The strike will end at 1859 BST Thursday but a normal service is not expected to resume until Friday morning.
There were hopes of the deadlock between LU and the RMT being broken with both sides agreeing to engage in fresh talks on the Acas proposal.
An Acas spokesman said the conciliation service had sent a proposed solution on redundancies to the RMT on Wednesday night which the union had amended and returned to Acas. The proposal was sent to TfL on Thursday.
A TfL spokesman said: "We are preparing for further discussions at Acas as soon as possible."
General Secretary of the RMT Bob Crow said: "I hope that they are serious about their pledge this morning to talk as soon as possible.
"RMT are geared up and ready to go."
Commuters struggled to get in to work as buses continued to be overcrowded and roads were gridlocked.
London Mayor Boris Johnson met commuters making their way in to work near London Bridge station.
He said: "I think the people of London have shown fantastic resilience and indomitability in getting to work in such overwhelming numbers."
Docklands Light Railway, London Overground and trams are expected to run as normal and the TfL has drafted in an additional 100 buses while offering escorts for cyclists and a free river ferry service.
On Wednesday LU said 120 trains were in service but the RMT accused LU of overstating the numbers.
Mr Crow also criticised drivers' union Aslef for hitting out at the RMT in calling on its members to support the strike.
Some people endured journeys delayed by hours
"One thing that I would never do as a trade union is criticise another union for going on strike," he said.
Former London Mayor Ken Livingstone said Mr Johnson has made a "fatal mistake" by not engaging in direct talks with the RMT which members perceived as an "anti-union agenda".
He said: "They need to both be in the room and Boris has made this fatal mistake of saying that 'I'm not going to meet while there is this threat of a strike or a strike going on'."
But the strike did not deter almost 58,000 fans from attending England's World Cup qualifier match against Andorra at Wembley Stadium.
Mainline train services did not stop at Wembley Stadium Station for safety reasons, leaving fans to walk from nearby stations to the stadium.
The London Chamber of Commerce has estimated the capital's economy will lose more than £100m over the course of the strike.
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