By 1890, electric streetcar lines were replacing horse-drawn ones in cities of all sizes, allowing the lines to be extended and fostering a tremendous amount of suburban development. They were often extended out to formerly rural communities, which experienced an initial surge of development, and then new residential corridors were created along the newly built lines leading to what had sometimes been separate communities. On side streets, the houses closest to the original streetcar line are often as much as ten to twenty years older than houses built further down the street, reflecting the initial surge and slow completion of a development.