Each year, more than 4 million traffic lights consume an estimated 3 billion kilowatt-hours of electricity. Switching to energy-efficient LED lamps trims municipal budgets and lowers energy use nationwide. More than 50 percent of all traffic signals have been converted to LEDs in the U.S., even in large cities like Boston, Denver, New York City, Philadelphia, San Diego and Seattle.
What are LED lamps and what are the benefits?
A light emitting diode is a tiny semiconductor that emits visible light when an electric current passes through it. Unlike ordinary incandescent bulbs, there is no filament. LED traffic signals use high-brightness LEDs connected together to build a cluster consisting of hundreds of LEDs.
LED lights only produce light in the desired colors, such as red, yellow or green, making them ideal for traffic signals. There is no need to filter the light through a lens. As a result, true colors are produced more efficiently, with minimal waste of heat energy. LED lights consume only 10 percent of the energy used by incandescent lamps (10-25 watts versus up to 150 watts, respectively). LED lights also look brighter since the light is distributed equally across the entire surface (an advantage in poor weather conditions).
LED lamps last 100,000 hours (fifty times longer than incandescent bulbs at 2,000 hours) because there are no filaments to burn out. Relamping cycles and emergency replacement projects decrease, reducing maintenance costs. This provides staff with more time for other projects.
LED lights also increase traffic safety as they minimize the number of signal outages and due to their low energy consumption, LEDs are more economical to use with battery back-up systems. Batteries can keep LED traffic signals functioning for up to 24 hours in the event of a power outage.
How much do LEDs cost and what are the potential savings?
Though LED’s have a higher purchase price, they save money in lifetime operating expenses. According to one study, the initial cost of a typical LED traffic signal ball was around $70 compared to an incandescent signal at $20. When energy use and maintenance costs were added, the total lifetime operating costs of LED lights were approximately one-third that of incandescent signals.
If a typical incandescent signal uses a 100-watt bulb and operates 24-hours per day, it will use 2.4-kilowatt hours (kWh) each day. Assuming a cost of 8 cents per kWh, the signal costs about 20 cents per day or $73 dollars per year to operate. An equivalent LED signal would consume about 10 watts, or approximately $7 dollars per year. Even a small city with a few dozen traffic signals could achieve significant energy savings.
Using LEDs instead of traditional bulbs can save up to $600 at a single intersection in one year (assuming eight signals); a single large city could save a million dollars or more, depending on how many intersections they have. Changing bulbs less often saves on labor costs, as well.
Red lights are on approximately 60 percent of the time or 5,300 hours per year, and use far more energy in a traffic signal than green or yellow lights. Often, they are larger with a higher wattage, as well. On average, red lights use 85 percent of the total energy consumed by a traffic signal. Replacing a red light, such as a 150-watt red incandescent directional arrow with a 10-watt LED lamp, can achieve the greatest energy savings. The following table compares the typical power consumption of LEDs to incandescents.
Comparison of Power Consumption, watts
|Solid Traffic Light||150||25|
|Red Directional Arrow||150||10|
|Pedestrian Hand Signal||75||12|
The following cities have achieved energy savings and reduced maintenance costs by installing LED traffic signals:
- Abington Township (Montgomery County, Pennsylvania) converted the incandescent lights in its 104 signaled intersections to LEDs. In total, over 2,500 lamps were retrofitted including red, green and yellow traffic signals and pedestrian signals. The payback was only three years at a total cost of $120,000, or roughly $50 per lamp replacement. The township saw a 90 percent reduction in energy costs for traffic signals, significantly less maintenance and positive responses from residents because of the brighter light that was emitted.
- With the installation of LED traffic lights at 2,900 intersections, Chicago is saving $2.55 million in energy costs and $100,000 in materials, annually. Carbon emissions have also been reduced by 23,000 tonnes. The total cost of the project was $32 million, which is being funded, in part, by city bond money. Complete battery backup systems were also installed at 800 traffic signal intersections to maintain operations during power outages.
- Maryland Transportation Authority is converting lane-use signals at the Bay Bridge, Harbor and Fort McHenry tunnels to LED-type signals to take advantage of their superior vibration resistance, resulting in less maintenance costs.
LED manufacturers continue to upgrade their products. One patented, integrated traffic signal is fully compatible with the wiring and mounting hardware of existing units, eliminating the need for the assembly of LED traffic signal modules in the field. The new unit consumes less than seven watts as compared to existing LED units, which consume up to 30 watts. A replaceable power supply allows users to convert to DC voltage for enhancing public safety.