(ShareCast News) - Long-suffering commuters on Southern Railway services were handed some reprieve on Wednesday, with the news a planned six-day drivers strike was to be halved.Drivers belonging to the Aslef union were due to walk out for six days from 10 January, wreaking havoc in the first full working week of the year.The action will now only last for three days, with normal service resuming from 14 January.It wasn't enough for London mayor Sadiq Khan, however, as he called for the remaining three day strike to be called off and for Aslef and Southern to return to the negotiating table.But the union's general secretary, Mick Whelan, said it was not rolling back on the dispute, and he warned of further strikes.The dispute stemmed from Southern's plan to change the role of guards on some of its long distance services, giving door responsibilities to drivers.Unions have said that would be a slippery slope towards the removal of guards altogether, although Southern pointed out that its metro operations in London have been driver-only operated for a number of years.Southern is a part of Govia Thameslink Railway - a joint venture between FTSE 250 firm Go-Ahead and French company Keolis - which also includes the Thameslink, Great Northern and Gatwick Express operations.