The rush hour will start early in London tonight as workers try to get home before the start of a strike at London Underground, which will bring the system to a halt.
Members of four unions will walk out from 6.30pm, crippling the Tube network until Friday morning.
Workers are in dispute over pay and conditions for a new all-night service planned to start next month at weekends on some lines.
Transport for London (TfL) said extra bus and river services will be laid on during the strike, but warned that all public transport and roads will be busier than usual.
People were advised to complete their journeys by 6.30pm tonight and to travel earlier if they can.
Workers and tourists will face a day of disruption tomorrow as the system is completely closed for the second time in a month.
Unions have called for a delay to the planned September 12 start of the night Tube so that further negotiations can be held to try to break the deadlocked row.
RMT leader Mick Cash said: "Despite all the bluster from mayor Boris Johnson, Londoners need to be aware that night Tube was rushed and botched from the off, and that is why five weeks before it starts staff are striking because they will not accept that their work/life balance should be wrecked to plug the gaping holes in staffing capacity that should have been dealt with from day one.
"It is a measure of the current shambles that no further talks are planned and staffing posts essential to delivering a safe extension of operating hours are still being axed."
A spokesperson for the mayor said: "Despite the fair, sensible and generous offer on the table - which will see no-one working more hours than they do today - the unions have chosen not to put it to their members and to reject it outright.
"The fact is that the night Tube is well supported by Londoners and by businesses across the capital. The Mayor believes that most reasonable people see its introduction as a progressive move for transport in our city."
LU said it has drawn up rosters for the September 12 start.
Chief operating officer Steve Griffiths said: "The draft rosters clearly show how we propose to incorporate night Tube duties whilst protecting the work-life balance of our staff and offering them choice.
"Our guarantee is that in the transition period our staff will have at least the same number of weekends off as today. After that, drivers will have the choice as to whether or not they continue to work the night Tube shifts.
"Alongside that, no one will work any more hours than they do now, everyone will still get two days off in seven and staff will still be able to swap shifts to get the work-life balance they want.
"These commitments, alongside the very fair pay offer that we have put forward, represent a very good deal for our staff.
"If the unions continue to believe that there are issues with work-life balance, then the only way to settle them is by keeping talking. We remain available for talks at any time."
TUC assistant general secretary Paul Nowak said: "The Tube network is vital to the travelling public and the economy, but London Underground must not ride roughshod over the wellbeing of their employees.
"Any significant change to working hours should be the subject of proper negotiation and agreement. Anyone who was told by their boss that they would have to start working through the night would expect that to be agreed and not imposed.
"The TUC always encourages employers to positively engage with unions on fair and sensible arrangements for night working, so that we continue to enjoy the social benefits night workers give us without harm to them or the public."
The strike will hit fans travelling to Stamford Bridge for Chelsea's friendly game with Fiorentina.
LU said it is still appealing to unions to call off the strike.
In a message to commuters managing director Nick Brown said: "I am sorry that your journeys this evening and tomorrow will again be disrupted by the unions.
"We listened to their concerns over work-life balance and put forward an extremely fair revised offer."
He added: " We continue to urge them to call off the strike, put the new offer to their members and not subject Londoners to further unnecessary disruption. We remain available for talks at any time."