Agenda - Council - 01/11/2022 - Laserfiche WebLink

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Name: Trott Brook Traffic Analysis Date: June 21, 2021 Page: 3 Turn Lanes • Right turn lanes may be justified based on traffic volumes in the direction of the turning movement, roadway speed, daily volume, and in the interest of traffic safety. Since there is already a southbound right turn lane, analysis of need was not determined. • Left turn lanes may be justified based on traffic volumes in each direction, the number of lanes, and the number of left turns during the peak hour of the day. Based on NCHRP 457: Evaluating Intersection Improvements: An Engineering Study Guide, a left turn treatment would be warranted. The MnDOT Road Design Manual indicates that a left turn lane should be provided on a rural highway when the access is to a public road. A left turn lane is also considered to be warranted on a rural, three -leg intersection, with two lanes on a major roadway according to NCHRO 745: Left -Turn Accommodations at Unsignalized Intersections, given the volume of left turns and the traffic on CSAH 5 during the peak hour. • Given the size of the development and the volume of opposing traffic, left turn storage should be provided for approximately two vehicles. • With a 12-foot left turn lane, the roadway speed limit at 55 mph, the storage need, and the preference to not have traffic in the through lane impacted by a slowing left turn vehicle given the two-lane roadway, a left turn lane is recommended to be 565 feet long (385' turn lane plus 180' taper) . • Given the constraints due to Trott Brook, it is recommended that any roadway widening to form a left turn lane be developed north of Trott Brook, approximately 750 feet to the south. Given these constraints, a left turn lane may not be properly developed even if traffic slows by 10 mph in the through lane (50' for vehicles, 170' full width turn lane for deceleration, 180' taper, plus 660' to develop turn lane at speed:1) which would match the design for the southbound right turn lane. • The current southbound right turn lane of 360 feet (full lane plus taper) is considered to be appropriate for 55 mph given a 10-mph slowdown in the through lane. • Separate turn lanes for the eastbound left and right turns on 173rd Ave NW are not required to provide acceptable service levels (LOS C, 16 sec/vehicle average delay in the PM peak), but the separation of turn movements would be recommended due to driver impatience with the amount of right turning vehicles that could potentially be impacted by one left turning vehicle. Conclusions • A northbound left turn lane should be provided if the design can be accommodated since it is justified based on multiple factors, guidance, and manuals. • If a northbound left turn lane cannot be provided due to environmental or other constraints the current bypass lane may be considered acceptable, but an exclusive left turn lane is "the most effective and safe way to separate the left -turning for the through traffic streams" according to the MnDOT Road Design Manual. • An eastbound left and eastbound right turn lane approaching CSAH 5 (Nowthen Blvd) is recommended. Bolton & is an ecpuat opportunity, or. ploy r.