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Pages 8-13

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From page 8...
... 8Measuring Sight Distance and Other Critical Information The purpose of this chapter is to provide users with instructions on collecting field data for the available ISD as well as other relevant data needed to use the guidance. The focus of this guidance is on existing intersections; however, the same field-collected values described here could be determined as part of the design process for a proposed intersection.
From page 9...
... Measuring Sight Distance and Other Critical Information 9 Data Collection Approach Two staff members are required to collect ISD in the field using the approach described here. One person is called the targeter, and the other is the sighter.
From page 10...
... 10 Guidance for evaluating the Safety Impacts of Intersection Sight Distance Traffic Volumes The safety effect of ISD is influenced by two-way AADT and the speed limit on the major street. Generally, the number of crashes increases as the major-road and minor-road volumes increase.
From page 11...
... Measuring Sight Distance and Other Critical Information 11 The reviewer should also identify target crashes using these criteria: • Whether the location of the crash has a milepost within 250 ft of the intersection, and • Whether the crash involved a vehicle on the major road and a vehicle on the minor road. ISD is considered and analyzed by approach direction (or directional analysis unit)
From page 12...
... 12 Guidance for evaluating the Safety Impacts of Intersection Sight Distance be placed on the schematic by approximate location, grouped by accident type, or grouped by intersection sight distance association. Crash diagrams may also be used to help verify whether crashes were target crashes.
From page 13...
... Measuring Sight Distance and Other Critical Information 13 all crashes to determine which are target crashes associated with ISD and which may be singlevehicle crashes or do not involve a vehicle from the minor road. There are four target crashes in this example associated with the left sight triangle, as represented with two arrows pointing at each other.

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