Work to prepare the railway in Bath for electrification has begun.
The £50 million project includes lowering the track to allow for overhead power lines for new electric trains.
It will take six weeks and mean some delays. Network Rail has been careful to ensure the city's architecture is protected.
Completing the electrification of the Great Western line between London and the West is a top priority, the Transport Secretary has announced.
It means that two other major schemes - in the Midlands and across the Pennines - will be delayed.
Patrick McLoughlin told MPs that delays and problems, which have seen the costs treble to £1.7bn, "could and should" have been foreseen by Network Rail, whose chairman is being replaced.
Later, he told Bristol East MP Kerry McCarthy there were "big engineering challenges" but new trains should be operating on the electrified line in 2017 or 2018 (a year later than originally planned).
Some trains between Bristol Temple Meads and Bath Spa may be cancelled due to a person being hit by a train.
Currently all lines are blocked and train operator First Great Western says customers should check before they travel.
Commuters say they're furious they're paying hundreds of pounds a month for train journeys where they can't even get a seat.
While money's being invested in mainline services across the South West, there are claims that smaller stations and branch lines are being overlooked, meaning hundreds of passengers are commuting to Bristol in cramped carriages. Laura Makin-Isherwood reports.
First Great Western are warning of continuing disruption on the trains because of the recent storms.
Services between Bristol and London are running as normal, but services west of Bristol are subject to lengthy delays and cancellations.
Passengers are being urged to check before travelling.
There's major disruption on the trains this morning between Bridgwater and Taunton, and Taunton and Plymouth/Penzance.
Meanwhile, trains from the West Country into London are also subject to delays.
First Great Western said it would only be able to run four trains an hour between Reading and London Paddington because of flooding near Maidenhead.
South West Trains is operating a heavily-curtailed service.
Trains are again running through Crewkerne and on into Devon following yesterday's landslip - but at speeds down to 5mph. A short while ago South West Trains said services were resuming between Waterloo and Exeter St Davids.
Yesterday Network Rail said initial assessments showed it could be some time before the was re-opened.
A landslip near Crewkerne has halted rail services through Yeovil Junction, effectively severing the link through to Devon and Cornwall. Network Rail says the route from Bridgwater is blocked by the flooded River Parrett, while the main line from Castle Cary is blocked by flooding at Athelney.
It is likely that the slip at Crewkerne will be closed for a least a week, but it is too early to say when the line through Bridgwater will reopen. The floods are currently being blown into waves by the high winds in the area, which are washing away the stones the track rests on.
The landslip and other weather-related problems are affecting services as far away as Bristol Parkway, where bus services have been laid on between there and Exeter St Davids.
Trains are suspended on Arriva Trains Wales between Lydney and Gloucester due to flooding.Replacement buses are being arranged.
The third and last transformer is on the last leg of its journey from Didcot Power Station to Avonmouth docks. It is almost 100m long and 5m wide and will take up two lanes of motorways and the entire width of normal roads. It is travelling at an average speed of 4 mph, slower on hills.
- The load stayed at Tog Hill parking area near Bath overnight
- This morning it is undergoing safety checks before leaving 8-9 am
- It will travel to Wick by the A420 (11am) where steel plates will be laid so it can pass over two culverts.
- It will continue to the A4174. At Bromley Heath roundabout the road will be closed to the M32 junction so the load can travel on the wrong side of the dual carriageway to avoid a weak bridge.
- At the junction with Bristol Road, the load will return to the correct carriageway and continue onto the M32
- It will then rejoin the M4 before taking the M5 to Avonmouth.