Key train lines running through south London were blocked on Friday morning after a vehicle struck a bridge in Thornton Heath.
The crash means all lines in the area have been closed while emergency repairs are carried out.It is resulting in severe disruption to Gatwick Express services and Southern services between London and the south coast.
Meanwhile motorists are being warned of serious congestion ahead of an unprecedented weekend closure of a section of the M25.
The motorway will be shut in both directions between junctions 10 and 11 in Surrey from 9pm on Friday until 6am on Monday.
