In its early development in the UK in the 1930s, traffic calming was based on the idea that residential areas should be protected from through-traffic. Subsequently, it became valued for its ability to improve pedestrian safety and reduce noise and air pollution from traffic.
For much of the twentieth century, streets were designed by engineers who were charged only with ensuring smooth motor vehicular traffic flow and not with fostering the other functions of streets. Traffic calming initiatives have grown to consider other design functions as well. For example, it has been shown that car traffic severely impairs the social and recreational functions of public streets. The Livable Streets study by Donald Appleyard (1981)[2] found that residents of streets with light traffic had, on average, three more friends and twice as many acquaintances as the people on streets with heavy traffic which were otherwise similar in dimensions, income, etc.
Source: https://en.wikipedia.org/wiki/Traffic_calming