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MnIDOT Traffic Signal Timing and coordination Manual <br />Question 6 does include a threshold volume of 240 vph for the subject left turn. However, ifthe opposing <br />through volume is low, apply engineering judgment tu detennihe if FYA operation could be used even if <br />the left turn volume exceeds 24Uvph. <br />If permissive FYAoperetion is allowed, protected/permissive operation may be investigated. The decision <br />to use protected/permissive operation should be based an a capacity analysis. <br />Definitions <br />Protected only left turn operation: signal phadng that allows left turn movements toon\yhema�e <br />on an exclusive phase (green arrow). <br />`/ Conflicting' Left Paths: At some locations geometric constraints at the intersection cause the paths of opposing left turn vehicles h| \ to cross as overlap creating m oonf|iut. An example is an approach that crosses odivided roadway with avidamed|on' |nthese locations, itmay benecessary <br />i |t u <br />tuoperate the left tumslUolead-lag sequence oraopU1phase sequence, not a!|uxvingomu oneo s <br />opposing left turns. This operation will require protected left turns. <br />/' opposing through lane (conflict): The opposing through lanes are the lanes across from, and in <br />conflict with, the left turning vehicle. Multiple lanes make itdifficult for adriver toevaluate gaps /n l right turn lane will typically not be counted with opposing <br />oocomin�tre�in'8nopp»sin�uepanzetindicatesthottha|anecon�8urationandnumborof <br />through lanes unless engineering judgment <br />rightturnum/i||cause conf|icLsvviththe |eftturnmovement, <br />vLimited Sight Distance (Requirements): The minimum sight distance values necessary forthe design <br />vehicle volume 10 complete the turn movement. Distance should be ca|zu|oted�onthe stop bar for the mainline left turning vehicle. Measurement |sbased ontravel path, speed, and acceleration <br />nadon <br />Both sight distance for passenger vehicles and trucks should be checked using <br />vehicle height. D»t sD heights and distance 'aquirememsper t the &A3HTOGeometric Design Guide. The current reference <br />2OO4Guyde Chapter Exhibit ott!methismanua|mmupnapareU|szna ' , ' <br />~/ Dual Left Turn Lanes: multiple left turn lanes may consist of exclusive !eft turn lanes or a <br />' and that nen shared by onmb�nationofexdusive|eftturn|ones�n aa �h <br />Both the dual lane and the |eftturn |ono opposing this operation are suggested to operat aw/ <br />phasing. Leftturn lanes without opposing traffic, su h as left turns off of a one- Way <br />protected <br />street does not require protected only phasing based upon this criteria. |tmight also be possible to <br />run the FYAinpermissive mode during low volume times ofthe day. <br />Protectedipermissive left turn operation: signal phasing that provides an exclusive phase (green <br />arrow) followed bvapermisoivaphase (flashing yUowoFrow),time during the signal cydewhere left tumingtraff iomay make oleft turn after yielding tooncoming traffic. <br />' Tu,nDebt�dDd��ooy'ThoseanaCoU�kznsthatcouidbeomrneo�dbvprotectedonlypha�ng, <br />such as those between those � �e� th ' involving e left turning vehicle and on opposing through vahio|e. At <br />f <br />higher speeds the accidents ccollisionsTherefore, o |oxvernumbar o <br />collisions aro|ike\yto he more severe. l|�sionsm|�htbeuseda��heparnmeterforcnnxiderot�onforhi�h-opeadopproaches. Because of f <br />co umberofco||is|unsparyaarnve�o3-Yeorperiod <br />the variations ln collisions overtime, on average n <br />s6bu|dhoused ifthe data |savailable. <br />Spaad^ Because' '� can difficult for, <br />o driver to accurately 'ud8e availab <br />le <br />gaps in traf/o <br />approaching athigh speeds, the oogineermust exercise discretion when considering permissive or <br />protected permissive leftturnphasing with opposing speeds of4SMPH orabove. <br />Moy2O1l <br />Page 13-30 <br />Looa||nt�oactionConoe�s <br />