Flashing Yellow Left Turn Arrows: Scottsdale Experience 2011 Arizona Spring Conference AZITE/IMSA March 9, 2011 Paul Porell, P.E. Traffic Engineering Manager
Innovation Demonstration Project: Presentation today will include: Implementation of Flashing Yellow Left Turn Arrows at two intersections Reasons why this was done Public Outreach and Education Impact on driver behavior Public acceptance Before and After Collision Experience
Flashing Yellow Arrow Background NCHRP Report 493 (2003) looked at numerous displays for P/P left turn control Report recommended use of FYLTA based on high level of driver comprehension and versatility in signal phasing Driver who did not understand indication tended to yield Numerous requests to FHWA approved for experimentation between 2004 and 2006 FHWA Issued Interim Approval for use 3/20/06 NCHRP Report 123 (2007) looked at numerous field installations of FYLTA Improved safety if intersection was P/P before install Safety not improved if Protected only before install No change in safety if Permitted only before install
FYLTA in Scottsdale Scottsdale received interim approval for two locations from FHWA in May 2008 We have identified several additional locations where installation would be beneficial Four intersections along Pima Road between Indian Bend and Via de Ventura will have FYLTA Implementation is easier with ASC 3 then it was with old 170 s which required numerous logic statements
Location No. 1 Raintree at Northsight Northsight Blvd. Raintree Dr. Raintree
Raintree - Northsight Characteristics Heavy southbound left turn demand heading to freeway peaks in PM Dual SB Left turn lanes, single NB left Left turns operated as permitted/protected Numerous citizen complaints of aggressive driving associated with SB lefts (minimum gap acceptance) Collisions between SB lefts and NB throughs
Raintree - Northsight Investigated alternatives Split phasing Protected only phasing Synchro analysis showed that these would significant increase delay and congestion Implemented FYLTA for NB/SB in October 2008
Public Reaction Drivers recognized that FYLTA requires them to yield Number of citizen complaints of aggressive driving went down significantly Received some complaints from drivers who did not understand indication, when questioned they did the proper thing
Location No. 2 68 th St. at McDowell McDowell Rd. 68 th St.
68 th St. and McDowell Characteristics Heavy NB left turn demand Dual NB left turn lanes, single SB left lane Circle K in NW quadrant generates pedestrian activity Valley gutter across north leg slows through movements Identified as high collision intersection by Tempe study of dual left turn intersections Implemented FYLTA in November 2008
Educational Video from WA County
Public Outreach and Education Oct. 20, 2008 Contact: Annie DeChance, Transportation, (480) 312-2526, cell: (480) 406-7153 Flashing yellow turn signals debut in Scottsdale Scottsdale s Transportation Department is installing a new type of traffic signal called a Flashing Yellow Left Turn Arrow to improve safety at two intersections, Raintree Drive and Northsight Boulevard and 68 th Street and McDowell Road. Only the north- and southbound traffic at these two intersections will have the new signals. The signal at Raintree and Northsight will begin operating on Tuesday, Oct. 21. The 68 th Street and McDowell Road signal will begin a few weeks later. The new devices will give drivers more options for turning left and increase safety at the intersections. Currently, both intersections have very heavy left-turn traffic northbound and southbound. The new flashing yellow left-turn signals will provide drivers a better indication that when they turn left, they must yield to the opposing through traffic and pedestrians.
Web Site Educational Material
Collision Experience Raintree/Northsight In 21 months before installation 9 collisions of SB left and NB throughs (5.1 per year) In 26 months since installation 3 collisions of SB lefts and NB throughs (1.4 per year) 68 th St./McDowell In 22 months before installation 6 collisions of NB lefts and SB throughs (3.3 per year) In 25 months since installation 4 collisions of NB lefts and BB throughs (1.92 per year)
Conclusions Use of Flashing Yellow Left Turn Arrows has a positive impact on collision experience when used to replace Green Ball during permitted left turn phase. Growing number of agencies are adopting FYLTA as preferred indication for permitted left Need ADOT to add the four section arrow head to the standard nomenclature Scottsdale continues to be an innovator in Arizona Traffic Engineering
Current ADOT Signal Head Standards
Current ADOT Signal Head Standards
Proposed New Signal Head Type P TYPE P