Image copyright Getty Images Image caption Commuters have been hit by strikes since April in the bitter row between Southern and the RMT

Members of the train drivers' union Aslef have voted overwhelmingly to strike in a dispute over driver-only operated trains.

The union is accusing Southern railway of wanting to impose changes rather than reach an agreement.

The dispute is separate to a long-running row between Southern and the RMT union over changes to the role of conductors.

Aslef said Southern had "dug its heels in" over the changes.

Southern's drivers who are members of Aslef voted for walkouts by 87%.

The union has announced its drivers will strike on 13-14 December, again on 16 December, and between 9-14 January.

'Two to tango'

Mick Whelan, Aslef's general secretary, said: "Our trade dispute with the company is that there should be no introduction and/or extension of new driver-only operated routes on Southern without the agreement of Aslef.

"We have genuinely sought to reach a compromise with Southern. We have always been prepared to talk to the company and we have always been of the view that it should be possible to do a deal, but it takes two to tango and the company has not been prepared to negotiate," he said.

"They have dug in their heels and forced us to ballot our members."

Image copyright Getty Images Image caption The long-running dispute is over plans for drivers, instead of conductors, to operate train doors

Analysis: Richard Westcott, BBC transport correspondent

This ups the ante in an already vitriolic dispute.

Up until now, Southern had managed to run about 60% of its trains on RMT strike days. Still incredibly annoying for customers but they could normally find a way of getting to work.

Now that just under 1,000 Aslef drivers are joining the fray, albeit on different days, it's hard to see how Southern will be able to run any kind of functioning train service when they walk out.

They're also stopping overtime, which is often vital to running the trains every day.

This dispute has become the defining battle for one of the most contentious issues on our railways, the increasing introduction of what's known as "driver-only-operation" or DOO, where the driver, rather than the guard, takes control of closing the doors.

The unions say it's a safety risk and an excuse to cut jobs in the long run, all to save money. The rail firms and the government argue that it's about modernising the railways, freeing up on-board staff to deal with customers. They also point out that the safety regulator, the ORR, says it's safe and that DOO is already commonplace on many lines.

What happens on Southern is likely to determine what happens on other rail franchises in the future.

'Perfectly safe'

Charles Horton, the chief executive of Southern's parent company Govia Thameslink, said: "Passengers will be rightly furious that these wholly unnecessary and unjustified strikes have been called in the run up to Christmas and in the New Year.

"It's perfectly safe for the driver to have sole responsibility for the operation of a modern train and that's how a third of the trains up and down the country - with the full agreement and support of Aslef - already operate today."

The RMT has been embroiled in a bitter dispute with Southern over changes to the role of conductors.

More stoppages are planned in the coming weeks, in the run-up to Christmas and over the new year.

Southern wants drivers, rather than conductors, to operate carriage doors at certain times.

London Underground drivers are to stage a 24-hour strike on 6 and 7 December, coinciding with a walkout by Southern rail guards.

RMT strike dates: