December 20, 2014
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Burnt out
Spotty traffic signals show their age, but LED savings keep adding up
John Howell
GOING AND GOING: While individual diodes are dying after more than five years, LED traffic signals like these keep on operating.

Some look more like gun targets than traffic lights, but the state Department of Transportation says even though they were 75 times more expensive than their predecessor, they annually save the state about $1 million.

The traffic signals are LEDs, or light emitting diodes, that after six and seven years of flashing off and on are starting to die out. As the lights are made up of multiple diodes, some diodes have expired, giving the signals their pockmarked appearance. Not all the older lights demonstrate the same characteristics, just those from a manufacturer that did not incorporate a diffuser lens, says Robert Rocchio, manager of DOT traffic engineering. While lights with the diffuser are also made up of multiple diodes, they appear to fade before going out totally.

However, while the lights eventually reach the point where they need to be replaced, there’s no question they have been a good deal for the state. The experience with traffic signals now has DOT exploring the use of the technology for overhead street lighting.

“Now the next big change is in highway lighting,” Rocchio said.

He said the department is working on a proposal to replace 400-watt high-pressure sodium (HPS) lights on Route 95 between Exits 1 and 4 with 200-watt LEDs.

Like the traffic signals, LED street lights are exponentially more costly than HPS lights. Rocchio said HPS’s cost about $200, whereas the LED replacement is about $1,000. Rocchio said overhead LEDs that produce a whiter light and do not give the orange glow of an aging HPS are being used in parts of Texas and California but, so far, not in the Northeast. He said DOT would seek grants to fund a pilot program for the Route 95 project of 100 lights.

Even without changing lights on the interstate highways, the DOT is generating $600,000 in savings by turning them off. More than a year ago, the department introduced a system of turning off lights after midnight from Exits 1 through 8 on Route 95 from Sunday to Thursday and after 2 a.m. Friday and Saturday. Retrofitting signs and road stripes with greater reflective materials preceded the program.

The department imagined they would get complaints about the reduced lighting, but to the contrary, they received compliments from people who were pleased by the reduction in ambient lighting. Further, experience has shown no increase in accidents from the absence of lighting in these less traveled sections of highway.

As the DOT discovered with traffic signals, LEDs make up for more than their added expense in reduced electrical and maintenance costs. The LED’s longer life – a traffic signal bulb is warranted for five years although, as the DOT is discovering, can last many more years – outshines its incandescent predecessor that died after six months. Incandescent 116-watt bulbs cost $2 each as compared to the 12-watt LEDs at $150. The reduced wattage of the state’s 800 traffic signals, Rocchio estimates, saves $1 million in electrical costs.

That's just part of the picture. With the lights' longer lives, DOT crews aren't spending as much time replacing bulbs that requires a special detail officer to route traffic while the intersection is inoperative.

While LED traffic signals generate savings, they are no less susceptible to lightning than their cousins. Despite efforts to ground the lights, Rocchio said in storms like the one that hit last Wednesday, the state will lose two to three lights. The lightning strikes do not only knock out the bulbs but generally "fry" the signal’s computer as well. The department has looked at concrete poles, as used in areas with frequent electrical storms such as Florida, but not found a replacement program practical.

Signals that require a massive foundation, trenching for road sensors and the devise with its computer components cost about $100,000.

As for the LEDs that are going out as they age, Rocchio said they are being replaced. And while the individual cost of the bulbs hasn't changed significantly, there's a trade-in value to the old bulbs – about $75 each – that just means more savings to the state.


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