A strike by train drivers on Southern Railway has crippled thousands of services and is causing misery for hundreds of thousands of passengers.
Aslef members mounted picket lines outside stations at the start of a 48-hour walkout in a dispute over driver-only trains, with another strike planned for Friday.
Normally busy railway stations were deserted as passengers worked from home, took the day off or attempted to drive.
Here is everything you need to know about the strike.
- How long will the disruption last?
Members of Aslef are on strike on Tuesday, Wednesday and Friday this week and again from January 9 to 14.
- What is the dispute over?
Aslef is opposed to driver-only trains, citing safety concerns as passenger numbers grow, and warning that in-cab monitors, allowing them to check when it is safe to close doors, do not always work.
- Why is Southern in favour?
Southern say it is perfectly safe for the driver to have sole responsibility for the operation of a modern train, which is how a third of trains up and down the country operate, with the full agreement of Aslef.
- How many passengers, and services, will be affected?
Around 300,000 passengers use Southern's 2,242 services on a weekday.
- When was the last time so many train services were cancelled?
It will be the worst disruption since a lengthy dispute in the mid 1990s involving signal workers.
- Is this the only dispute affecting Southern?
No - the company has been embroiled in a long-running row with the Rail, Maritime and Transport union over changes to the role of guards, which has sparked a series of walkouts over the past few months.
- When is the next RMT strike?
RMT guards will strike next Monday and Tuesday, and again for three days from New Year's Eve.
- Are services being disrupted on non-strike days?
Southern's passengers have suffered delays, cancellations and last-minute alterations for months, even when workers are not taking industrial action, with other issues including a shortage of staff, high sickness levels, signal failures and train faults.
- Have passengers been offered any compensation?
The government has announced that annual season ticket holders will receive a payment equivalent to one month's travel, with quarterly, monthly and weekly season ticket holders being able to claim an equivalent payment for the ticket type.
- Are Southern's fares being frozen because of the disruption?
No. Fares on Southern and Gatwick Express - both owned by Govia Thameslink Railway (GTR) - will rise by an average of 1.8% from January 2, in line with other train operators' annual increases.
- How much has the dispute cost Southern?
GTR has estimated that the likely combined cost of industrial action, revised timetable and poor performance will be around £38 million for this financial year
- What has the government said about the strike?
Transport Secretary Chris Grayling said he is "mad" about the strike, but insisted he can't "order" Southern rail workers back to work, and that if he had "the power" to do so he "would do it".
He said: "We've been trying to get the unions around the table for the last few days to sort out a deal that will end this, (but) they just don't seem to want to come.
"This way of working is already happening on this network, it's not about introducing something new. It's already happening.
"The reason that this strike has arisen is because we are investing as a nation £2 billion in new trains so we can phase out the older trains.
"The new trains use a technology that controls the doors from the driver's cab. Already about half the trains on the network are operating like this. The unions have been fighting against something they're already doing."