Approximately 27% of all intersection crashes in the United States are associated with left turns, with more than two-thirds of those occurring at signalized intersections. Various traffic signal control strategies have been implemented to balance concerns about both the efficiency and safety of left-turning traffic.
In spring 2010, the Illinois Department of Transportation (IDOT) integrated the flashing yellow arrow (FYA) as the display for the left-turn permissive interval at more than 100 intersections in the Peoria area that operated with protected/permissive left-turn (PPLT) control. This short video provides a closer look at how these signals work. At more than half of the those intersections, a supplemental sign was also installed with the text “Left Turn Yield on Flashing Yellow Arrow.”
In fall 2010, the Illinois Center for Transportation (ICT) initiated a study on behalf of IDOT to evaluate the effectiveness of FYAs. ICT investigator Kerrie Schattler, professor in the Department of Civil Engineering and Construction at Bradley University in Peoria, led the study. The research tasks included performing comprehensive traffic crash analyses, conducting field studies of traffic operations and conflicts, and assessing driver comprehension of FYAs.
The traffic crash analyses were based on three years of crash data both before and after the FYA installation, as well as three years of data at 100 comparison sites. A total of 164 approaches and 86 test intersections were evaluated. Analyses were also performed to assess the effects of the FYA on older drivers (age 65+) and younger drivers (age 16 to 21 years).
Schattler says they analyzed 3,307 crash reports in the study but faced some challenges at times. “According to a national survey, it can take 6 months up to a year after a crash occurs before the data becomes available in a statewide database. Early on in our project, the crash data was readily available, but it began to take longer as the project end date was approaching. However, with the help and support of IDOT—particularly Priscilla Tobias and our project’s Technical Review Panel chair Randy Laninga, we were able to expedite the process and deliver our research results on time.”
Laninga is the Design and Planning Engineer at IDOT District 4 in Peoria. Tobias, Director of the Office of Program Development at IDOT, currently serves as State Safety Engineer as well.
In analyzing that data, the researchers found a 23.3% reduction in left-turn-related crashes and a 24.8% reduction in left-turn opposing-through crashes at the studied FYA approaches. They also found a significant reduction in crashes at FYA approaches with the supplemental signs: 31.9% and 30.9% for left-turn-related and left-turn opposing-through crashes, respectively.
For the older driver/younger driver analysis, the research team found that the FYA did not show a significant effect in reducing the crash rate of older drivers, but the arrow did bring reductions in the crash rate for younger drivers. Schattler says that as the percentage of older drivers increases, the traffic safety community must continue to be sensitive to the needs of older drivers and increase public awareness and education for this group of drivers, especially with regard to new traffic control messages and displays.
Laninga says, “I feel that the findings of this project show that flashing yellow arrows will be a great benefit to the people of Illinois by reducing the type of left-turn crashes that can be very serious. And it’s worth noting that this increase in safety was accomplished with no reduction in intersection capacity, and it offers the possibility of achieving better progression of traffic on arterials.”
He adds that IDOT is developing a new policy that will require the use of FYAs at signalized intersections unless financial or design impediments would prohibit them.
The full report, Safety Evaluation of Flashing Yellow Arrows for Protected/Permissive Left-Turn Control, is available on ICT’s website. Earlier reports published in connection with this project are also available online: State-of-the-Art Literature Review on Permissive /Protected Left-Turn Control and Driver Comprehension and Operations Evaluation of Flashing Yellow Arrows.
Originally published May 19, 2016.