating under free-flow conditions. As a result, this project also includes the development of an extensive free-flow speed filter process. Mixed models are utilized for the estimation of speed conditions. It was found that the use of one robust speed model is not practical for evaluating operating speeds for free-flow conditions for low-speed urban street locations since roadside features have a stronger affect on two-lane, two-way roads than on their four-lane counterparts. Thus, the effort considers two lane and four lane facilities separately and tangent and horizontal curve segments separately. The results from this research effort will aid researchers and designers in pinpointing current problems with the design process and overcoming these limitations using design principals based on appropriate operating speeds that address driver’s perception and reaction to the road environment. The resulting models will provide additional insight into driver selected speeds at urban locations. Future urban street speed model development should benefit from the information contained in this report as it will enable researchers to target specific variable sensitivities.
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Content Notes:FHWA Contracting Officer’s Technical Representative (COTR): Abdul Z. Zineddin, Ph.D.
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