More than half a million of Sydney's four million residents plan to flee the crowds and traffic gridlock expected in the city during the Olympic Games in September, a new survey showed yesterday.

The survey, conducted this month by the airline Ansett Australia, found 14 per cent of Sydney's population would be leaving during the September 15th to October 1st event.

Few Sydney residents have any faith that rail or rail networks will be able to cope with the heavy demands. A rail supremo, appointed last month to try to fix a system plagued by breakdowns and accidents, admitted two weeks later that it could not be done in time. The pressures during the period of the games would be "extreme", he said.

Even at the best of times, all major roads through Sydney are heavily congested during ever-widening peak periods and a single accident or breakdown can very quickly ripple throughout the city.

The survey also found the rich most likely to want to go elsewhere, amid widespread predictions of chaos on road and rail networks and a city jammed with up to half a million visitors.

The desire to leave was proportionate to affluence, with fewer than six per cent of low income earners - those earning less than $30,000 (Aus) - planning to leave and 17 per cent of those in the middle income group from $30,000 to $130,000. The figure jumps to 41 per cent for those earning more than $130,000.

Of those intending to leave, 55 per cent planned to go overseas. The survey, of more than 500 people, found that almost 20 per cent of those in the host state of New South Wales had a negative attitude towards the games, while 56 per cent had a positive attitude and the remainder were neutral.

16 per cent of those surveyed said they would attend some aspect of the Olympics and three quarters of those had already bought their tickets. Nearly half of those who have already bought tickets plan to buy more.

A quarter of those planning to stay said they were likely to have family and friends stay with them.

For those who won't attend the Olympics, nearly 40 per cent gave high cost as the reason, followed by other commitments, too busy, too crowded or just not interested.

Officials say ticket sales have been slow in recent weeks, with some 150,000 tickets still available, following a fiasco over ticket sales and string of public relations disasters for games organisers. Many people have been put off by allegations of corruption concerning Olympic officials as well as persistent reports about drugs use and abuse.

US Trials: Australia's representative on the IAAF's Athletes' Commission yesterday questioned whether Michael Johnson and Maurice Greene withdrew from the US 200-metres Olympic trials final to avoid mandatory drug tests.

Johnson and Greene had been involved in a bitter war of words leading up to the race, but both failed to finish after suffering leg injuries. Simon Baker, who sits on the athletes commissions of the IAAF and Athletics Australia, told a Sydney radio station that the circumstances surrounding the 200-metres final "turned it into a farce".

"It just looked like a couple of guys who wanted to avoid scrutiny," said Baker, a race walker who represented Australia at four Olympic Games. "You start to wonder when you suddenly have two athletes of that calibre pulling out.

"You start to think maybe there's a bit of pressure, maybe they're starting to think they have to be a bit more circumspect in terms of if they had finished first, second or third, they would have been specifically up for a drug test."

Both Johnson and Greene were drug tested earlier in the US Olympic trials after winning the 400 metres and 100 metres respectively. All medallists at the Sydney Olympics will be drug-tested, in addition to the random testing program. Johnson is the 200-metres world record holder and Greene the 200-metres world champion.