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Mr. Bruce Westby, PE <br />March 21, 2017 <br />Page 2 <br />performed AM peak hour (6-9 am), mid -day (11-1 pm), and PM peak hour (3-7 pm) turning <br />movement traffic counts to determine typical weekday traffic patterns at this intersection. <br />SEH also obtained crash data for the intersection for the 5 year period of 2011-2015 from the <br />State's crash website. SEH then completed a brief field review of the signal system to confirm <br />that the existing traffic signal plans correspond to the current installation of the signal system and <br />take into account the current intersection geometries. SEH also reviewed traffic signal cabinet <br />components to determine if additional electrical equipment would be required to be provided in <br />order to allow for flashing yellow arrow operation to be used. <br />As part of the signal system installation, each intersection approach was set up to operate with <br />protected left turn phasing (3-section RLA-YLA-GLA signals). The intersection has a newer <br />Econolite ASC-3 controller unit and Reno MMU-1600-GE conflict monitor, both of which are <br />fully compatible with upgraded left turn (i.e. flashing yellow arrow) operations. The controller <br />cabinet has sufficient load switch bays available to accommodate flashing yellow arrow <br />operations. Thus, the existing controller and cabinet have the capacity and capability to <br />accommodate future flashing yellow arrow operations for all four intersection approaches <br />without requiring this equipment to be significantly upgraded or revised. <br />As part of our analysis, SEH utilized the Minnesota Department of Transportation's (MnDOT) <br />flashing yellow arrow installation criteria from their "Traffic Signal Timing and Coordination <br />Manual" to analyze extended usage of flashing yellow arrow operations for each intersection <br />approach. A copy of this criteria is attached for your information. Based on comparison of <br />available data with the MnDOT criteria, the following can be inferred: <br />The design of this signal system included the initial recommendation of protected left <br />turn phasing for each intersection approach due to the higher posted speed limit of 55 <br />mph on CSAH 83 (as is typical Anoka County practice) and the presence of a dual left <br />turn lane for the westbound Sunwood Drive approach. <br />With regards to utilizing Flashing Yellow Arrow operations for each left turn movement, <br />the following should be noted: <br />• According to the current edition of the AASHTO Geometric Design ofHighways <br />and Streets manual, left -turning drivers "need sufficient sight distance to decide <br />when it is safe to turn left across the lanes used by opposing traffic." This <br />stopping sight distance along CSAH 83 for the design/posted speed of 55 mph is <br />at least 495 feet of clear sight distance to the north and south. For both Sunwood <br />Drive and 147th Avenue Northwest, the recommended stopping sight distance at <br />30 mph is as least 200 feet to the east and west. Based on a field review of <br />intersection geometrics, the southbound, eastbound, and westbound intersection <br />approaches are straight for several hundred feet in each direction with no <br />impediments to the sight distance (other than possible sun issues for eastbound <br />