The Highways Agency said it decided to keep the Boston Manor Viaduct closed because during works it found a crack in a "sensitive location", which requires it to be kept closed until it is repaired.
Diversion on the A312 and the A4. Drivers are being advised to allow extra time for their journeys.
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The Ashford International to Canterbury West rail line should reopen on Thursday. It has been closed since a train derailed on Sunday.
Wednesday morning's weather for the east of the region
Wednesday morning's weather for the west of the region