Transportation in Cities
Each decade has seen continual population growth within cities, and with it the demand
for improvements in urban transportation systems has increased. City transportation
began with horse-drawn carriages on city streets; these later traveled on steel tracks. They
were succeeded by cable cars, electric streetcars, underground electrified railroads, and bus
transportation. City travel by public transit has been largely replaced by the use of automobiles
on urban highways, although new rapid transit systems have been built in San
Francisco, Washington, D.C., and Atlanta