New RRFB WW+S Flash Pattern (IMSA Jan/Feb ’15)

By Susan Marshall Electrotechnics Corporation (ELTEC)

On July 25, 2014 the FHWA approved a “new and improved” flash pattern for RRFB (Rectangular Rapid Flashing Beacons) uncon-trolled pedestrian crossings.

The new flash pattern is based on a flash cycle length of 800 milliseconds (ms) equaling 75 flash cycles per minute. It’s referenced as “WW+S” (Wig-Wag plus Simultaneous). The sequence is:

• Left beacon ON 50 ms Both beacons OFF 50 ms
• Right beacon ON 50 ms Both beacons OFF 50 ms
• Left beacon ON 50 ms Both beacons OFF 50 ms
• Right beacon ON 50 ms Both beacons OFF 50 ms
• Both beacons ON 50 ms Both beacons OFF 50 ms
• Both beacons ON 50 ms Both beacons OFF 250 ms

The interpretation was issued after the Texas Transportation Institute (TTI) tested several flash patterns for their effectiveness. Two patterns were found to be equally effective, but to keep some “uniformity” the “simpler” WW+S flash sequence was approved. Additionally, the WW+S was chosen “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 FHWA continued “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.”

Any newly installed RRFB pedestrian crossings may use either the currently approved flash pattern (2/4-1) or the WW+S. Existing RRFB systems may continue to use the installed flash pattern, or can be converted to the WW+S flash pattern.

For more information on the published TTI study go to: TTI Website. Clarification of interpretations can be found here at MUTCD link.