The train drivers’ union Aslef has cut the number of strike days next week from six to three.
But it has also announced three fresh strike days in late January in its dispute with Southern and its parent company Govia Thameslink Railway (GTR).
Aslef members were due to go on strike for six days – from Monday 9 January to Saturday 14 January.
Instead, train drivers will refuse to work on Tuesday 10 January, Wednesday 11 January and Friday 13 January.
Given a possible 24-hour Tube strike from 6pm on Sunday (8 January), the union expects to achieve a similar result from half the number of strike days.
Disruption on non-strike days will be exacerbated by the current overtime ban as Southern does not employ enough drivers to cover every service and relies on drivers working voluntary overtime.
Aslef members will also strike on Tuesday 24 January, Wednesday 25 January and Friday 27 January.
Southern bosses are trying to lay on replacement buses for some parts of network next week, although not Brighton and Hove. And National Express has said that it will run more coaches between Brighton and London.
Aslef said today: “Aslef represents nearly all the train drivers in the UK, across every company. Our members are professionals who safely and securely transport millions of members of the British public from A to B each day.
“Driving a train carrying more than 1,000 people is a demanding and responsible role which our members take extremely seriously. The job of a train driver is to drive the train – and that requires total concentration.
“Going on strike is an action of last resort for any worker. The reason for strike action on Southern Rail is because of a dispute with the company.
“Southern is withdrawing safety trained guards from its trains without consulting its staff or negotiating with their trade union reps.
“The driver of a 12-car trains carrying 1,100 passengers in the rush hour will have just two seconds to check 24 sets of doors.
“Professional train drivers know that this risks passengers’ safety. They may not see someone falling between the train and the platform, nor someone caught in the doors. And in an emergency, passengers may be at risk if the driver is working alone on the train.
“And worse, they haven’t properly consulted but have tried to impose changes through bullying and intimidation.
“No wonder there’s been such a huge loss of trust and goodwill on the part of union members towards the company. And it is this that has left us no option but to go on strike.
“Aslef’s constructive relationships with other rail companies show there is a better way. Earlier this year, we negotiated a positive agreement with ScotRail in Scotland. Southern have not been willing to follow this example and negotiate an agreement with us.
“The dispute between Aslef and Southern has also been made worse by political interference. It was clear that the Southern franchise was failing even before this dispute – it doesn’t even employ enough drivers to run all its scheduled services.
“Nonetheless, Transport Secretary Chris Grayling has lined up behind the discredited company as it has made a mockery of its passengers and staff.
“With record passenger numbers travelling on the trains, we need more rail staff, not fewer.
“We will get better services for passengers by investing in modern railway infrastructure and rolling stock – not by downgrading guards, taking them off trains and leaving drivers to manage trains on their own, something they are not prepared to do, given the risk to passengers.
“We understand the anger felt by of regular commuters on the Southern franchise area and we share their frustration.”
Southern said: “This is a cynical ploy to minimise the impact on Aslef’s drivers’ pay packets and maximises misery, disruption and hardship for passengers.
“Aslef’s move shows pure contempt for the travelling public and it still causes massive disruption over next week.
“These strikes are pointless and they should call the whole thing off and let common sense prevail.”
Southern said that none of its train services would run on the three strike days next week.
But it said that it was “putting in place a number of alternative measures to try to help those commuters who have essential travel needs”.
Other train operators, such as Thameslink, which should be running as normal, will accept Southern tickets.
The company also said that it was “advising people to work from home or remotely if they can, stagger journeys if possible and to only travel if it is essential and allow plenty of extra time for journeys”.
It added: “Details of car share schemes are being made available to passengers on Southern’s website.”
And it said: “To ensure public safety, crowd control measures will be in operation at all its stations where trains or buses will operate.”
Southern’s passenger service director Angie Doll said: “There will be significant disruption and hardship next week caused by these pointless and unnecessary strikes.
“With this package of measures, we are putting in place a very limited number of alternative options to help people with essential travel needs get where they need to be.
“Unfortunately, there is no practical way we could replace 2,000-plus trains we run each day with buses but what we are doing is providing transport to link some passengers into other operators’ stations where services are running normally.
“These buses will run from a small number of stations and space will be very limited so we are asking those who don’t need to travel, or who have a viable alternative, to leave the space for those who have no other option.
“Anyone who does travel should expect to queue, plan for longer journeys and realise the service they join will be exceptionally busy.
“We are massively grateful to all the operators who are helping us in our efforts to keep passengers moving.
“This strike is futile. Drivers are now operating the doors on over 75 per cent of our trains and our onboard supervisors have moved into their new roles.
“It is now time the union move on too, and join us in delivering a modern railway for everyone.”