Flashing Yellow Arrow Research Articles

Safety Effectiveness of Flashing Yellow Arrow

The purpose of this project was to develop crash modification factors (CMFs) for the implementation of a flashing yellow arrow (FYA) on the basis of the specific before-and-after period conditions of a signalized intersection. Although this countermeasure has been used for years in North Carolina and other states, no published studies to date have provided CMFs for left-turn crashes specific to the treated approaches, and none has provided CMFs for the three-section FYA for permissive-only left turns. Crash data from 222 intersections in North Carolina with an FYA protected–permissive left turn (FYA-PPLT), three-section FYA permissive-only left-turn installations, or both were used to provide CMFs for five category types: Category 1 (permissive only to FYA-PPLT), Category 2 (protected only to FYA-PPLT), Category 2A (protected only to FYA-PPLT with time of day operation), Category 3 (five-section PPLT to FYA-PPLT), and Category 4 (permissive only to FYA permissive only). A before-and-after crash analysis with consideration given to increases in traffic was used to determine the safety estimates. Safety performance functions were used to account for the effect of traffic volume trends. In Categories 3 and 4, the change was exclusive to the left-turn display and not to a change in phasing. All CMF results were statistically significant for Category 3, and target and injury CMF results were statistically significant for Category 4. On the basis of the results from the study sites, a statistically significant decrease was found in target left-turn crashes and injury crashes after a site signal underwent a change from a solid green ball to an FYA for permissive left turns when phasing remained unchanged. This finding applied whether the left phasing was protected–permissive or fully permissive.

Safety effects of traffic signing for left turn flashing yellow arrow signals

In 2010, the left turn flashing yellow arrow (FYA) signal displays were installed at signalized intersections on state routes in the Peoria, Illinois, area. Supplemental traffic signs with text “Left Turn Yield on Flashing Yellow Arrow” were mounted on the mast arm adjacent to the left turn signal at over half of the FYA installations. The purpose of this paper is to present the results of the effectiveness evaluation of the FYA supplemental sign on safety. Analyses are presented on the effects of the FYA supplemental sign for all drivers and a subset of drivers age 65 and older. A crash-based comparison of 164 FYA approaches including 90 approaches with the sign and 74 approaches without the sign showed greater crash reductions when the supplemental FYA sign was present. The results also showed that crashes involving drivers age 65 and older did not experience the same magnitudes of crash reductions as compared to all drivers. The findings of this research indicate that supplemental FYA signs may help in improving safety for left-turning vehicles during the permissive interval. Thus, it is recommended that supplemental signs be used when initially implementing the FYA, and that effort to educate the driving public on new traffic control be made to further improve safety at signalized intersections.

Safety and Operational Impacts of Optional Flashing Yellow Arrow Delay

Considerable debate exists over whether to delay the start of the flashing yellow arrow (FYA) signal indication (e.g., with a red arrow signal indication) during the transition from a protected movement to a permissive movement in a leading left protected–permissive left turn. The 2009 Manual on Uniform Traffic Control Devices is silent on this topic. This paper reviews the state of the practice on the use of the optional FYA delay through a literature review, a survey of state departments of transportation, and consultations with practitioners and national experts. A simulation study was also used to assess the potential impacts of the optional FYA delay on traffic safety and operations. The state-of-the-practice review indicated some preference for the use of the red arrow signal indication because of the perceived safety benefit. For example, 71% of the responding state departments of transportation that use the FYA also delayed the start of the FYA. The simulation analysis showed significant safety benefits in a delay to the start of the FYA signal indication for all scenarios except the scenario with a low opposing through traffic volume, with no significant negative impacts on average delay, average queue length, or average stopped delay for either left-turning traffic or the intersection as a whole being found.

Three- or Four-Section Displays for Permissive Left Turns?

Many jurisdictions are using the flashing yellow arrow (FYA) to control protected and permissive left turns. For cost and other reasons, some jurisdictions have or are considering implementing FYA with a three-section vertical head, displaying the flashing yellow indication in the same signal face as the protected green arrow. The current Manual on Uniform Traffic Control Devices permits the operation of a three-section vertical head only for permissive turns in locations where heights are restricted. This paper summarizes a comparison of driver performance with three- and four-section FYA signal configurations gathered in a high-fidelity, motion-based driving simulator with mobile eye-tracking equipment. The experiment controlled for the effects of the opposing traffic, the presence and walking direction of pedestrians, and the signal head arrangement. A 24-intersection simulated environment was created, and 27 subjects completed the course, producing 620 permissive left-turn maneuvers for further analysis. Driver performance was measured from the (a) average total eye glance durations at specific areas of interest and (b) the position of the pedestrian in the crosswalk when the driver initiated the left turn. No statistically significant differences between the average fixation duration when the FYA was presented with a three- or four-section signal head were identified. The pedestrian's position in the crosswalk when the driver began the left turn was not statistically significantly different for three of the four pedestrian walking directions presented. Overall, measurable driver performance does not seem to be sensitive to the vertical positioning of the FYA display in the permissive interval.

Assessing the effect of introducing a permitted phase through the use of flashing yellow arrow signal for left-turning vehicles

This paper evaluates the direct and indirect effects of introducing a permitted phase, through the use of flashing yellow arrow (FYA) signal for left-turning vehicles, in reducing crashes at intersections. Data for 18 study intersections in the city of Charlotte, NC, USA were used to conduct a before–after comparison study through the use of Empirical Bayes (EB) method and examine the effects. The estimated number of left-turn crashes, had the FYA signal not been installed, was compared to the actual number of left-turn crashes to assess the direct effect, while the estimated total number of crashes, had the FYA signal not been installed, was compared to the actual total number of crashes to assess the indirect effect. Only left-turn crashes along a selected FYA leg were used to examine the direct effect as the number of legs (approaches) with the FYA signal varied between the selected study intersections. The results obtained indicate that the FYA signal helps reduce the left-turn crashes (direct effect). It does not lead to any negative consequences. Instead, the FYA signal has the potential to indirectly lower the total number of crashes (indirect effect) and contribute to improved safety at intersections.

Behavior of Left-Turning Drivers during Permissive Interval of Protected–Permissive Operation

A study was conducted to assess the differences in operations and driver behavior in response to three signal displays for the permissive interval of a protected–permissive left-turn (PPLT) phase. A comparative two-phased approach based on field observations and video recordings of driver behavior was used to conduct the research. Phase 1 examined driver behavior at six intersection approaches in Peoria, Illinois, that operated with different permissive left-turn displays: circular green (CG), flashing yellow arrow (FYA), and flashing red arrow (FRA). The CG indication had been the predominant indication used for the left-turn permissive indication in Peoria until 2010, when FYAs were installed throughout the city. FRAs are operated at two adjacent intersections in Peoria and were installed as a site-specific countermeasure. The Phase 1 findings showed that the highest proportion of drivers' safe and efficient actions was in response to the FYA as compared with the CG and FRA displays. In Phase 2, a comparative analysis of four intersection approaches was conducted to determine the impact on driver understanding of the permissive left-turn CG display in two geographic areas: one in Peoria, where multiple permissive left-turn signal indications for the PPLT phase (CG, FYA, and FRA) are currently in use, and one in Blooming-ton, Illinois, where only the CG indication is used. The Phase 2 research found, on the basis of observed safe and efficient driver actions, that there were no differences in driver understanding of the CG permissive left-turn display at the study approaches in the two cities.

Evaluating Effect of Two Allowable Permissive Left-Turn Indications

NCHRP Report 493 recommended that a flashing yellow arrow (FYA) permissive indication be included in the Manual on Uniform Traffic Control Devices as an alternative option to the circular green (CG). However, as implementation of the FYA permissive indication proceeds, there will be two permissive indications for practitioners to consider at protected–permissive left-turn applications. Using two signal indications that provide drivers with the same message has the potential to increase driver error. Specifically, once drivers are exposed to and understand the meaning of the FYA, it is unclear as to expectancy violations and the likelihood of incorrect interpretation of the CG as a protected left-turn indication. This research employed a multifaceted behavioral experiment, including a dynamic driving simulator experiment and computer-based static evaluations, to quantify any change in driver comprehension of CG indications resulting from the FYA permissive indication. In the simulator, comprehension of the CG permissive indication following exposure to the FYA permissive indication did not differ significantly from driver comprehension of the CG before exposure to the FYA. In a follow-up static evaluation, drivers exposed to the FYA permissive indication were actually more likely to give yield (correct) responses to the CG permissive indication. In a separate independent static evaluation of 100 drivers, the breakdown of responses did not differ statistically from responses collected before and after exposure to the FYA. Results provide little evidence to suggest that the FYA implementation will affect driver comprehension of the CG.

Analysis of Driver and Pedestrian Comprehension of Requirements for Permissive Left-Turn Applications

Operations engineers commonly program traffic signal controllers to serve the pedestrian movement at the same time as the parallel vehicular-through movement. This requires drivers completing a permissive left-turn movement to yield to opposing vehicles and pedestrians before selecting an appropriate gap. To minimize the potential safety problem, it is critical that drivers and pedestrians understand the permissive left-turn signal indications. The recently completed NCHRP Report 493 identified that a flashing yellow arrow (FYA) permissive indication provided a preferred alternative to the existing circular green permissive indication and recommended that the FYA permissive indication be included in the Manual on Uniform Traffic Control Devices. This paper presents research findings of a follow-up study that targeted the FYA impact on pedestrians, including driver comprehension of the need to yield to pedestrians and pedestrians’ recognition of appropriate crossing opportunities. Driver and pedestrian comprehension of the FYA indication was evaluated with a series of dynamic driving simulator evaluations and computer-based static evaluations. In total, 139 drivers and 100 pedestrians were evaluated in 5,930 experimental scenarios. The FYA permissive indication can be safely and effectively used at intersections with pedestrian activities. Given the high level of comprehension to yield requirements, the FYA is a recommended indication at T-intersections where pedestrian crossings are prevalent. Fewer than half the pedestrians understood correct crossing procedures when pedestrian signal heads were not present, and pedestrian comprehension of the walking requirements under a flashing “don't walk” were quite low in all scenarios evaluated.

Potential Application of Flashing Yellow Arrow Permissive Indication in Separated Left-Turn Lanes

The consideration being given to the adoption of the flashing yellow arrow (FYA) permissive indication has led to a number of additional studies evaluating potential scenarios in which FYA may be effectively used. One potential scenario is in intersections with wide medians where the left-turn lane and the corresponding signals are separated from the adjacent through and right-turn lanes. Left-turn maneuvers at locations with wide medians typically operate with protected-only left-turn phasing and separate signal displays, as drivers cannot see the adjacent through movement signals; however, some transportation professionals have implemented a flashing red arrow (FRA) that requires drivers to first stop before accepting a gap in the opposing traffic stream. This research quantified driver comprehension of the FYA permissive indications compared with that of the FRA indication for use at locations with wide medians. The research used both driving simulator and static experiments with 264 drivers responding to 1,260 experimental scenarios. The results found that drivers understood the meaning of the FYA indication. Nevertheless, FYA was associated with fail–critical response errors in the driver's first exposure to the FYA indication. The large number of drivers who interpreted the FRA as a yield condition was consistent with that from previous evaluations and indicated an incorrect comprehension of the indication. At locations with wide medians where the use of protected-only left-turn phasing may not be desirable, the use of the FYA or FRA permissive indications should be used only after consideration of the safety and operational issues common to the initial implementation.

Analysis of Driver and Pedestrian Comprehension of Requirements for Permissive Left-Turn Applications

Operations engineers commonly program traffic signal controllers to serve the pedestrian movement at the same time as the parallel vehicular-through movement. This requires drivers completing a permissive left-turn movement to yield to opposing vehicles and pedestrians before selecting an appropriate gap. To minimize the potential safety problem, it is critical that drivers and pedestrians understand the permissive left-turn signal indications. The recently completed NCHRP Report 493 identified that a flashing yellow arrow (FYA) permissive indication provided a preferred alternative to the existing circular green permissive indication and recommended that the FYA permissive indication be included in the Manual on Uniform Traffic Control Devices. This paper presents research findings of a follow-up study that targeted the FYA impact on pedestrians, including driver comprehension of the need to yield to pedestrians and pedestrians' recognition of appropriate crossing opportunities. Driver and pedestrian com...

Potential Application of Flashing Yellow Arrow Permissive Indication in Separated Left-Turn Lanes

The consideration being given to the adoption of the flashing yellow arrow (FYA) permissive indication has led to a number of additional studies evaluating potential scenarios in which FYA may be effectively used. One potential scenario is in intersections with wide medians where the left-turn lane and the corresponding signals are separated from the adjacent through and right-turn lanes. Left-turn maneuvers at locations with wide medians typically operate with protected-only left-turn phasing and separate signal displays, as drivers cannot see the adjacent through movement signals; however, some transportation professionals have implemented a flashing red arrow (FRA) that requires drivers to first stop before accepting a gap in the opposing traffic stream. This research quantified driver comprehension of the FYA permissive indications compared with that of the FRA indication for use at locations with wide medians. The research used both driving simulator and static experiments with 264 drivers responding...

Evaluation of Flashing Yellow Arrow in Traffic Signal Displays with Simultaneous Permissive Indications

The results of a comprehensive study on protected and permissive left-turn (PPLT) operations showed that the flashing yellow arrow (FYA) indication was an acceptable and recommended application for permissive left turns. As documented in NCHRP Report 493, an FYA permissive indication was recommended for implementation in the FHWA Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Research findings suggested that the FYA be implemented in an exclusive four-section vertical signal display centered over the left-turn lane, which differs from the most common application of PPLT signal displays. Many traffic engineers currently use a five-section clustered-arrangement shared signal head to meet MUTCD requirements of two signal heads per major approach. FYA implementation in the five-section display would require an interim retrofit requiring the FYA to be displayed simultaneously with the through-movement circular green (CG), circular yellow, or circular red indication. This research evaluated driver comprehension of the retrofit display and the resulting simultaneous indications by using a dynamic driving simulator and computer-based static experiments. A comparison of seven permissive left-turn scenarios featuring the CG or FYA permissive indications, or both, was completed. In total, 264 drivers evaluated 3,457 permissive left-turn scenarios. Results showed that simultaneous indications in the retrofit display did not affect the drivers’ understanding of the permissive indications. The drivers demonstrated an understanding of the yield requirement with simultaneous indications (with a 65% to 89% correct responses), providing evidence to suggest that the simultaneous indications would be suitable as an interim display to ease FYA implementation.

Evaluation of Flashing Yellow Arrow in Traffic Signal Displays with Simultaneous Permissive Indications

The results of a comprehensive study on protected and permissive leftturn (PPLT) operations showed that the flashing yellow arrow (FYA) indication was an acceptable and recommended application for permissive left turns. As documented in NCHRP Report 493, an FYA permissive indication was recommended for implementation in the FHWA Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Research findings suggested that the FYA be implemented in an exclusive four-section vertical signal display centered over the left-turn lane, which differs from the most common application ofPPLT signal displays. Many traffic engineers currently use a five-section clustered-arrangement shared signal head to meet MUTCD requirements of two signal heads per major approach. FYA implementation in the five-section display would require an interim retrofit requiring the FYA to be displayed simultaneously with the through-movement circular green (CG), circular yellow, or circular red indication. This research eva...