Studies in the USA have attempted to define the right population for an identifiable neighbourhood. One factor is that neighbourhood inhabitants should be able to look after their own interests by organizing themselves to bring pressure to bear on town hall or local government. This means that families in a neighbourhood must be able to reach agreement on basic decisions. In practice, it is difficult for this to be done if more than 1,500 people are involved: some authorities put the figure at as little as 500 people. A survey in Philadelphia asked people which area they knew well; respondents limited themselves to a small area, usually two or three blocks around their house. One quarter of the inhabitants of an area in Milwaukee considered a neighbourhood to be an area no larger than a block (300 feet); and one half considered it to be no more than seven blocks.
Other researchers have found that the heavier the traffic in an area, the less people think of it as home territory. People feel that streets with heavy traffic are less personal than streets without, and so are the houses on such streets. American statistics suggest that a neighbourhood begins to deteriorate once it has a road with more than 200 cars per hour. On streets with 550 cars an hour, people visit their neighbours less and never gather in the street to meet and talk. Research in London also indicates that any street with more than 200 cars per hour, at any time, will probably seem 'major' and start to destroy the neighbourhood identity.