Why is TERN useful?

 It does not require any fixed infrastructure.

It does not require a secure communications link as the security for token transmission is contained within each of the units.

It requires the very minimum of physical input from a train driver.

It gives a visible confirmation of movement authority to a driver.

 It has a system architecture that recognises that it is based on SOUP    (Software Of Unknown Provenance) and so uses various stratagems to mitigate  against any software anomalies.

 The control unit is always in control – sequences cannot get out of phase.

 The system cannot be paralysed by a failed slave unit.