LONDON -- London's extensive subway and train system is facing a major test with officials expecting up to 3 million more journeys a day during the Olympics.
Athletes, officials, fans and millions of working Londoners - including Prime Minister David Cameron - will bustle and battle to get about.
"It will get busy," the city's transport chief, Peter Hendy, said Tuesday. "It has got busy already. There will be some queues."
On Monday night, two train links serving the Olympic Park - one subway line for central London and another for an overland train - temporarily went down as thousands of volunteers rehearsed for Friday's opening ceremony.
"We got everybody home. It was a successful dress rehearsal and we're looking forward to delivering the real thing on Friday," Britain's Transport Secretary, Justine Greening, said Tuesday. "But, of course ... on a transport system as complex as London's, things do go wrong."
Parts of the London underground system trace back to the 1860s. The system averaged about 12 million rides a day before the Olympics, and is expected to rise up to 15 million journeys a day.
"Even though one line is down, the rest were working. That shows part of the resilience that we've got," Greening said.
Cameron said he's going to use public transport for some trips during the games and not the VIP Olympic road traffic lanes that open Wednesday.
Britain spent over 6.5 billion pounds ($10 billion) since winning the bid on upgrading London's sprawling transit system.
The new high-speed "Javelin" train carries people from a central London transport hub out to the Olympic Park in the eastern part of the city in about six minutes. Other subway links in east London have been greatly modernized.
But public transport will have challenges all over with venues spread across London.
Tennis will be at Wimbledon in the leafy suburbs of the southwest, while beach volleyball takes place in the heart of the city, close to Cameron's Downing Street residence.
Along with too many people, the weather can also be a problem for the transit system - and it even may be too warm, at times. Another train station in east London was out of service for a while Monday because of high temperatures that affected overhead power lines.
"It's part of the challenge," Greening said.
While trying to provide a seamless transport service for the 18,000 athletes, 11,000 officials, 26,000 accredited media members and millions of tourists at the games, London also has to remember its own busy citizens.
Officials hope the Olympics "don't disrupt Londoners more than we have to," Hendy said, but some locals may feel like second-class citizens over the next two weeks.
Dedicated Olympic traffic lanes, which come into operation at 6 a.m. on Wednesday, already have left some Londoners unhappy. Drivers of the famous black cabs demonstrated Monday over the fact that they can't use the special Olympic lanes.
Traffic could be gridlocked at times. On Tuesday, a bus carrying reporters crashed into a car near the main hotel area for the media, causing delays.
But it's not all bad news.
Some people said their journey home from the opening ceremony rehearsal at the Olympic Stadium was great, even with the two links going down. And travel is free for ticket-holders to their events.
Also, wireless Internet is now available inside some London subway stations for the first time. If you're stuck in those spots, at least you could keep track of the travel chaos online.