Power has been restored inside the Lowry Hill Tunnel and lights on the westbound side are back on.
Lights illuminating the tube on the westbound lanes went out around 2:16 a.m. and came back on about six hours later.
During the outage, the Minnesota Department of Transportation was telling drivers to "use caution and turn on your headlights"
It's not immediately clear what led to the outage, a MnDOT spokesman said.
Over the past few nights, crews have been working in the tunnel to remove concrete curbs ahead of a larger project that will eventually shift all traffic to one side of the tunnel this summer.