I was learning about the building of rally cars and I read about the importance of a roll cage in these cars. Road cars that normal people like myself drive don't have these and I know most these aren't going used under the same conditions as a rally car would be, but there are a lot of road cars that are flipped or get in bad accidents. Rally car drivers who get into some of the same accidents have a greater chance of walking away from the crash. The purpose of the roll cage is to protect the driver, so why aren't they be installed into road cars?