IT is 8.39 am, the middle of the ''crush hour'' on the Mass Transit Railway. There are no seats left, and at this time most commuters don't worry about that. Getting on at all is the problem. ''It is so much trouble,'' says Jovy Tam Shuk-chai, 27. She wants to get from Shamshuipo along the Nathan Road corridor to Causeway Bay. But today, like most days, she starts by heading the wrong way. ''I often come one stop up the line to Cheung Sha Wan. It takes an extra five minutes, but at least I can get on.'' Getting on at Cheung Sha Wan is not easy. The queue is so long that by the time Ms Tam gets to the front the train is packed. She has to wait for the next one. And when her train reaches Mongkok anyone would say it was full. Stand in the middle and you cannot see the doors. The people waiting 20 deep at Mongkok don't care. They've already watched two trains go past, and they have to get to work. The doors swish open, and the wedge of anxious commuters presses on board. The MTR's platform assistants have to physically forcethe doors shut. ''Sometimes,'' says Roger Kynaston, the MTR's deputy director of operations, ''we have to pull people off the train to get the doors shut.'' This is the MTR's unhappy hour, 8.15 am to 9.15 am, in the Nathan Road corridor. Middle managers and secretaries, exchange floor dealers and hotel waiters, hurrying to work for the 9 am start, packed in 2,500 to a train, one train every 116 seconds. And would they have it any other way? ''I could go by bus. I used to a year ago, but it would take me almost an hour,'' says Ms Tam. Accounting manager Ng Wing-hong takes the MTR from Wong Tai Sin to Tsim Sha Tsui every day. ''It can get very crowded, and sometimes you have to wait two or three trains before you can get on.'' But he'll be on it again tomorrow.