So i recently jumped on the on-call rotation at work and so i now see and do things i wouldnt normally do. For example i just got called out to a Meter pedastol that was hit by a car that powers the traffic signals. The power company came out and cut the power.
I found out from the signal guys that the backup power supply last between 4-8 hours and will run like normal unless set to flash red to save battery life while they work on it. So just a little FYI on how long you can expect some what safe driving conditions in a total black out. After the batteries die all the signals go blank. Seeing normally running lights dosent mean they have a good power supply. If everythings dead they too will likely be dead in a few hours when the batteries die. No red flashing required.