"Base Plate" Design for In-Roadway Warning Light (IRWL) Systems
By Mike Harrison, CEO LightGuard Systems™, Inc.
Though the topic may seem mundane, the very success of In-Roadway Warning Light
(IRWL) Systems depended on the development of a foundation for the in-pavement signal light source - what we call the "Base Plate".
As holder of an Airline Transport Pilot license and having logged over 7,000 flight hours, I knew the vital importance of runway lighting. Also due to my military experience as an aircraft mechanic, I was very familiar with runway lighting from having worked on many a tarmac servicing planes. So when I came up with the concept of placing some type of lighting in the roadway, I knew that "runway" lighting was not going to be the ultimate choice for many reasons. From the very beginning, we chose to pursue a better path.
First of all, runway lighting was, and still is, very expensive. Another problem was that the size and depth of the in-pavement "cans" (part of the supporting structure) required a deep hole in the roadway, generally penetrating through the roadway and into the base rock. This would have been expensive to install due to the required materials and labor to execute properly. One city that did try this early on experienced a multitude of problems with the IRWL's literally "sinking" into the roadway and rendering the systems inoperative. Also, runway lights at the time tended to "collect" debris.
Furthermore, airport runway lights are typically bi-directional. We were mindful of the fact that we were mandated by the California Traffic Control Device Committee (CTCDC), an agency of the State of California, to design our system in such a way that would "not allow the pedestrians to view the lights" in the roadway, as this could "false sense of security". Bi-directional lights do not fulfill this requirement. One company that was not authorized for the CTCDC experimentation process did decide to offer a "runway" bi-directional signal light. This IRWL design option ignored the CTCDC mandate; see our August 2010 newsletter of for a fuller discussion of this issue.
Our concept was to keep the IRWL within the first "lift" of the asphalt; not to protrude below a depth of 2 inches if at all possible. This would leave the roadway intact, and would not weaken the road bed by protruding into the base rock. In fact, when properly installed, our base plates are actually stronger and more resistant to failure than the asphalt itself.
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