TVM (Transmission Voie-Machine or track-to-train transmission) is a form of in-cab signalling originally deployed in France and used on high-speed railway lines. At high speeds it is not possible for a driver to accurately see colour-light based railway signals along the track-side. Currently the London to Faversham route with the Class 395 has TVM signalling.

Class 395 Stratford International L2F

The Class 395 uses TVM on HS1, the high-speed line out of London St Pancras International. The driver uses conventional colour light signalling on the classic network.

Signalling information is instead transmitted to the train and displayed as part of the train controls. The driver is shown the safe operating speed, displayed in kilometres per hour. The TVM-430 system transmits more information than traditional signalling would allow, including gradient profiles and information about the state of signalling blocks further ahead. This high degree of automation does not remove the train from driver control, although there are safeguards that can safely bring the train to a stop in the event of driver error.

How to read TVM signallingEdit

In the cab the driver will find a double row of square indicators. This is where target speeds for the current and subsequent blocks are displayed to the driver, in the form of numbers (in km/h) on a colour-coded background. Full line speed is indicated in white numerals on a green background, while slower aspects are indicated in white numerals on a black background and a full stop is indicated as "000" on a red background.

TVM example

TVM Display showing position of numbers and example numbers. Colours are a representation but font colours are correct.

Line Speed SectionEdit

This section displays white numbers on a green background and can be either static or flashing. This section only displays the numbers 225, 200 and 160. It shows that the train may proceed to the maximum speed of the line displayed.

Warning SectionEdit

This section displays black numbers on a white diamond in a black background and will either be static or flashing. This section warns the driver what the speed is at the next signal. By example: if it is flashing 160 then the driver should aim to be doing less than 160 by the next signal. If it is a static 160 then that means at the next signal the speed limit will be 160.

Execute SectionEdit

This section displays a black background with white numbers and will be either static or flashing, telling the driver this is what they should currently be doing. A static execute function would normally appear after a static warning indication. The 000 and three solid red squares only appear in this section.

TVM by ExampleEdit

Changes in speed limit can occur anytime regardless of where the driver is in a block. Speed limits can only go down at a signal.

For the sake of example,say the TVM is displaying a static 225 line speed until the driver passes the next signal, when it displays a flashing 225 line speed. This means that the speed past the next signal is going to display a speed less than this, so the player needs to be slowing down and be doing less than 225 by the next signal.

When the driver reaches the next signal the display shows a flashing 200 warning indication. This indicates the driver needs to continue braking to below 200 as the next signal is going to display a lower speed. At the next signal however, the driver gets a static 160 warning indication. This means that the driver needs to be doing 160 by the next signal but doesn't necessarily have to continue decreasing speed as the next signal will display a static 160 execute indication. So the driver can now do a maximum of 160 until the display tells the driver otherwise.

When speeds are going down there is limit on how far they can go down from certain speeds. If the driver has a 225 displaying then it will not drop straight to 000. It would have to count down through 225, 170, 000. The TVM can only drop to 000 from a maximum of 170. And 225 can only drop to a minimum speed of 170 so it will not go from 225 to 160. Below the TVM display is the speedometer, where the continuously varying target speed is indicated, as well as the current speed. (Speed is measured by a redundant tachometer to a precision of 2%.) For an indication, under a 300 km/h aspect, the computer will take action only if the train exceeds 315 km/h.

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