We own, operate and develop the rail infrastructure connecting the South of England to London Waterloo. We tweet Mon-Fri, 9am-5pm. 24/7 helpline: 03457 11 41 41
As it’s an insulated joint, it’s part of the signalling system too, and will require testing before we run trains.
We are unable to run trains over the crack in the picture as its location means it could cause a derailment if the rail was to come apart under a train. 
The very hot and dry conditions of recent weeks has dried out the clay soil beneath the embankments between Tisbury and Gillingham 🌡️
@SW_Help Our signallers can see where trains are using technology called "axle counters" which are usually very reliable. They literally count the axles of trains passing each signal and make sure each train is complete and the track is clear by comparing the numbers. /2
@LondonWaterloo @SW_Help The scale of the problem is such that we cannot control signals in the red box, from New Malden to Esher, so trains are having to get permission to pass all of them at red. They do this by phoning the signaller at New Malden, and again when they leave the section at Esher. /2 
The train detection equipment that controls access to the Loop, where trains pass each other , has been failing intermittently and can’t be relied on - effectively meaning signals turn from green to red and back again. /2
@SW_Help @GWRHelp We have just endured one of the wettest autumns since records began more than 100 years ago. This, combined with a month’s worth of rainfall over the past five days, has put unprecedented strain on our railway network to do something it wasn’t designed to do. 2/11