STC in the News

Gilbert, AZ adds to its solar-powered traffic equipment assets

TEMPE, AZ - 01/05/2014 - Gilbert, AZ, a suburb of Phoenix, recently purchased additional solar-powered traffic control devices for public safety. The city installed two solar-powered 9-inch Trafficalm driver feedback signs in a residential area as a pilot project to curb speeding.

The city looked at the options of using a 15-inch or a 9-inch sign and selected the 9-inch which works well on the 25mph posted street. The city has long been a leader in the state of Arizona with solar-powered traffic devices starting with the installation of four solar school beacons in 1999 which are still in use.

Solar Traffic Controls, the Trafficalm distributor in AZ, furnished the systems which included the signs themselves, spun aluminum pole kits and an STC SPAD030 solar power system. The size of the solar power system is based on the projected display time per day and is derived from the ADT for the street.

Any reasonable solar power system design looks at three factors: location, load and duty cycle. In the case of a radar sign the duty cycle can be highly variable and is directly related to the ADT on the street where the equipment will be installed. The higher the ADT the larger the solar array and battery bank must be to power the sign under worst case design assumptions since the sign will run longer each day. It should be noted that some manufacturers offer one-size-fits-all solutions. While these are lower cost one must consider that something has to give in the case of a higher ADT roadway and that is typically display intensity.

The city will track the performance of the project using the included data logging software. The Trafficalm 9-inch sign includes a 'stealth' mode in which it can log radar data but does not show a speed display to approaching vehicles.

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