Agenda - Public Works Committee - 10/19/2021

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1 C 3 f �� Tra xc Sign Timing and coordination Manual � l�In,�l�T � �. t o the subject left turn. However, if the opposing Question 6 does include a threshold volume of 24Q vph for • • etermirie if FYA operation could be used even if through volume is lour, apply engineering judgment to d p g e exceeds 240 vph. the leftturnvolurn • - protected/permissive ermissive operation may be investigated.The decision is f permissive FYA operation is allowed, p p ' - If p missive operation should be based on a capacity analysis. to use protected per p Definitions d ® eration:signal phasing that allows left turn movements to only be made � Protected only left turn p g f on an exclusive phase(green arrow)• constraints at the intersection cause the V Conflicting Left Turn paths: At some locations geometric• vehicles to cross as overlap creating a conflict, An example is an paths of opposing left turn v apprioach that crosses a divided roadway with a wide median,In these locations,it may be necessary �. a lead-la sequence or a split phase sequence,not allowing simultaneous � to operate the left turns in g se q t turns. opposing left turns.This operat•�or�will require protected lei pp • sing through lanes are the lanes across from, and in opposing through lane (conflict): The upo g g • to evaluate gaps in . vehicle., Multi le lanes make it difficult for a driver g p conflict with,the left turning p e counted with opposing F traffic.An osing separate right turn lane Will typically not b oncoming pp • judgment indicates that the lane configuration and number of through lanes unless engineering , • conflicts with the left turn movement, right turns will cause confl� % • s •The minimum sight distance values necessary for the design � Limited Sight Distance(Requirement . fiance should be calculated from the stop bar vehicle volume to complete the turn movement. Des acceleration • turnip vehicle. Measurement is based on travel path,speed,and a • for the mainline left g • e sight distance for passenger vehicles and trucks should be checkedusing vehicle height. Both the g • " ements per the AASNTo Geometric Design Guide. The current reference heights and distance requtr p g Exhibit�--6�' at time this manual was prepared is the 2004 Guide,Chapter , lanes may consist of exclusive left turn lanes or a � Dual Left Turn Lanes: Multiple left turn y • turn lanes and lanes that are shared by through and left turning traffic. rn co bination of exclusive left lane opposing this operation are suggested to operate with Bath the dual lane and the left turn pp g turns off of a one-Way ed phasing. turn lanes without opposing traffic, such as left protected p g ,terra. It might also be possible to street does not require protected only phasing based upon this cri g run the FYA in permissive mode during low volume times of the day. p turn operation: signal phasing that provides an exclusive phase {green rotected ermissive left - p I� permissive phase (flashing yellow arrow), time during the signal cycle wherearrow� fallowed by a perms p turnip traffic may make a left turn after yielding to oncoming traffic. left g �. collisions that could be corrected by protected only phasing, G Left Turn Related collisions:These are ose involvin a left turning vehicle and an opposing through vehicle, At such as thane between th g s are likely to be more severe, Therefore, a lower number of higher speeds the accidents collision � approaches, Because of eed- hi hs collisions might be used as the parameter for consideration for high-speed the variations in collisions overtime, an average number of collisions per year over a 3-year period should be used if the data is available. ' curatel judge available gaps in traffic speed: Because it can be difficult for. a driver to ac y g l permissive or ' at high speeds,the engineer-must exercise discretion when considering approaching g p with opposing speeds of45 MPH or above. protected permissive leftturn phasing pp g Page 3-34 Local Intersection Concepts May2011 f" f