Commuters are warned to avoid South West Trains (SWT) on Friday and Monday as a drivers' strike threatens to cripple services in southern England.
The strikes are expected to cause serious disruption
On many routes there will be no trains and only one in five is likely to run overall if the row is not resolved.
Emergency timetables were handed out earlier to commuters who are urged to avoid rush hour travel if possible.
Tens of thousands of people take SWT services into London's Waterloo station during weekday rush hours.
Talks on Tuesday failed to resolve the row over managers being used to drive trains during a previous strike.
Services that run during the walkouts on Friday and Monday will begin and end earlier than usual.
"We therefore advise you to avoid the peak hours and to make alternative travel arrangements on these days if you possibly can," said SWT operations director James Burt.
SWT usually runs 1,700 trains every weekday between Waterloo and the south west and south east, including Bristol, Plymouth, Reading, Weymouth and Brighton.
'Strike breaking' row
The dispute began as a row over taxis being provided for drivers facing late-night or early-morning shifts but escalated after SWT used managers to operate trains during walkouts.
Drivers' union Aslef claimed safety was compromised, a charge strongly denied by the company.
An SWT spokesman said: "What the union sees as strike breaking, we see as customer service."
An Aslef spokesman said the union had put forward proposals that could resolve the dispute.
But an official said it was a "pretty sure bet" that the strikes will go ahead as planned.