Rectangular rapid flashing beacons (RRFBs) have gained a lot of popularity in the last few years since the FHWA and Caltrans granted what is called Interim Approval of the device.  Unfortulately, FHWA recently withdrew approval, and within the last month Caltrans followed suit.  It seems one vendor of the product obtained a patent for the central part of the technology, and FHWA does not endorse products that are patented.   

W-Trans has been following posts on the ITE discussion board and has also reviewed recommendations from several vendors who have been selling RRFB systems, and it appears a consensus may be emerging on how to move forward.  The option is not finalized, but appears to include use of a pedestrian sign with LED lights around the edges, coupled with a single 12" yellow beacon in place of the dual rectangular beacons.  For more discussion, see https://www.linkedin.com/feed/update/urn:li:activity:6359924015745818624/