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Unformatted text preview: CEE 4600 Sight Distance Stopping, Decision, and Passing Fall 2007 Page 1 of 5 Four Aspects of Sight Distance 1. Sight distances needed for complete stopping (applicable for all highways) [ Stopping Sight Distance ]; 2. Sight distances needed for the passing of overtaken vehicles (applicable only on two-lane two-way highways) [ Passing Sight Distance ]; 3. Sight distance needed for decisions at complex locations [ Decision Sight Distance ]; and 4. Criteria for measuring these sight distances for use in design. Stopping Sight Distance The combination of two variables known as the Brake Reaction Distance and Braking Distance. Brake Reaction Time Interval between the instant that the driver recognizes the existence of an object or hazard ahead and the instant that he or she actually applies the brakes (generally assumed to be approximately 2.5 seconds for design purposes). The Break Reaction Time Interval is determined by the driver Perception-Response Time (PRT). PRT time is composed of: Detection object or condition of concern enters drivers field of vision. Identification sufficient information is acquired to allow driver to be a be able to reach a decision as to what action, if any, to take. Decision driver must decide what action is appropriate. Response action is initiated. Brake Reaction Distance Distance traveled by a vehicle during the Brake Reaction Time. This distance is a factor of the vehicle speed and the reaction time. CEE 4600 Concepts and Traffic Engineering Definitions Fall 2007 Page 2 of 5 The approximate distance of a braking vehicle traveling initially at the design speed of...
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- Fall '08