Following an inspection of the bridge after a strike, the damage was found to the parapet 15 metres after the Roundhill Tunnel, explains the National Highways.
Therefore, a temporary varioguard barrier through the length of the tunnel was installed overnight on Thursday.
For safety, the London-bound A20 lanes through the tunnel have been reduced to one until repairs are completed.
When the tunnel is closed, eastbound diversions will be in place via A259 and A268 – drivers should follow the circle. Westbound diversions will be in place via the A268 and A259 – drivers should follow the square, the motorway operator adds.
Photo credits @ N Chadwick and licensed for reuse under C BY-SA 2.0