A、The train will stop automatically if no signal is sent from the command spot. B、Most of the control work is done by computers

The world’s first totally automatic railway has been built under the busy streets of London. The railway is called the Victoria Line, and it is part of the complete London subway railway. It was opened in 1969. This new line was much different from others.
    The stations on the other lines need a lot of workers to sell tickets, and to check and collect them when people board or leave the trains. Startling enough, the Victoria Line is very different from that old operating system. Here a machine checks and collects the tickets, and there are no workers on the platforms.
    There is only one worker on the train of the Victoria Line. The man usually just starts it. The train runs and stops automatically. It is controlled by electrical signals which are sent by the so-called "command spots". Each spot sends a certain signal. The train always moves at the speed that the command spots permit. If the command sends no signals, the train will stop by itself.
    Most of the control work is done by computers. The computers fix the trains’ speeds, and send the signals to the command spots. If one train stays too long at a station, the other trains will then automatically move slower. So there is no danger of accidents on the line.