Lessons learned from installing LED traffic signals: ten years later

Jeff Ramsey, P.E.

City Engineer/Director of Public Works City of Auburn, Alabama Member, APWA Transportation Committee

oes changing from incandescent bulbs in traffic signals to LED lamps actually save money? We did an assessment and to our surprise, the switch saved us even more than we had anticipated. The combination of maintenance and energy cost savings resulted in a payback period of four years, which was a full three years shorter than we had estimated.

In early 2003, the City of Auburn replaced all of the incandescent bulbs in our 48 traffic signals with Light Emitting Diodes (LED). At that time not many cities had switched from incandescent bulbs to LED lamps. As engineers we are cautious about trying new technologies. We like to allow others to discover the shortcomings of the technology so we can minimize failures. The energy cost savings realized by replacing the incandescent bulbs and the longer life of the LED lamps were the main reasons we decided to make the change.

Traffic signals traditionally required 150-watt bulbs to provide the illumination necessary to meet the federal guidelines. At a typical intersection we had 32 incandescent bulbs. At the time the average energy cost of operating an intersection was $966.48 annually. The new LED signal heads required only 14 watts of electricity to operate. We determined the typical LED intersection would cost $217.44 annually to operate. The project required replacement of 362 red balls, 358 green balls, 85 green arrows, and 61 red crosswalk signals. The expected savings in energy cost was determined to be $20,248.85 per year. Considering only the energy cost, it was estimated the project would pay for itself in 7.32 years. This analysis assumed no energy cost increase for seven years.

Another desired feature of the LED signals was the long life of the lamp. The typical life of the LED lamp was projected to be 10 years. We were changing an average of 15 incandescent bulbs per week at an average replacement cost of $20 per bulb. We estimated an expected annual savings of $15,600 on the cost of labor and materials needed to maintain the bulbs.

Combining the energy savings and labor and materials savings, we determined the project would pay for itself in 4.1 years, with a total savings of $358,488.

Usually when we speak of “unattended consequences” it is in a negative manner. However, in this situation the unattended consequences proved to be beneficial. Because of the lower power consumption, we were able to install an uninterrupted power supply (UPS) at all our intersections.

Previously, a typical intersection would draw 3,450 watts of power to run the signals. With the switch to LED lamps we are able to reduce the power drawn to 448 watts. The much lower wattage draw made it feasible to install a UPS that would run the intersection from two to four hours. The two-hours run time is more than enough time for most power outages. We are able to provide for a safer traffic flow during major weather events (when most power outages occur). Use of the UPS was not part of our discussion and analysis when making the decision to switch to LED, but it has been extremely beneficial to the City.

Another advantage of the UPS is cleaner power which has reduced the failure rate for controls and other circuit boards. Prior to use of the UPS we experienced power surges that damaged equipment and put signals in flash mode. Overtime call-outs have been reduced to almost none since we installed the LED and UPS systems. The reduced workload has allowed us to put off hiring additional staff, even as we continue to add new signals. We have been able to step up maintenance and rebuild older signals to minimize signal failures. Here again is another unattended consequence of switching to LED traffic signals.

I have heard from colleagues in northern states that icing of the lamps can be a problem in the winter. This is due to not enough heat being generated to keep the lens free of ice and snow. However, in Alabama this has not been a problem. We have now replaced all of the downtown streetlights with LED lamps and are hopeful of the same results as our transition to LED traffic signals.

Due to the positive outcome of our switching to LED lamps, the City of Auburn now uses LED lights exclusively, and the total savings are expected to be $89,622 annually. For more information on how you can make this switch, contact Jeff Ramsey, Public Works Director, at (334) 5013000 or jramsey@auburnalabama.org.