their destinations. Many systems include railways that are elevated or at ground level. Subways are most useful in crowded urban areas, where heavy traffic often slows down travel by bus or car.
Many of the world's largest cities have or are planning extensive subway systems.
London was the first city to have a subway. Today, London has 10 lines that provide quick, cheap transportation to all parts of the city and suburbs. This subway system is often called the tube or the
underground. Some of its subway lines are so far underground that passengers go down on elevators. London's first underground passenger line opened in 1863. It used steam locomotives.
The first deep-level line opened in 1890 and had electric locomotives. All subways since then have
Several large cities in the United States have subway systems. Boston was the first American city to have a subway. It opened a line of 11/2 miles (2.4 kilometers) in 1897. The subway in New York
City is one of the largest in the world. A person can travel from the New Jersey shore, under the city, beneath two rivers, and into Long Island without seeing daylight. The first sections of New York's
subway were opened in 1904. In the United States, subways also operate in Atlanta, Baltimore, Chicago, Los Angeles, Philadelphia, San Francisco, and Washington, D.C. In Canada, subways operate in Montreal and Toronto.
There are three types of subways. One is called the open cut. The construction crew tears out the
streets and builds the subways in deep ditches. If two lines are going to cross, the crew digs one roadbed deeper than the other. If the crew lays a pavement or other type of cover over the cut in
the ground, the subway is called a cut and cover subway. The third form of subway, which is called
a tube, is constructed by boring through the earth at the desired depth without disturbing the
surface. This type of construction is for one or two tracks. The tunnels of an open-cut subway have
a rectangular shape. The tunnels of a tube subway are usually circular or semicircular. New York
City's subway is mainly rectangular. Much of the London subway is semicircular.