Colin King, a retired competence manager for Southern Railway, believes driver-only operation (DOO) trains are not safe.
The issue of DOO trains is at the centre of months of strike action by conductors, who would no longer close train doors on Southern trains under the changes but be more involved in providing customer information.
Earlier this week Southern announced it was cutting 341 trains a day to run a revised timetable in response to the strikes and staff sickness.
Mr King, 70, who lives in Anchorage Park, Portsmouth, worked for the company for 17 years and has concerns.
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He said: ‘In 2001 I was part of the team that brought in the rolling stock and trained most of the conductors to operate these units.
‘I considered then and still hold the opinion that they are not safe to operate in driver-only mode.
‘The driver does have external cameras on each vehicle, however, once he/she takes power they go blank and he is therefore unable to see what is happening on the platform.’
And he added: ‘I myself had an incident while working a 12-coach train.
‘Having completed station duties I closed the doors, then looked back along the train to confirm all was clear, to my consternation I observed the majority of a walking stick protruding from a door on the last coach.
‘The elderly gentleman had taken longer to get to the door and as it closed tried to get the safety system to withdraw the doors.
‘The thickness of the walking was insufficient and the doors closed and locked. I was able to get the driver to release the doors.
‘Had this train been DOO the driver would not have detected any problem and start the train resulting in the potential for people walking down the platform to be injured or worse.’
Mr King also believes conductors to open doors would still be needed from Warblington and further into Hampshire as this is on the South West rail network, which has conductors controlling doors.
Officials at Southern have stressed that 40 per cent of their trains are already driver-only and have operated safely for 25 years.
Earlier this year the independent Rail Safety & Standards Board said that DOO trains offered ‘no increased risk’ compared to train operation with a conductor closing the doors.
The RSSB added that the trains could ‘potentially deliver some safety benefits’, due to the removal of the risk of miscommunication between driver and guard.
At the time, Southern Railway called on the unions to ‘cease their alarmist scaremongering about safety’.