When a massive power failure swept parts of northwest Ohio earlier this month, four traffic signals along busy U.S. 20/23 in Perrysburg Township kept working even though the juice was off there for more than an hour.
That's because when the Ohio Department of Transportation replaced the stoplights during a widening project last year, it installed battery systems to provide backup power at the highway's intersections with Carronade Drive, Simmons Road, and two sets of I-75 interchange ramps.
“The signals functioned exactly as designed,” Joe Rutherford, an ODOT spokesman, said. “A dark intersection is a very dangerous intersection. We believe these battery back-ups will significantly improve safety.”
More are on the way. Seven signals on Airport Highway in Springfield Township, and nine on Central Avenue in Sylvania Township that the state is replacing this year, all will have battery backups. By June, six more on State Rt. 795 will be similarly equipped, Mr. Rutherford said.
The cost for equipment and installation is about $5,500 per intersection.
“We plan to expand the program as resources allow,” he said. “Over the next couple of years, we plan to add [batteries] to all state-maintained traffic signals in the area.”
Larry Gamble, Maumee's service director, said batteries may be included when the city upgrades some of its signals.
“It's probably a pretty good idea, especially considering what happened [Aug. 14],” Mr. Gamble said.
Toledo and several other suburbs are taking a more wait-and-see approach.
“We've been talking about it, kicking it around a little,” said Tom Kroma, who was Toledo's transportation commissioner before an Aug. 15 job change to code-compliance commissioner. There have been discussions about what to buy and how to decide where to put it, Mr. Kroma said.
But even if only a fraction of Toledo's 550 signalized intersections were to have batteries installed, Mr. Kroma said, the cost easily could run over $1 million. And history has shown that emerging technologies become less expensive and more reliable over time, so the city may be better served by waiting and learning from others' experience.
Service directors in Oregon and Perrysburg said that battery backups surely will be a consideration. Jeff Ballmer, Sylvania's service director, said any such installations would have to be justified by a cost-benefit analysis.
A key to installing backup batteries is the use of light-emitting diodes in the traffic signals. Traditional stoplights, with incandescent bulbs, consume too much electricity to make battery operation practical. But LED arrays, which look like rows of tiny, brilliant lights within each lamp, consume only one-fifth the energy incandescents do.
While LED hardware is more expensive than incandescent bulbs, ODOT's savings on its electricity bill have been high enough to pay for the backup systems, Mr. Rutherford said.
Oregon, Maumee, Perrysburg, Sylvania, and Toledo have all, to varying degrees, begun retrofitting signals for LED use or replacing them entirely.
The backup systems ODOT is using do more than just provide emergency power, Mr. Rutherford said. They regulate power flow to traffic signals.
Before the Aug. 14 blackout, Mr. Rutherford said, there were six power “events” at the Carronade and Simmons intersections that left those signals without outside electricity for a combined 3.4 hours. The intersection at the northbound I-75 ramps had nine “events” while its southbound counterpart had two, he said.
“That area seems to have a lot of power outages,” the ODOT spokesman said.
The batteries provide more than eight hours of operation, which Mr. Gamble said would provide ample time during an extended outage for post-blackout traffic to clear and for city crews to post temporary stop signs where needed.
Granger Morgan, co-director of the Electricity Industry Center at Carnegie Mellon University in Pittsburgh, said signal backups probably could be designed to power signals for several days but agreed that the most critical time is when a blackout begins.
“An outage immediately snarls traffic, and you can't get emergency vehicles through,” Professor Morgan said. “The first few hours are what matter the most.”
The professor, who also heads Carnegie Mellon's department of engineering and public policy, said he has “been arguing for some while” that backup power sources should be in place not only for traffic signals, but also for water-main pumps and electric transit.
Batteries for traffic signals should be relatively simple, he said, but cash-strapped cities are hesitant to pay for what might be considered a luxury most of the time.
“You could view this as homeland security,” Professor Morgan said. “This might be a reasonable candidate for some federal dollars.”