Agenda - Public Works Committee - 03/15/2022

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Mr. Bruce Westby, PE February 28, 2022 Page 4 Based on criteria from the MnDOT Traffic Signal Timing and Coordination Manual, as there is no significant anticipated crash history for left turning traffic at the intersection and sight distance is reasonable, the City should be able to consider using Flashing Yellow Arrow operations at this intersection during several hours of a typical day. However, due to higher posted speeds and higher peak hour traffic volumes on CSAH 56, along with higher peak left turning traffic volumes on Sunwood Drive, we have concerns about operating with flashing yellow arrow operations on each roadway during these peak traffic periods. Following up further with the Flashing Yellow Arrow Tool for Time-of=Dav Use spreadsheet, we inputted left turning traffic volumes and opposing traffic volumes (combined through and right turning traffic) into the spreadsheet for each intersection approach (with an overall cross product at 80,000 using base conditions of 150 left turns per hour and 533 approaching vehicles per hour). Using this information, the spreadsheet calculates a relative risk factor for having flashing yellow arrow operations during each hour of available traffic volumes. A risk factor of greater than 1.0 indicates that there is a higher risk of a left turn crash based on comparison against base conditions, and the signal is recommended to be operated with protected left turn phasing during those periods. • For northbound CSAH 56, the highest AM peak period risk factor is 0.66, while in the PM peak period the highest risk factor is 0.60. Risk factors exceed 0.6 between 6-8 am and are at 0.6 between 4-5 pm. • For souhbound CSAH 56, the highest AM peak period risk factor is 0.35, while in the PM peak period the highest risk factor is 0.42. • For eastbound Sunwood Drive, the highest AM peak period risk factor is 0.31, while in the PM peak period the highest risk factor is 0.48. • For westbound Sunwood Drive, the highest AM peak period risk factor is 0.37, while in the PM peak period the highest risk factor is 0.71. Risk factors exceed 0.6 between 4-5 pm. Since traffic volumes can fluctuate daily based on several factors, we recommend that the City consider using a risk factor of 0.60 to 0.80 with the currently available traffic counts. This will account for those periods where traffic volumes are fluctuating due to area factors (crashes, bypass traffic, weather, etc.). For our analysis, due to higher posted speeds on CSAH 56, we considered the thresholds for recommending flashing yellow arrow operations as having an approach either exceed/be close to a risk factor of 0.6 or having opposing traffic volumes that exceed 700 vehicles in an hour Utilizing infonnation from both sets of analysis, for both approaches of Sunwood Drive, due to potential concerns about left turning traffic volumes approaching 150 vehicles per hour during the peak PM traffic period, we recormmend considering protected only left turn phasing being used both weekdays and weekends between the hours of 3:30- 5:30 pm. For all other hours of the day and all hours on weekends, protected/permissive flashing yellow arrow operations should be able to be utilized. For the CSAH 56 approaches, concerns about higher opposing traffic volumes along with higher posted speed limits, we recommend considering protected only left turn phasing being used on both weekdays and weekends between the hours of 6:30 am-8:30 am and also between 3:30-5:30 pm. For all other hours of a typical weekday and weekend, flashing yellow arrow operations should be able to be utilized on CSAH 56. Note that any changes in the operation of this signal system should be monitored by the City and Anoka County, including annual review of crash data to ensure that crash frequency does not increase due to the proposed left turn signal operations. Upon further observation and review of the operation of this signal system in the future, there may be the opportunity to extend these hours of flashing yellow arrow operation should the intersection operate safely and efficiently with these proposed modifications. For the time being, we recommend that the City and Anoka County operate the signal system in flashing yellow arrow mode only as noted above.