PASSENGERS on the MTR face trouble within two years, warn chiefs, and if the Lantau Line is not built by 1997 some way of controlling the number of passengers on stations is inevitable. In the worst scenario, some stations could be shut at street level to stop people getting in. Concern centres exclusively on the infamous Nathan Road corridor, between Mongkok, Yau Ma Tei and Jordan, the busiest part of the network. By 1995 more people will want to use it during the early-morning rush hour than it can cope with. ''1995 we see as a very difficult year,'' said the MTR's deputy operations director Roger Kynaston. ''At the moment we have 77,500 people using the Nathan Road corridor during the peak hour, and we are running 31 trains an hour for them. Next year we add a train, and our capacity rises to 80,000.'' But passenger numbers are expected to increase all the time, and the extra space will get used up sometime early in 1995. New improved signalling and train control systems will add another two trains per hour by 1996, bringing capacity to 85,000, but until then the system will have to cope by itself. The engineering work needed to install the new systems would cause problems all of its own, Mr Kynaston warned. ''We will be doing complex engineering work in the brief dead period in the middle of the night. ''This means in 1995 it is more likely the system will not come up in the morning, and we could see trains going through at slow speed.'' The extra capacity would again soon be used up, and by the summer of 1997 the Nathan Road corridor would once more be approaching capacity. At this point, only the new Lantau Line [part of the airport railway] could help. However, it is uncertain when the airport railway will be built since Britain and China have yet to agree on its financing. Overcrowding would mean the entire system could get log-jammed, warned Mr Kynaston. ''If a driver has to reopen the doors because someone was in the way that could cause a delay of seven, eight, nine seconds, which could double the dwell time, the time a train waits at a platform,'' he said. ''Dwell time is critical, even more important than the time a train takes between stations. While the train is at a station nothing else can happen behind it. If you add up nine seconds for each train, 34 trains an hour, it becomes a lot of time.'' In such a situation the MTR would face a choice of two ways of limiting passenger numbers, he said. ''We have physical controls, and price controls. ''We try to avoid having more than two train loads of people waiting at any one station. The Mass Transit Railway always reserves the right not to stop at a station if it is unsafe, but this causes almost as many problems as it solves. ''So our first step would be to stop the escalators. It would make it much slower for the passengers to get down to the platform. ''Then you can reduce the number of ticket gates that are open, to slow people down in the station concourse, or even shut the ticket gates down completely. ''If that is insufficient you can shut the station, putting somebody on the main gates. We can get some help from the police if we have to. ''The main criticism of all of these measures is that they are indiscriminate. You can't pick out those who are travelling in totally the opposite direction, people who are not contributing to the congestion. ''We don't want to cause inconvenience to passengers, we want them to get to their destination. ''That leaves the pricing mechanism.'' The MTR dropped the peak hour surcharge this year because it had enough trains, but it has not ruled out bringing it back. ''We could have some encouragement for people to travel outside the peak period,'' said Mr Kynaston. The Transport Department said it would do everything it could to provide alternatives to the MTR. ''We are encouraging the bus companies to run more air-conditioned buses along Nathan Road,'' said chief transport officer for public transport development Tsang Wing-hang. ''But people find the air conditioning of the MTR better in summer, and the MTR more reliable when it is raining. We try to provide bus lanes and bus priority measures, but there is always a bottleneck at the Cross Harbour Tunnel.'' The MTR reckons there is one sure solution to its problems. ''The system could carry three million people a day if they all came at different times,'' said the MTR's operations director Bill Donald. The solution was more flexitime and staggered working hours. ''It is such a simple answer to this problem. We have the capacity for much higher numbers throughout the day. ''If some companies and the Hong Kong Government had not already adopted flexible working hours we would be in much more difficulty.''