2019.08.07 EDC Packet - Laserfiche WebLink

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Traffic Impact Study 3 New Brighton Exchange Update c. Intersection Sight Distances Proper sight distance can reduce the possibilty of conflicts at intersections. Therefore, the sight distances were evaluated at the three stop controlled study intersections. According to the American Association of State Highway and Transportation Officials' (AASHTO) A Policy on Geometric Design of Highways and Streets (commonly referred to as the Green Book), the driver of a vehicle approaching an intersection should have an unobstructed view of the entire intersection, including any traffic-control devices, and sufficient lengths along the intersecting highway to permit the driver to anticipate and avoid potential collisions. Intersection sight distances were sampled at both stop sign approaches at each of the three locations on Old Highway 8. Intersection sight distance is distance provide d at intersections and driveways to allow drivers to perceive the presence of potentially conflicting vehicles and, when the appropriate gap in traffic is provided, to safely perform their movement. Intersection sight distance requirements are provided in terms of both a physical distance and a time gap in the mainline traffic related to the speed of approaching vehicles. For approaching vehicles at any speed, per Table 9-5 of the AASHTO Green Book, a passenger car stopped at an intersection requires a min imum time gap of 7.5 seconds in either direction to complete a left turn movement. In other words, an average driver needs to see an approaching vehicle at least 7.5 seconds away to know if they have sufficient time to complete a left turn. To complete a r ight turn movement, per Table 9-7 of the AASHTO Green Book, the time gap is reduced to 6.5 seconds for a passenger car and applicable only to vehicles approaching from the left of the stopped driver. For single-unit trucks, the time gaps are 9.5 seconds for a left turn and 8.5 seconds for a right turn. For combination trucks, the time gaps are 11.5 seconds for a left turn and 10.5 seconds for a right turn. Five vehicle time measurements were made at each location and those times were averaged. Table 1 shows those results. The results in Table 1 are based on measurements made in a passenger vehicle. The times may be larger for single -unit or combination trucks as the driver is seated higher in those vehicles increasing the field of view.