Today, NASCAR drivers always wear their seat belts, no matter what. In the 1940s, seat belts were not the norm in racecars. Some drivers used rope or aircraft harnesses to hold themselves in place while racing. By the early 1960s, most racecars had lap belts, and shoulder straps were added.
For several years, five-point harnesses were the standard in NASCAR racing. The five-point harness, similar to those in child safety seats, was designed to keep the driver from “submarining,” or sliding out underneath the seat belt in during a head-on collision. In 2001, Dale Earnhardt was killed while wearing a five-point harness, so many drivers switched to a six-point harness in which belts are wrapped around each of the legs.
In 2007, TxDOT partnered with NASCAR to convince Texans to buckle up.
You can read more on the extensive equipment NASCAR drivers use to stay safe here.