NASCARs most significant safety improvements have come in the wake of major crashes. Restrictor plates were added to cars engines at Talladega and Daytona after Bobby Allisons scary crash. Head and neck restraints became mandatory in the wake of Dale Earnhardts fatal crash in the 2001 Daytona 500. Energy-absorbing SAFER barriers were added to inside walls and other unprotected barriers in the wake of violent wrecks that injured Denny Hamlin and Kyle Busch less than two years apart.