The Variable Number of Left Turn Lanes (VNLTL) treatment is a method of varying the number of left turn lanes available for a given approach at a signalized intersection – and the associated left turn signal phasing for that approach and/or the opposing approach – by time-of-day.

Under VNLTL for a given approach, all left turns are made from the left-most left turn lane during normal, off-peak operation, which improves sight distance for those turning vehicles. Closing the adjacent, right-most left turn lane also improves sight distance for the opposing left turns. This can enable “permitted” left turns and reduce delay.

 

Benefits of VNLTL treatment

  • Mitigates or eliminates the “peak capacity vs. off-peak delay” tradeoff
  • Eliminates requirement to show the restrictive protected-only phase when such a phase is not needed
  • Lowers off-peak delay, by reducing both the number and duration of required signal phases
  • Potentially reduces peak delay, by mitigating the tradeoff of building a second left turn lane
  • Increases operational flexibility, on a time-of-day, approach-by-approach basis

 

Design and operational information

 Signs, signals, and markings

  • Static left turn only (R3-5L) signs are posted above the left-most left turn lane
  • LED lane use control signs are posted above the right-most left turn lane
  • A single, four section head is installed above the lane line between the two left turn lanes
  • Left turn lane pavement markings are consistent with typical dual left turn lane installations

 

Normal, off-peak operational practice

  • Only the left-most left turn lane is available to turn left
  • The right-most left turn lane is closed, with a red “X” displayed in the LED lane use control signs
  • The signal includes flashing yellow arrow to provide protected-permitted left turn operation

 

Peak period operational practice

  • The right-most left turn lane also becomes available to serve left turns
  • A left turn arrow and “ONLY” is displayed in the LED lane use control signs
  • The signal suppresses the flashing yellow arrow to provide protected-only left turn operation

 

Design and operational notes

  • The single left turn signal serves and controls both left turn lanes
  • One set of left turn lane signs are installed at the signal itself, directly over the center of the lanes
  • A companion set of left turn lane signs are installed in advance, serving the entry to the turn lanes
  • Left turn phasing can vary by approach as well as by time-of-day, depending on each cross product

 Click here for this overview, including a graphic of the installation treatment

Click here for a list of FAQs, including a graphic of the installation treatment


For questions about the innovative VNLTL treatment, please contact:

Joe Milazzo II, PE
Executive Director, Regional Transportation Alliance
919.664.7065
joe@letsgetmoving.org

RTA is the voice of the regional business community on transportation