As GIs returned home after WWII, they found a need for excitement and entertainment. Those were days when, other than the radio or a local movie theater, people were left to their own devices regarding how they spent their leisure time.
Thus, automobile racing really took off on many levels. The more professional types of short track racing, such as the "open cockpit" Sprint Cars and Midgets, had been established prior to the war, but became far more popular afterward. Most people could not afford to purchase these "state of the art" race cars. In addition, they were extremely dangerous, especially for anyone with no prior automobile racing experience. Numerous drivers started out in the more affordable but equally dangerous Track Roadsters. Many of these drivers, who showed enough skill, were hired to drive the Sprints and Midgets. That cost and danger brought about the advent of the Hard Top, and Jalopy. These were affordable and safer race cars. They could be built with a few tools, a cutting torch, and starting out with inexpensive older cars and junk yard parts.
All of these race cars were extremely popular through the late 1940s and into the 1960s. Then, with the exception of the Midgets, they began a transition to becoming one basic form of race car. The Track Roadster gave way to the "open cockpit" Sprint Car. The Jalopy/Hard Top evolved into the Modified or Super Modified which in many ways was similar to the Sprint Cars but with one major exception, a "full roll cage." However, in the mid to latter part of the1960's, due to numerous fatalities in open cockpit racing, there was a major outcry that "open cockpit" Sprint and Midget racing was far too dangerous and full "roll cages" were mandated.
Once full "roll cages" were added to the Sprint Cars, it was only a matter of time until the Modifieds and the Super Modifieds were absorbed into a "caged" Sprint Car class. Today, these cars are virtually unchanged with the exception that some associations allow large reverse air foils, "wings," on their Sprint Cars wile other associations still race the more traditional "non-winged" version.