develop safety performance functions (for left-turn as well as total number of crashes). The estimated number of left-turn and total number of crashes, had FYA signals not been installed, were then compared to the actual number of left-turn and total number crashes that occurred at the study intersections.Negative Binomial (log-link) distribution was observed to be a better fit to develop safety performance functions than Poisson (log-link) distribution. The results obtained indicate that FYA signals, in general, help reduce left-turn crashes (direct effect) as well as the total number of crashes (indirect effect) and contribute to improved safety at signalized intersections. They do not seem to be suitable for intersections with heavy-traffic volume.
This study evaluated the safety effect of the flashing yellow arrow (FYA) treatment at signalized intersections. The major objective of this strategy is to reduce the frequency of left-turn (LT) crashes, especially those that involve a collision between left turns and vehicles traveling straight through from the opposite direction. The project team conducted an empirical Bayes before-after analysis of installations in Nevada, North Carolina, Oklahoma, and Oregon. The treatments were divided into seven categories depending on the phasing system in the before and after periods, number of roads where FYAs were implemented, and number of legs at each intersection. The first five categories involved permissive or protected-permissive phasing in the before period. Intersections in these five treatment categories experienced a reduction in the primary target crashes under consideration: LT crashes and left-turn-with-opposing-through (LTOT) crashes at the intersection level. The reduction ranged from 15 to 50 percent depending on the treatment category. Intersections in categories 6 and 7 had at least one protected LT phase in the before period, and after phasing had an FYA protected-permissive LT phase without time-of-day operation (category 6) and with time-of-day operation (category 7). Consistent with results from previous studies, these intersections experienced an increase in LT and LTOT crashes. The B/C ratios for categories 1-5 ranged from 56:1 to 144:1.
This thesis evaluated the effectiveness of flashing yellow arrow (FYA) permitted left-turn signals in reducing conflicts and events at intersections. A FYA permissive signal is a recent treatment used as an alternate to circular green signal at signalized intersections. It is the newest addition to the series of permitted left-turn signal indicators and has been designed to improve the clarity of indication among drivers. The signal is expected to result in safer turning movements during the permitted phase. Conflict data was collected during morning peak period (7:00 AM to 9:00 AM) and evening peak period (4:00 PM to 8:00 PM) at four study intersections in Charlotte. Data was collected before the installation of FYA signal was introduced and after one month, three months and six months of installation of FYA. Relevant types of conflicts and events associated with left-turn maneuver were observed and recorded. Descriptive statistics, proportions of conflicts/events and statistical tests were conducted to analyze the data collected. Conflicts and events were also analyzed separately for each intersection using various comparison sets to understand their trend over time and the impact of FYA on them. Observations and analysis indicated that benefits in terms of reduction in conflicts and events are substantial at 7th Street / 5th Street intersection and Mallard Creek Church Road / 1-85 Southbound interchange but are marginal and currently statistically insignificant at Sunset Road / 1-77 interchanges. Overall, FYA leaves a positive effect on the intersection safety, helps reduce vehicular conflicts/events and is suitable for application at other intersections in the future.
This study evaluated the safety effect of the flashing yellow arrow (FYA) treatment at signalized intersections. The major objective of this strategy is to reduce the frequency of left-turn (LT) crashes, especially those that involve a collision between and vehicles traveling straight through from the opposite direction.--Abstract.
Selection of the left-turn phasing mode is a significant decision for the safe and efficient movement of left-turning traffic at signalized intersections. Because of different safety and operational effects associated with the signal left-turn mode, the two must be evaluated concurrently and be balanced based on capacity and crash potential when protected-only, permissive-only, and protected-permissive left-turn (PPLT) phasing modes are compared. The choice between left-turn phasing modes can be made on a time-of-day basis so that changing traffic conditions are accommodated appropriately. The purpose of this study was to define guidance that field traffic engineers can use to select the appropriate left-turn mode based on prevailing traffic conditions by time of day. In particular, guidance on the use of PPLT or permissive-only with flashing yellow arrows (FYAs) to indicate permissive movements was of interest to the Virginia Department of Transportation (VDOT). Prior to the development of time-of-day guidance, the overall safety effects of converting between left-turn phase modes and indications (or displays) needed to be explored. The study examined the impact of converting from a circular “green ball” display for the permissive portion of PPLT phasing to the FYA signal indication and converting from protected-only phasing to PPLT with FYA. To quantify these conversions, a before-after evaluation of signal conversions was performed using standard Bayesian methods to develop crash modification factors from field data for 28 intersections in Virginia. For these intersections, the expected crash reduction after conversion from PPLT to PPLT-FYA was estimated as 12 percent (total crashes), 14 percent (fatal and injury crashes), and 30 percent (angle crashes), which was consistent with results from previous studies. In evaluating different left-turn phasing modes on a time-of-day basis, crash risk, left-turn conflicts, and capacity prediction models for permissive-only and PPLT modes were developed using simulation data. A total of 750 unique scenarios based on different combinations of intersection characteristics, traffic signal parameters, and traffic volumes were simulated in VISSIM, and trajectory files were processed using Surrogate Safety Assessment Model software to determine the number of conflicts per scenario. Based on the outputs of the simulation models, prediction models for determining left-turn capacities and the expected number of left-turn conflicts per hour per 100 left-turning vehicles were created using multiple linear regression. A final model predicting the average crash risk per hour based on the predicted number of conflicts was developed. The three models created were incorporated into a single spreadsheet tool that can be used by VDOT engineers in determining phasing mode on a time-of-day basis.
In some jurisdictions, protected left-turn phasing has been replaced with the flashing yellow arrow (FYA) for protected/permissive left turns (PPLTs) to reduce delay. However, it is important to have a thorough understanding of the conflict between pedestrians and the permissive left-turning vehicle. This presentation summarizes the results of research conducted with a high-fidelity, motion-based driving simulator and mobile eye-tracking equipment to study the effects of the opposing traffic, the presence and walking direction of pedestrians, and the number of section heads to display the FYA on driver performance. To accomplish this research, a six-intersection simulated environment was created. In total, 27 subjects completed the course, allowing the analysis of 620 permissive left-turn maneuvers. Eye-glance durations for the intersection approach and turning maneuver were captured for left-turn pavement bay markings, the signal indication, the pedestrian and vehicle waiting area, and the pedestrian signal heads. The total glance durations for each of these areas were analyzed. The following results were obtained: 1) the increased presence of pedestrians led drivers to focus more attention on these crossing pedestrians; 2) as the number of opposing vehicles increased, drivers spent less time fixating on pedestrians; 3) Four to seven percent of drivers did not focus on pedestrians in the crosswalk; and 4) there did not appear to be a difference between any variable and the presence of a three- or four-section head. In terms of practice, the results suggest that it may be desirable to limit the permissive operation when pedestrians are present. Moreover, the findings may indicate that the additional cost of four-section heads is not justified.
This document is a technical summary of the Federal Highway Administration report Safety Evaluation of Flashing Yellow Arrows at Signalized Intersections (FHWA-HRT-19-036). This study investigated the safety effectiveness of the flashing yellow arrow (FYA) treatment at signalized intersections. One objective of this strategy was to reduce the frequency of left-turn (LT) crashes, especially those that involve a collision between left turns and vehicles traveling straight through from the opposite direction (also called left-turn opposite through (LTOT) crashes). Many studies have explored the safety effectiveness of FYAs. However, most of them only used data from one State, and the studies that used data from multiple States had limited samples of intersections. It is clear that an evaluation with a large sample of sites from multiple States would provide useful information to practitioners on the effectiveness of this treatment under different circumstances.
At signalized intersections, pedestrians are considered to be amongst the most vulnerable. When in the crosswalk at intersections without protected left-turn phasing, pedestrians are particularly at risk from left-turning vehicles. Until recently, a wide variety of indications were in use across the US to indicate a permissive left-turn condition to the driver. In Oregon, the Flashing Yellow Arrow (FYA) has been used to indicate the permissive left-turn condition for approximately 10 years. With the addition of the FYA in the 2009 MUTCD, it is likely that its use will continue to increase nationally. Though many operational and safety issues have been studied about the FYA indication, this research proposes to fully investigate factors that influence driver behavior in the context of the permissive left-turn conflict with pedestrians. Specifically, the research seeks to study driver glance behavior to identify reasons why drivers are, "looking at but not seeing" pedestrians in or near the crosswalk or not searching for the presence of pedestrians at all.
TRB National Cooperative Highway Research Program (NCHRP) Report 731: Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections offers guidance for yellow change and all-red clearance intervals at signalized intersections. The guidelines provide a framework that can be easily applied by state and local transportation agencies.
