Agenda - Public Works Committee - 03/15/2022

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Mr. Bruce Westby, PE February 28, 2022 Page 2 The eastbound approach has a separate left turn lane, a single through lane, and a separate right turn lane. The westbound approach has a separate left turn lane and a shared through/right turn lane. The intersection has an older controller cabinet WITHOUT sufficient load switch bays open and available to allow for flashing yellow arrow operations to be added for all four intersection approaches. It is recommended that this controller cabinet be replaced with a newer controller cabinet with capacity and capability to accommodate future flashing yellow arrow operations for all four intersection approaches. The controller unit is an older Econolite ASC 25-2100 unit that is not capable of operating flashing yellow arrows and will be required to be replaced. The conflict monitor is an older EDI-SSM-I2LE unit, also incapable of operating flashing yellow arrows. Thus, in order to be able to convert all intersection approaches to operate with a flashing yellow arrow, we recommend that the controller cabinet, controller unit, and conflict monitor all be replaced. As part of our analysis of whether and when to operate the signal system with flashing yellow arrows, SEH utilized two sets of criteria as shown on the Minnesota Department of Transportation's (MnDOT) Office of Traffic Engineering (OTE) web site: flashing yellow arrow installation criteria from their "Traffic Signal Timing and Coordination Manual", and the Flashing Yellow Arrow Tool for Time -of -Day Use spreadsheet that incorporates various criteria to determine a relative risk factor for enacting flashing yellow arrows based on intersection geometries and turning movement traffic count volumes. With regards to utilizing Flashing Yellow Arrow operations for each left turn movement, please note the following: According to the current edition of the AASHTO Geometric Design of Highways and Streets manual, left - turning drivers "need sufficient sight distance to decide when it is safe to turn left across the lanes used by opposing traffic." This minimum required stopping sight distance along CSAH 56 for the design/posted speed of 55 mph is at least 495 feet of clear sight distance to the north and south. The stopping sight distance along Sunwood Drive for the design speed of 30 mph is at least 200 feet of clear sight distance to the east, and for 35 mph is at least 250 feet of clear sight distance to the west. Based on a field review of intersection geometries, we estimated stopping sight distance on each CSAH 56 approach to be exceeding 1,000 feet. The stopping sight distances for both eastbound and westbound Sunwood Drive are also exceeding 1,000 feet. However, note that in the Flashing Yellow Arrow Tool for Time -of --Day Use spreadsheet, sight distance for left turning traffic at the stop bar in each left turn lane is calculated based on the distance between stop bars, left turn lane offsets (measured from the lane line of the near side left turn lane and the edge of median on the far side approaching left turn lane), and other standard lane and vehicular measurements. 1. Based on plan measured distances and criteria proprietary to the spreadsheet, available sight distance for each CSAH 56 approach was calculated at around 270 feet in each direction (mostly due to potential blocking of approaching sight distance by opposing left turning traffic). If no opposing left turning traffic is present for a left turn movement, sight distance would be estimated to be exceeding 1,000 feet. 2. For the Sunwood Drive approaches, based on plan measured distances and criteria proprietary to the spreadsheet, available sign distances for both approaches were calculated to be in excess of the 365 feet required for safely accommodating flashing yellow arrow operations (mostly due to potential blocking of approaching sight distance by opposing left turning traffic). If no opposing left turning traffic is present for a left turn movement, sight distance would be estimated to be exceeding 1,000 feet. Based on both criteria, there are sight distance concerns on each intersection approach when there is opposing left turning traffic but no concern if the opposing left turn lane is empty. • Based on the recent crash history at this intersection, a total of 6 crashes were reported between January 2017 and December 31, 2021. 2 crashes were reported in 2018, 1 crash in 2019, 2 crashes in 2020, and 1 crash was reported in 2021.