There were severe delays on the M25 anti-clockwise stretching back for 12 miles following emergency repairs at the Dartford Crossing.
A power surge damaged safety systems that had to be reset by engineers, according to Highways England.
Queues were back as far as J4 for Orpington and the jams also affected traffic at Woolwich and Blackwall.
The situation was made worse after the traffic lights broke down at J3 for the M20 and A20 at Swanley.
All the lights went out, causing queues on all approaches.
The roblems have now been resolved by delays are expected throughout this evening.