The world’s first completely automatic railway has been built
under the busy streets of London. On this railway, the trains drive themselves,
and all the work is done by machines. This railway has seven "separate" lines,
which connect at various stations. Together they serve most parts of England’s
capital city. The people of London saw that this new line was
very different from the others. The stations on the other lines needed a lot of
workers. People are needed to sell tickets, and to check them. Others collect
tickets when people leave the trains. There are men and women on the platforms
(站台). They check that everything is all right. On the trains, too, there are
several workers. This is all different on the Victoria Line.
Here a machine checks and collects the tickets, and there are no workers on the
platforms. If a man wants to ask about the trains, he must use a special
telephone. What does the sentence "the trains drive themselves" mean
It means there are ______ working on the train.