Last updated: Tuesday 28 July 2026
A temporary timetable will operate on the West of England line from Monday 10 August – click here for more details. In order to make it easier for you to complete your journey with us during this time, ticket acceptance arrangements have been made. Find out more about these arrangements, refunds and vouchers here.
What is Soil Moisture Deficit (SMD)?
Parts of our railway are built on embankments containing clay soil, which normally contains a lot of water.
When we experience high temperatures and dry conditions, typically in the summer, water is removed from the clay soil through heat radiation and nearby vegetation. This causes the clay soil to shrink, which disturbs the ground our tracks are built on.
This is known as Soil Moisture Deficit, or SMD, and it can have a big impact on our train service.
How does it affect the railway?
When railway embankments shift it affects track geometry - the precise positioning, alignment and measurements of our tracks. Sleepers can move out of position, shifting sideways or downwards, which affects the rails on top of them.
Tracks need to be level for trains to run at full speeds, and if the levels, or ‘track geometry’, isn’t right, temporary speeds restrictions are put in place to ensure they run safely.
The West of England Line, an important part of our network, is particularly vulnerable to SMD. The route serves a total of 21 stations over 120 miles and connects London with Exeter St Davids in Devon, Salisbury in Wiltshire and Yeovil Junction in Somerset.
The line between Salisbury and Exeter is a predominantly single-track railway. Speed restrictions along long stretches of single-track can cause cumulative delays and disruption along the whole line, which can have a knock-on impact on other services across the network.
In these instances, temporary timetable amendments can offer better reliability for customers on the West of England line.
Unlike buckled rails or issues with signalling equipment, there is no quick fix for track affected by SMD. It can take weeks or even months of rain for moisture levels to return to normal.
How do we prepare for SMD?
While we cannot prevent SMD, we are better prepared for it, thanks to continuous monitoring of soil moisture levels, enabling earlier identification of risks.
Since we removed the West of England Line’s temporary timetable in November 2025, we’ve worked hard to restore track conditions to a high standard. Over the last year, we have:
We’re closely monitoring soil moisture levels and weather patterns, so that our engineers can understand when track conditions might be affected and react quickly. If we do need to act, this will mean we’ll be able to provide you with more notice about service changes and reduce disruption.
How do we fix the track?
We’re checking track conditions through regular inspections and by using technology such as the New Measurement Train (seen above, passing through Yeovil) which tells us where track geometry needs to be corrected.
To restore track geometry to normal we use tamping machines, which precisely moves ballast back to where it’s needed. However, we can only do that when the clay soil regains moisture, otherwise the tamping will soon be undone by the ground continuing to move.
When the embankments have regained their moisture through rainfall, we’ll tamp the track and remove any speed restrictions. If we experience prolonged spells of dry weather, like we saw in 2022 and 2025, it can take weeks and even months for moisture levels to return to normal.
Longer term improvements
We’re exploring ways to minimise the impact of SMD on both our track and services for customers.
Our engineers have been working with experts at the University of Southampton to understand how better to manage track during SMD conditions, while our train planning teams have looked at a range of options to keep our services as reliable as possible.
Long-term initiatives being explored include:
- Bio-cementation – injecting nutrients into the layer of soil below the track to create a calcium carbon skeleton, which provides more support when the clay soil shrinks
- Injection grouting – injecting expanding polymer foam to fill any voids left by shrinking soil, strengthening the formation of the track
- Self-adjusting sleepers – using sleepers that have a built-in reservoir of chippings, so that when the clay soil below shrinks and leaves voids, the chippings fill the void and prevent the sleepers from moving
- Micro-piling – installing piles in the gap between the rails to provide extra support to the sleepers, which will stiffen the formation of the track and reduce its movement when soil shrinks
Latest information
Following record-breaking temperatures and prolonged low rainfall, clay embankments supporting the railway between Salisbury and Exeter are drying out, affecting the stability of the track.
To keep customers safe, trains will run at reduced speeds between Tisbury in Wiltshire and Honiton in Devon, requiring a temporary timetable.
Following the programme of track and vegetation management mentioned above, and extensive work by our train planning team, we have been able to reduce journey times in this timetable by around 30 minutes compared to last year, with speed restrictions of 50mph instead of 40mph.
From Monday 10 August, train services between London Waterloo and Exeter St Davids will run to a temporary timetable, as follows:
- Services between London Waterloo and Salisbury will continue to run every 30 minutes
- One train per hour will run between London Waterloo and Yeovil Junction
- Every other hour, the London Waterloo service will extend to run to and from Exeter St Davids
- Most journeys from London Waterloo to Yeovil Junction will take three minutes longer than usual, with journeys from Yeovil Junction to London Waterloo taking 13 minutes longer than usual
- Most journeys from London Waterloo to Exeter St Davids will take up to 24 minutes longer than usual, with journeys from Exeter St Davids to London Waterloo taking 27 minutes longer than usual
The temporary timetable limits further disruption and delays while providing a safe and reliable service for customers. The temporary timetable is available for download here.
What is happening?
Spring 2026 was the warmest on record in England and Wales, with well below average rainfall.
In June, the Met Office issued a Red Warning for Extreme Heat for an unprecedented three days in a row. Temperatures of 35C has been recorded in three consecutive months (May, June and July) for the first time, and large parts of England have so far recorded 0% of the expected rainfall in July.
Soil moisture levels in the south west have decreased significantly, at a faster rate than last year, when we were forced to implement a temporary timetable between August and November.
The graph below illustrates the amount of moisture necessary to return the soil to its maximum saturation.
What happens next?
For ground conditions to improve, which will allow us to correct track geometry, we will need to see more rainfall and lower temperatures.
We will continue to closely monitor ground and track conditions and provide updates as they become available.
Please check back for updates.
