LED traffic signal modules as an incandescent lamp alternative

Institute of Transportation Engineers. ITE Journal, Apr 2003 by Iwasaki, Randell H

THE CALIFORNIA DEPARTMENT OF TRANSPORTATION HAS BEEN INVOLVED WITH THE DEVELOPMENT Of LIGHT-EMITTING DIODE TRAFFIC SIGNAL MODULES FOR MORE THAN A DECADE. THIS INVOLVEMENT DID NOT GROW OUT OF THE RECENT ENERGY CRISIS, BUT THE CRISIS DID PLAY A KEY ROLE IN SPEEDING UP THE STATEWIDE CONVERSION FROM INCANDESCENT LIGHTS TO LEDS.

THE CALIFORNIA DEPARTMENT of Transportation (Caltrans) is one of the largest users of light-emitting diode (LED) traffic signal modules in the world. Since January 1998, Caltrans has purchased more than 230,000 units for deployment at signalized intersections, ramp meters and flashing beacons. This number does not include the 8,000 units deployed prior to 1998 in the Fresno and San Francisco Bay areas of California.

With the current deployments at signalized intersections and ramp meters, Caltrans has dropped its power demand by 10 megawatts and has reduced electrical consumption by 71 million kilowatthours per year. This translates to taxpayer savings of $10 million per year for the California state highway system alone. Caltrans operates about 10 percent of the traffic signals in California; therefore, the statewide energy savings are far greater if all traffic signals are converted. The availability of LED traffic signal modules led the California Energy Commission to introduce rules prohibiting the use of incandescent lamps for traffic signal indications on future traffic signal installations.

While some might think that Caltrans' involvement in LED traffic signal modules grew out of the energy crisis of 2000/2001, the LED program was up and running when the crisis struck the Golden State. The energy crisis did play a key role in speeding up the statewide conversion from incandescent lights to LEDs for Caltrans as part of a statewide effort to relieve pressure on the electrical grid. Prior to the crisis, the energy and maintenance savings for Caltrans were more than enough to justify the increased expense of LED modules. The energy crisis accelerated the rate of deployment by about three to four years. The rising cost for energy as a result of the crisis simply increased the economic viability of LED modules.

THE GROWTH OF AN IDEA

Caltrans is no stranger to LED technology. The department has been involved with the development of LED modules for more than 10 years. In that time, Caltrans has seen the performance of LED technology increase to the point that the department now has a full complement of LED modules at its disposal. In addition, energy requirements and prices for LED modules have decreased. Not using LED modules now is an unwise business practice.

Caltrans' involvement in LED traffic signal modules began in 1992, when the department's Fresno-area electrical crew supervisor, Gerald Tripp, came across a company with the idea to use LEDs to replace incandescent lamps in red indications. However, this was not a new idea. It was briefly discussed in Caltrans in the late 1980s, but LED technology at the time was not bright enough to meet traffic safety requirements. By the early 1990s, however, the major LED material, gallium phosphide, was becoming brighter and aluminum-gallium-arsenide (AlGaAs) technology was getting started.

A large eight-phase intersection in the city of Clovis, CA, (near Fresno) was the main reason Tripp looked into LED modules. The newly installed signal in operation at the intersection was too large and often overloaded the electrical system, causing constant signal malfunctions.

One option was to redesign the intersection to allow for the traffic signal, which would have been expensive and would have taken years to finish. Instead, Tripp initially installed eight LED pedestrian signals. This helped, but it was not enough. Tripp knew he needed to find a low-power lamp replacement for the red signals.

After talking with a local supplier, he replaced the red indications at the intersection with LED modules. The overloading problems disappeared. The current draw decreased from more than 50 amps to 14 amps. Tripp also found that energy usage for the intersection dropped significantly-more than anyone expected from simply replacing red indications. In addition, as one would expect, dollar amounts were greatly reduced because less energy was used.

Tripp and his supervisor, Jerry McElroy, began a mission to change traffic signal operations in California. Tripp suggested the idea to Caltrans management and was rewarded for his ingenuity and innovative style through the State of California Merit Award Program.

CALTRANS AND LED TECHNOLOGY

Caltrans started some test deployments in the Fresno area. In 1993, Caltrans' Resource Conservation Program funded the installation of the largest LED signal field test in the world at that time. More than 2,300 red signals were installed. Data collected from the test site helped the department develop LED signal performance specifications.

The trial proved that LEDs could operate in the traffic environment. It should be noted that the majority of problems encountered did not occur with the LEDs themselves; the power supplies and housing materials required many design improvements. The LEDs performed within the parameters stated by their manufacturers. During this time, the state and signal suppliers worked closely with LED manufacturers, other LED suppliers and industry partners to improve the product.