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Ms. Jane Rose October 12, 2015 Page 4 consider using Flashing Yellow Arrow operations at this intersection throughout much of a typical weekday and throughout the weekend. In addition, any changes to the operation of the left turn signal phases are not anticipated to impact overall operations of the intersection in a negative way (and delays for left turning traffic will decrease with flashing yellow arrow operations which will improve the overall operation of the intersection). For peak traffic periods though (and for when sun becomes an issue for eastbound and westbound traffic), protected left turn operation is strongly recommended to be implemented. Note that for the existing signal system to the east along CSAH 14 (at 2111 Avenue North), the signal system has flashing yellow arrow capability. However, during peak traffic periods, this signal system is operated in protected left turn mode. Some modifications to the existing signal system installation will be required to revise the operation of this signal system and add flashing yellow arrows for each intersection approach. Both overhead end mounted and far left pole mounted left turn signals for each intersection approach will required having 3 - section RLA-YLA-GLA signal heads replaced with 4 -section RLA-YLA-FYLA-GLA signal heads. For the southbound approach, due to the dual left turn lane, a 5 -foot extension will.be required to be added to the southwest mast arm so that two 4 -section overhead signals can be installed and centered on each left turn lane (requirement that each approaching left turn lane have its own flashing yellow arrow signal centered on each left turn lane). Some additional cabling (6/6#14) will be required to be installed to operate these signal heads based on a review of the field wiring diagram. No additional through traffic signal heads will be required to be installed as each approaching through lane has its own separate signal centered on the lane. With regards to left turn lane detection, the MnDOT Traffic Control Signal Design Manual recommends that either four loop detectors be installed for proper detection (at 5', 20' 35' and 50' from the stop bar or crosswalk) or that two separately wired loop detectors be installed for existing signal system retrofits at 10' and 40' from the stop bar or crosswalk. For this signal system, left turn lane detection was installed at 0' and 15' from the stop bar (wired together as one loop detector). To provide better coverage, fall back detection should one channel of left turn lane detection fail, and meet MnDOT criteria for flashing yellow arrow detection, we recommend that one additional loop detector (separately wired and operated on a separate channel in the controller cabinet) be furnished and installed in each left turn lane. The two stop bar loop detectors can be left as is on one channel, with a second loop detector being installed at 40 feet from the stop bar and wired separately. This would require that 5 additional loop detectors, five new 2/c#14 cables, and three 2 -channel loop detector cards be installed to bring these loop detector installations up to current flashing yellow arrow design and operational standards. To allow for flashing yellow arrow operation, we estimate that these modifications (completed by an electrical signal contractor) will cost approximately $28,500. This does not include potential conflict monitor upgrade. A detailed preliminary engineer's estimate of costs is attached to this letter for your information. Overall, we do not see any issues with installation and operation of flashing yellow arrows for each intersection approach. However, should the County implement flashing yellow arrow modifications to this signal system, we recommend that the signal system operate with protected left turns during both the AM peak period (6:00-10:00 am) and the PM peak period (3:00-7:00 pm) due to significant traffic volumes and higher posted speeds through this area. For all other hours of the day and for all weekend hours, the County should be able to consider using flashing yellow arrow operations. 126