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Publication Number:  FHWA-HRT-16-040    Date:  July 2016
Publication Number: FHWA-HRT-16-040
Date: July 2016


Evaluation of Pedestrian Hybrid Beacons and Rapid Flashing Beacons


Efforts during the initial phase of this project included literature reviews of selected pedestrian treatments as needed to build upon a previous FHWA study.(5) The previous FHWA study contains a comprehensive literature review of pedestrian treatments being used at unsignalized pedestrian crossings, and readers are encouraged to review that report if a review of the literature is sought. This chapter provides background information on the RRFB and a review of recently published literature that is relevant to the efforts within this project.


On July 16, 2008, FHWA provided IA-11 for the optional use of the RRFB.(4) FHWA approved the use of this device at uncontrolled pedestrian and school crosswalks. As defined in IA-11, the RRFB is to consist of two rapidly and alternately flashing rectangular yellow indicators having LED-array based pulsing light sources.(4) Within the IA-11, there are the following seven items with subsections:

  1. General conditions.

  2. Allowable uses.

  3. Sign/beacon assembly locations.

  4. Beacon dimensions and placement in sign assembly.

  5. Beacon flashing requirements.

  6. Beacon operations.

  7. Other.


As of November 2015, FHWA has released several official interpretations concerning the interim approval of RRFBs, including the following:

Another interpretation letter that may be of interest is 4(09)-11 (I) on flashing beacons maximum mounting height, which was released on June 29, 2011.(14)

Table 1 summarizes key components for each of the official interpretations released prior to 2014. Table 2 summarizes the interpretations that were developed using results from this FHWA research study.

Table 1. Summary of RRFB official interpretations released prior to 2014.
Number Summary of Key Characteristics Relevant to this Study
4-376 (I)(6) Interpretation letter 4-376 (I) indicates that overhead mounting of the pedestrian crossing (W11-2) warning sign or school crossing (S1-1) warning sign with a RRFB is appropriate. When the W11-2 or S1-1 sign is mounted overhead, only a minimum of one such sign per approach is required, and it should be located over the approximate center of the lanes of the approach. It also indicates that "for roadside signs, the MUTCD establishes no maximum mounting height. Therefore, W11-2 or S1-1 signs with W16-7P plaques could be installed at a mounting height much higher than the normal 7 feet, perhaps 15 to 17 feet or more, and still comply with the MUTCD and the IA-11 technical provisions."(6)(pg. 2)
4(09)-5 (I)(7) Interpretation letter 4(09)-5 (I) states that the "RRFB may be used to supplement a W11-15 sign at a shared-use trail crossing if the W11-15 substitutes for the W11-2 and is placed at the crosswalk."(7)(pg. 1)
4(09)-11 (I)(14) Interpretation letter 4(09)-11 (I) states that "the maximum mounting height of a flashing warning beacon mounted over the roadway shall be 25.6 ft, measured from pavement surface to the top of the housing of the beacon."(14)(pg. 1)
4(09)-17 (I)(8) Official interpretation number 4(09)-17 (I) clarifies that the light intensity of RRFBs shall meet the minimum intensity requirements for class 1 optical warning devices within SAE Standard J595, as opposed to classes 2 or 3 minimum intensity requirements.(15) The SAE J595 peak luminous intensity requirements for classes 2 and 3 are only about 25 and 10 percent, respectively, of the peak luminous intensity requirement for class 1.(15)
4(09)-21 (I)(9) A detailed review of the flash pattern used with the original RRFB installation resulted in a change in the requirements. Official interpretation 4(09)-21 (I) changes item 5b to read, "b. As a specific exception to 2003 MUTCD Section 4k.01 requirements for the flash rate of beacons, RRFBs shall use a much faster flash rate. Each of the two yellow indication of an RRFB shall have 70 to 80 periods of flashing per minute and shall have alternating, but approximately equal, periods of rapid pulsing light emissions and dark operation. During each of its 70 to 80 flashing periods per minute, the yellow indication on the left side of the RRFB shall emit two slow pulses of light after which the yellow indication on the right side of the RRFB shall emit four rapid pulses of light followed by a long pulse."(9)(pg. 2)
4(09)-22 (I)(10) Official interpretation 4(09)-22 (I) clarifies that agencies do not have to update the flash pattern for devices already deployed in the field and that official interpretation 4(09)-21 (I) only applies to new deployments.
4(09)-24 (I)(11) Official interpretation 4(09)-24 (I) states that "it is not acceptable to dim the RRFB signal indications during daytime conditions and that the light output from the RRFB signal indications must meet the SAE J595 requirements for peak luminous intensity (candelas) for Class 1 at all times during daylight hours."(11)(pg. 1) Information on SAE J595 is available in Surface Vehicle Recommended Practice.(15)
4(09)-37 (I)(12) Official interpretation 4(09)-37 (I) states that "It is the FHWA's official interpretation that dimming occurs only when the light output from a traffic control signal indication or an RRFB signal indication falls below the minimum specified intensity for daytime conditions."(12)(pg. 1)
4(09)-38 (I)(13) Official interpretation 4(09)-38 (I) states that "It is the FHWA's official interpretation that the predetermined flash period should be initiated each and every time that a pedestrian is detected either through passive detection or as a result of a pedestrian pressing a pushbutton detector. This would include pedestrians who are detected while the RRFBs are already flashing and who are detected immediately after the RRFBs have ceased flashing."(13)(pg. 1)
Table 2. Summary of RRFB official interpretation developed using the results of this research project.
Number Summary of Key Characteristics Relevant to this Study
4(09)-41(2) Official interpretation 4(09)-41 (I) states that, "...the FHWA favors the WW+S (wig-wag plus simultaneous) flash pattern because it has a greater percentage of dark time when both beacons of the RRFB are off and because the beacons are on for less total time. The greater percentage of dark time is important because this will make it easier for drivers to read the sign and to see the waiting pedestrian, especially under nighttime conditions. The less total on time will make the RRFB more energy efficient, which is important since they are usually powered by solar energy."(2)(pg. 1)
4(09)-58 (I)(3) Official interpretation 4(09)-58 (I) states that, "...it is the FHWA's official interpretation that any new RRFB units that are installed under the terms of Interim Approval 11 may be placed either above or below the crossing warning sign. Existing RRFB units that are placed below the crossing warning sign may be retained in their current position or may be relocated to be above the sign."(3)(pg. 1)


RRFBs flash in an eye-catching sequence to draw drivers' attention to the sign and the need to yield to a waiting pedestrian. It may be located on the side of the road below the pedestrian crosswalk or school crossing signs or overhead with a sign and can be activated actively (pushing a button) or passively (detected by sensors) by pedestrians. Several studies have examined the effectiveness of the device or elements contained within the device, including the following:

All of these studies used a before (none or continuously flashing beacon treatment) to after (RRFB installed) design and found an improvement in driver yielding after the RRFBs were installed. (See references 16–22.)

Other studies focused on examining how different features of the rapid-flashing beacons affect driver yielding. A study of two sites in Santa Monica, CA, compared the effect of an RRFB and a circular rapid-flashing beacon (CRFB) on yielding behavior at two crossings.(23) The RRFB was installed at one site, and the CRFB was installed at the other. After an evaluation period, they were switched and evaluated again. The study evaluated driver yielding rates both when the beacons were actuated and when they were not actuated. In all cases, driver yielding rates were higher when the beacons were activated.

An FHWA study also investigated differences between RRFBs and CRFBs.(5,24) Both were installed at 12 sites located in 4 cities. The statistical results indicated that there were no significant differences between the two beacon shapes.

For a subset of the 12 sites used in the FHWA study to evaluate the beacon shape, the luminous intensity (also called brightness) of the beacons was measured.(24) For those sites, there was evidence of an increasing yielding rate with increasing intensity at night.

Additional research was done at those 12 sites to evaluate the effect of the activation of the beacons and traffic volumes on driver yielding behavior when a crossing pedestrian was present.(25) The results of the analysis suggest that when a beacon—whether rectangular or circular—was activated, a driver was 3.68 times more likely to yield to pedestrians than when it was not activated. The results of an analysis of the relationship between traffic volume and driver yielding suggested that driver yielding behavior was not influenced by traffic volume at the study sites; however, the sample size available may have limited the ability to identify a relationship.


In a FHWA study, researchers conducted a before-after evaluation of the safety performance of the PHB.(26) Using an empirical Bayes method, the evaluations compared the crash prediction for the before period without the treatment to the observed crash frequency after installation of the treatment. To develop the datasets used in the evaluation, researchers counted the crashes occurring 3 years before and up to 3 years after the installation of the PHB. The crash categories examined in the study included total, severe, and pedestrian crashes. From the evaluation considering data for 21 treatment sites and 102 unsignalized intersections (reference group), the researchers found the following changes in crashes following installation of the PHBs:

In a 2006 study, drivers yielding at five PHBs (known as HAWK sites at the time of the study) had an average driver yielding value of 97 percent.(27,28) For the sites included in the study, the number of lanes (two, four, or six lanes) did not affect performance. The driver yielding was very high compared to the other pedestrian devices included for the speed limits (either 35 or 40 mi/h) and intersection configurations (four-legged, T, offset T, or midblock crossings) represented in the dataset.

PHBs generally rest in a dark mode. A concern has been expressed that drivers may believe there is a power outage present and that the device is malfunctioning due to its dark resting mode, resulting in the need to come to a complete stop at the crossing. A study of driver behavior in Tucson, AZ, which had over 60 PHBs installed at the time of the study, investigated this concern and did not find evidence of confusion.(29) Driver perception of PHBs was studied in Kansas to identify drivers' knowledge of each phase of the device.(30) Surveys were distributed to drivers in stopped vehicles at a midblock PHB crossing and at a nearby signalized intersection. The results of the survey showed that drivers understood the dark (94 percent) and steady red (91 percent) signals well, understood the flashing yellow (76 percent) and steady yellow signals (67 percent) moderately well, and had poor understanding of the flashing red signal (58 percent).

A study in Oregon was conducted where three 1-h visits were made to a PHB site.(31) Compliance was observed to be very high; however, no records were made. They noted that drivers of queued vehicles sometimes proceeded through the crossing when the beacons changed to flashing red "without checking to see if the crossing was clear."(31)(pg. 67) Additionally, a 2014 Vermont study reported on a site near a hospital where, following installation of the PHB, yielding compliance increased by 18 percent, and there was an 83 percent increase in the number of vehicles slowing as they approached within 300 ft of the crosswalk.(32) PHB installation in San Antonio, TX, resulted in driver yielding increasing from 0 (i.e., no drivers yielding to staged pedestrians in 39 crossing attempts) to 95 percent for 60 staged pedestrian crossings.(33) All of the non-staged pedestrians at this site activated the treatment. An increase in the number of non-staged pedestrian crossings was observed after the PHB was installed. Finally, a study of three PHB installations in Charlotte, NC, found an increase in the number of motorists yielding to pedestrians.(34) Because data were collected for several periods after installation, they were able to conclude that improvements seemed to be relatively more consistent 3 mo after the installation of the PHB. In other words, it may take 3 mo for pedestrians and motorists to adapt to the new device.


A Texas Department of Transportation study explored the factors associated with drivers yielding to pedestrian crossings with traffic control signals (TCSs), PHBs, and RRFBs in Texas.(35,36) The percentage of drivers who yielded to a staged pedestrian was collected at 7 TCS sites, 22 RRFB sites, and 32 PHB sites. Overall, TCSs in Texas had the highest driver yielding rates, with an average of 98 percent. The average driver yielding for RRFB in Texas was 86 percent, while the average for PHB was 96 percent. All of the RRFB sites had school crossing (S1-1) signs. The number of devices within a city may have an impact on driver yielding. Those cities with a greater number of a particular device (i.e., Austin, TX, for the PHB and Garland, TX, for the RRFB) had higher driver yielding rates as compared to cities where the device was only used at a few crossings. Comparing the number of days since installation revealed statistically significant higher driver yielding rates for those PHBs that had been installed longer. The authors concluded that based on the statistical evaluation of the 32 PHB sites, the results support the use of the PHB on roadways with multiple lanes or a wide crossing. For RRFBs, the posted speed limit, total crossing distance, one-way versus two-way traffic, and location were all statistically significant. The data revealed a trend of lower driver yielding rates for wider crossing distances as compared to shorter crossing distances. This finding indicates that there is a crossing distance width where a device other than the RRFB should be considered.



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