LONDON, England (AP) — London's overstretched transit system creaked and groaned but appeared to be coping with the strain on the first working day of the Olympics.

Monday morning's rush hour was the biggest test yet of the host city's transport network, as spectators and tourists heading for the games joined the city's workers during rush hour. The games opened Friday night.

Prime Minister David Cameron said the system was coping well.

He said there were "lots of challenges, we've got to overcome them one by one. I think everything at the moment is looking good."

Drivers faced the most difficulties. An accident closed a section of the M4, the highway that links Heathrow Airport to London. The route, busy at the best of times, has been narrowed as it approaches the city with the creation of "Games Lanes" reserved for official Olympic traffic.

The lanes — nicknamed "Zil lanes," after the limousines used by Soviet apparatchiks — caused worse-than-normal backups on main roads near games venues, especially around Olympic Park in the east of the city.

London Mayor Boris Johnson said organisers had turned off some of the lanes because more Olympic officials than expected were using public transport. He said even International Olympic Committee President Jacques Rogge had used Docklands Light Rail trains to get to Olympic Park.

"It turns out a lot of the Olympic bureaucrat types who could go in the Games lanes ... are using public transport," Johnson said.

Sporting events are taking place across London, from the Olympic Park in the east to tennis at Wimbledon in the southwest, equestrian contests at Greenwich in the southeast and soccer at Wembley Stadium in the west.

Trains and subways were running without the delays that often plague London commuters. Some were less busy than usual, with travelers seemingly heeding warnings — broadcast repeatedly on station loudspeakers for weeks — to plan ahead and take different routes if necessary.

Transport for London, which runs the capital's public transport network, warned commuters to avoid some subway lines and interchange stations, and urged them to leave extra time for their journeys.

London's subway, the Tube, saw some delays and suspensions last week, while road traffic was also disrupted by Olympic lanes reserved for athletes and officials. Monday evening's rush hour was expected to be an even bigger test, with one of the city's main commuter rail stations, London Bridge, due to be partly closed to prevent overcrowding.