Well the argument would be that if we didn't have to pay guards we could have more drivers for the same amount of money.
The whole "wrong side release" problem that is apparently caused by not having a guard could be mitigated using the new technologies becoming available.
For instance a Eurobalise could be positioned at the start of a platform (or logical part platform in case of places like Doncaster) reporting the length to the start of the platform and the length to the end of the platform, as well as what side it is.
You could then programme the train to use its onboard odometers to determine whether or not the doors of the train are actually platformed on a valid platform - if not the system will ask the driver to confirm that he does in fact want to release the doors.
(Preventing the system preventing the doors from opening in an emergency).
Although most balises could be inexpensive passive ones some would have to be linked to the signalling system so that trains in Doncaster style platforms do not release doors on the crossover in case of an overshoot.
This would also prevent doors opening on stop shorts.
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+1.
The guard is in theory the last line of defence able to arrange protection of the line and give accurate information for the most expeditious emergency services attendance in the case of a serious incident rendering a driver 'unavailable'.
But in the days when it will soon be possible to track every train throughout the entire system using things like GSM-R and maintain contact with the driver or other train crew at all times, does the Guard really have any significant role to play in 'protecting the line'?
If contact is lost with a train (in a way not indicative of a shut-down) and the driver cannot be contacted any close train on the opposite line could be asked to approach 'able to stop short of obstructions' to guard against an accident blocking lines.
They could also contact someone from the emergency services to go and look (if they are closer than railway personnel) as the control centre will know the last 'good' location of the train to the inch.
Computers give us eyes in every cab, assuming video could be streamed (in relatively low resolution to save bandwidth) from cabs to the control centre and buffered the 'last moments' of a 'lost train' could be played back to gain clues as to what has happened.