Power outage at City Hall snarls morning commute

The city’s Transportation Department, located on the seventh floor of City Hall, regulates many of the signals, but when employees showed up at 6 a.m. yesterday, they were confronted with the power outage, preventing them from manually adjusting the signals for rush hour.

Of the 817 “signalized’’ intersections in Boston, 434 are connected to the Transportation Department’s main computer, allowing the department to adjust green light time depending on the flow of traffic and time of day. They could not do that yesterday, but Thomas J. Tinlin, the department’s commissioner, said complaints were minimal and public safety was never compromised.

“Although traffic was moving slower, at no time was safety jeopardized by the signals, which continued to operate,’’ Tinlin said. “It wasn’t as smooth as usual, but they were running.’’

The signals the department usually controls during rush hour at the intersection of State and Washington streets have 60 seconds of green light time. When the system is not operational and the control box located near the signal kicks in, that time is cut by 9 seconds. On-site control boxes regulate the city’s other 383 signalized intersections.

Brian J. McDermott, who lives in West Roxbury and has driven to work on Brookline Avenue to the Fenway for at least 10 years, said his commute was delayed at least 20 minutes as he tried to navigate the intersection of Brookline Avenue and Park Drive. “You could tell the whole backup was based on the timing of the light,’’ he said. “It’s one thing when there’s a breakdown or an emergency and getting to work is not as important as someone getting emergency services, but this was different. And if the difference was 9 seconds, it was pretty drastic.’’

Other commuters said they were left wondering whether there was a movie shoot or some emergency that tied up traffic, but it became apparent the signals were malfunctioning, because they allowed only a few cars to pass through intersections at a time.

The system allowing the Transportation Department to make adjustments came back online at 9:08, Tinlin said.

The outage at City Hall was an internal problem, not the result of a break in service from NStar, according to a spokeswoman for the power company.

Tinlin said he was unsure what caused the outage, which lasted from late Tuesday into yesterday morning.