Several factors led to growth of the suburbs in the 1950s and have been mentioned in other answers, including the rapidly rising U.S. standard of living, in which pay steadily outstripped inflation, and the availability of low-cost mortgages, especially to veterans. A housing shortage in major cities, such as Manhattan, also led people to look outside of their "comfort zones" for housing, and the widespread availability of cars made living away from the streetcar or subway line a viable possibility.

Innovations in home construction that brought down the cost of the average house to an affordable level also contributed to the suburban exodus. Pioneers in this were the Levitt brothers, who brought mass production techniques to home building, enabling them to build 30 homes in a week. They used precut parts and built on concrete slabs, allowing them to construct a small starter home for just under $10,000. The first Levittown opened in 1947 on Long Island. These new housing developments, built by the Levitts and a host of other builders, were wildly popular, but generally excluded blacks, meaning that suburbanization remained largely a white phenomenon in the 1950s.

There were several causes of suburbanization in the 1950s. One of them was the availability of land in the suburbs. The land was less expensive to buy in suburban areas than in urban areas. As a result, people left the cities for the suburbs.

Another factor in the growth of suburbs was the building of highways. In 1956, the Federal Highway Act was passed. This led to the building of highways throughout the country. As more highways were built, it made commuting from the suburbs to the cities much quicker and easier.

A third factor leading to suburban growth was the fear people had of increasing crime in the cities. People believed suburbs were safer areas than the cities were. The suburbs also offered a more spacious area in which to live.

Finally, Americans were more prosperous in the 1950s. Incomes were rising, and more people owned their homes. Many veterans were able to get low interest loans from the GI Bill. They used these loans to build homes in suburban areas. All of these factors led to the growth of suburbs in the 1950s.

There were a number of causes of suburbanization. 

First, there was the building of new highways.  After World War II, the government started to build many new roads.  These roads allowed people to live in the new suburbs and to commute to the cities where they worked.

Second, there was the GI Bill.  The GI Bill helped cause suburbanization in a couple of ways.  First, it allowed many ex-servicemen to go to college.  By going to college, they came to be able to hold middle-class jobs that allowed them to afford the homes in the suburbs.  Second, the GI Bill provided loans to ex-soldiers.  These loans allowed them to buy the single-family houses in the suburbs.

Finally, the new prosperity in the US economy helped more and more people to be able to buy cars.  This was something that had not been possible for some years.  This allowed the people to live in the suburbs and drive to the cities.

Thus, the general prosperity of the 1950s, along with actions on the part of the government allowed suburbanization to occur.