Volunteers were twice forced to direct high street traffic after temporary traffic lights failed.
The lights are part of ongoing roadworks by UK Power Networks in Highgate High Street.
But the signals, operated by tbf Traffic, suddenly both became stuck on red early last Wednesday evening, causing gridlock.
Residents and Highgate Society volunteers Jane Hill, Helen and Allan Rapley, Taha Gulamhusein, and Derek Proops sprang into action in high-vis jackets to keep traffic moving.
Highgate Society chair Andrew Sulston praised their "remarkable display of community spirit".
He said: "For two hours the team directed traffic to keep the High Street moving.
"Frustrated drivers showed their appreciation with thumbs-up as they passed by."
"A technician eventually arrived to recode the traffic lights, but two days later, on Friday evening, the traffic lights failed once again during a power cut.
This time, the northbound light stayed on red, while the southbound light remained green, leading to a massive tailback stretching down Highgate Hill.
"Yet again, the volunteers stepped in, donning their high-visibility jackets, and taking charge of the traffic management," Mr Sulston said.
"This coincided with a power cut on the east side of the High Street that affected the street lights, making the work more hazardous.
"Touchingly, UK Power Networks kindly offered to pay for a fish and chip supper for the volunteers."
The roadworks are due to be completed today (Wednesday). Mr Sulston added: "The episode serves as a reminder of the power of community action, but also of the need for reliable infrastructure management.
"Where public safety is concerned, traffic management should be fit for purpose. The community spirit was commendable, but volunteers should not be left to find solutions where critical infrastructure fails."
A spokesperson for UK Power Networks said: "Engineers have been working on Highgate High Street on essential works for a customer in the area.
"The works have been approved by the local authority and were timed to cause minimum inconvenience. We are sorry for the problems described and thank the volunteers who stepped in on site."
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