And it is not just the roads. Two-hour immigration lines at London's Heathrow Airport made travelers angry a few months ago. That is bad for tourism and business. Officials say they have addressed the problem, and there is a special terminal just for people participating in the Games.

Train stations will also be busy, particularly St. Pancras International, where trains run to and from the European continent.

The often-crowded Underground train system, The Tube, is planning for a 25 percent increase in passengers during the Olympics. The nearly 150-year-old system is prone to breakdowns, so extra repair crews will be on standby, and extra station staff will be on hand to give directions.

And London just opened a new transport line - a cable car that goes between two Olympics venues and will remain as a tourist attraction.

In addition to the millions of journeys by Olympics visitors, all the transport lines will have to handle their regular traffic of commuters and visitors. That's why the Games will be held in late July and early August, a time that many Londoners are away on vacation.

Still, transport will be crowded and confusing. So it will probably be a good idea to stay close to someone if you can.