AS CITY POPULATIONS exploded in the 1800s, there was an urgent need for mass transportation. Trolleys were an early solution. The first trolleys, like buses, were horse-drawn, but in 1881, electric
streetcars appeared in Berlin, Germany. Electric streetcars soon became widespread throughout Europe and North America. Trolleys run on rails along a fixed route, using electric motors that receive power from overhead cables. As road networks developed, motorized buses offered a flexible alternative to trolleys. By the 1930s, they had replaced trolley systems in many cities. City buses typically have doors at both front and rear to make loading and unloading easier. Double-decker designs are popular, occupying the same amount of street space as single-decker buses but able to transport twice the number of people. Buses are also commonly used for intercity travel and touring. Tour buses have reclining seats, large windows, luggage space, and toilets. Recently, as city traffic has become increasingly congested, many city planners have designed new electric streetcar routes to run alongside bus routes as part of an integrated transportation system.
