As athletes poured into London for the 2012 Summer Olympic Games on Monday, many were treated to an unintentional tour of the city as bumper-to-bumper traffic, stopped trains and crowded airports created travel chaos.

In what's being described as Britain's biggest peacetime transport challenge, Heathrow expects 236,955 people to fly in or out on Monday, including athletes from 50 nations across the globe. That figure is about 25 percent above Heathrow's typical numbers and would break the previous record of 233,562 people set on July 31, 2011.

July 24 is expected to be the busiest day for arriving athletes with 1,262 competitors, along with thousands of others, due to arrive that day. August 13 is expected to be the busiest day for total departures with some 137,000 people -- or the equivalent of 1.7 London Olympic Stadiums full to capacity -- expected to leave London via Heathrow Airport.

Heathrow is but one of six international airports serving London, but it's the only airport where participants can get their Olympic credentials and, consequently, will receive an estimated 80 percent of Olympic visitors, athletes, officials and members of the media. Some 12,850 Olympic athletes and 7,000 Paralympians are expected to travel through the airport in the coming weeks.

Heathrow operator BAA enlisted 1,000 volunteers to greet Olympic arrivals and created special teams to handle oversize items such as Olympic javelins and racing bikes. Hundreds of immigration agents, including several retired border officials and police officers, were also at the airport to ease the long lines that have plagued Heathrow in the months leading up to the Games.

An official Games Lane was opened Monday along the vital M-4 highway linking Heathrow and central London to help ease transport for Olympic officials, athletes and VIPs. That didn't, however, stop traffic from building up. A 32-mile-long traffic jam caused, in part, by an accident on the M-4 made travel anything but pleasant Monday.

Travel experts had warned that an accident on the roads in London during the Olympics could lead to a perfect storm, because the Games Lanes have reduced the amount of space for ordinary traffic.

What they didn't predict, however, was that bus drivers would be ill-informed about how to get to Olympic venues.

U.S. hurdler Kerron Clement, a defending Olympic silver medalist, took to Twitter Monday morning after his bus struggled to get to the Olympic Village in Stratford.

Um, so we've been lost on the road for 4hrs. Not a good first impression London [sic], he tweeted. Athletes are sleepy, hungry and need to pee. Could we get to the Olympic Village please?

A group of Australian athletes also reportedly found themselves lost on a bus for around three hours. Under normal conditions, the drive should take about an hour.

Hugh Robertson, the sports and Olympics minister, apologized to athletes who had a rough go of it getting through London.

If people have been on buses that have got lost, then it is, of course, regrettable, he told the Daily Telegraph. I am extremely sorry, and clearly the drivers need to know where they are going.

The London Organizing Committee of the Olympic and Paralympic games argued that the vast majority of bus journeys went off smoothly but conceded there may have been one or two journeys taking longer than expected.

If they took four hours, then they will have seen far more of the city than they might otherwise have done, quipped London Mayor Boris Johnson, making light of the situation.

There are around 30 miles of dedicated Games Lanes, with the majority in central London and east toward Olympic Park at Stratford. Additional lanes will open up on July 25 just ahead of the games, which begin July 27.