Question:  My City has a traffic signal with a protected left turn that is to be converted to a permissive.  There is a mast arm for this move which currently has a signal heads for the left turn phase and through phase.  I have been told there is a product available from Pelco called the Astro-Brac that I can use to replace both the existing heads with one doghouse head, and mount it in between the current head locations.  What more can you tell me? 

Answer:  Pelco has a product called AB-0109 Five Section Cluster Cable Mount Assembly that looks like what you need (see below).  You can also see it in their on-line catalog at http://www.pelcoinc.com/Portals/0/PDFs/T1-2-Way%20&%20Cluster%20Arm%20Kits.pdf or http://www.pelcoinc.com/Catalog/tabid/68/Type/2/Cat/10/Default.aspx.  You will still have to evaluate the traffic signal arm loading (weight and wind loading) to be sure you are confident with this modification.