Initially U.S cities were built according to a grid plan (grids being the most efficient means of urban planning at the time). This also made public transport e

Initially U.S cities were built according to a grid plan (grids being the most efficient means of urban planning at the time). This also made public transport easier. Grids however do not work well for cars. In response to increasing car ownership, T junctions were introduced to improve flow of traffic. The car also made it possible for people to live far from their place of work, thus the popularisation of suburbs. Other countries followed suit.