Image copyright @TeddyPB Commuters are braced for rail chaos across London and the South East amid strikes on the Southern network after last-ditch talks broke down.
The RMT union is staging a five-day walkout in a row over the role of conductors.
Southern has promised to run 60% of its normal timetable.
Parent rail firm Govia Thameslink (GTR) is in a bitter dispute with the RMT union over plans for drivers to operate the doors on new trains using CCTV.
Members have already staged several one-day strikes over the plans, but the union fears job losses and has safety concerns.
The RMT said the safety of the travelling public on "dangerously overcrowded trains and platforms" was "the fundamental issue at the heart of this dispute".
Lines with no rail service during the strike are expected to include:
- Havant - Chichester
- Horsham - Dorking
- Redhill - Tonbridge
- Haywards Heath - Seaford
- Oxted - Uckfield
- Eastbourne - Ashford International
See Southern rail's map of revised services during the strike
Last month, Southern brought in a reduced timetable in response to continued cancellations and delays, blaming issues with crew availability during a dispute with the RMT.
The revised schedule saw 15% of Southern trains cancelled. It previously ran 2,242 services every weekday.
GTR has faced repeated calls by unions, MPs and commuters for it to be stripped of its franchise during the disruption.
Two other rail unions, Aslef and the Transport Salaried Staffs Association, are balloting their members about strike action in separate rows about new rosters and planned ticket office closures.
Commuters have staged protests in London and the South East over continued disruption on the Southern rail network.
Passengers have described 70-minute commutes taking three or four hours, being "turfed off trains" and feeling "utterly powerless" in the ongoing saga.
Shelley Atlas, Brighton line commuters chairwoman, said: "We are obviously very concerned at the length of time this has gone on.
"Many of our members are very angry at having to face a further strike, and one lasting five days.
"Whilst some rail passengers may be able to work from home there are many who are not able to. Members are concerned as to when this will end."
Southern is the main operator for Sussex and east Surrey and also runs services in London, Kent, Hampshire and Buckinghamshire.