Trains are expected to start running between Yeovil Junction and Exeter St Davids for the first time in five days this morning.
Operator South West Trains said it expects to restore a limited train service on the West of England line, which has been closed since last Wednesday due to flooding and a landslip.
Engineers had hoped to clear the line over the weekend, but more heavy rain on Saturday caused further damage.
From the start of the service today, a two-hourly train service will operate between London Waterloo and Exeter St Davids.
A separate two-hourly service will also operate between London Waterloo and Yeovil Junction.
Passengers are advised that journeys will take longer than usual as a result of speed restrictions in place on some sections of the track.
Trains are also expected to be very busy as other train operators in the region are still operating limited services, so the replacement bus services between Yeovil Junction and Exeter St Davids will continue to operate.
South West Trains services will not call at Feniton, Whimple and Pinhoe stations today, but the replacement buses will.
South West Trains customer service director Jake Kelly said: "The weather conditions over the past week in the South West have been very challenging and we would like to thank our customers for their patience during this time.
"Despite suffering a setback to our work schedule as a result of heavy flooding on Saturday night, we expect to be able to reopen the line for passengers (on Tuesday), provided the weather does not cause any further setbacks overnight."
The main areas of flood damage on the line occurred between Honiton and Axminster, and on the embankment at Broom Level Crossing near Axminster.
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