On Sept. 25, a failed electrical circuit cut power to Metro-North's busy New Haven line, forcing the agency to reduce rail service by half.
On Monday, the rail line returned to a full schedule of trains into Grand Central Terminal, thanks to a new electrical substation that had been activated at Mount Vernon, N.Y.
"We're good. We're back go full strength. No issues this morning," Metro-North spokesman Aaron Donovan said.
The return to normal should bring relief to Interstate 95, the Merritt Parkway and other highways in southwest Connecticut that were choked with commuters seeking alternative routes into New York.
Metro-North is refunding ticket holders who were unable to get train service during the 12-day outage.
Tens of thousands of commuters had to make other arrangements as the railroad tried to get by with a handful of diesel-powered trains, and then limited electric train service.
And Amtrak, which runs along the same corridor, advised passengers soon after the disruption that service in the Northeast would be significantly delayed. Acela Express service was suspended between New York and Boston, and service between New York and Washington was delayed.
The problem began when a Con Edison feeder-cable failure occurred during the construction of a $50 million substation intended to enable the railroad to increase service, Metro-North said.