Cullum Owings Large Truck Safe Operating Speed Act of 20 21 This bill directs the National Highway Traffic Safety Administration (NHTSA) to implement regulations to require (1) all new commercial motor vehicles with a gross weight of 26,001 pounds or more to be equipped with speed-limiting technology; (2) any existing speed-limiting technology already installed in such vehicles manufactured after December 31, 1992, to be used while in operation; and (3) the speed-limiting technology to be set to a maximum speed of 65 miles per hour, or 70 miles per hour with the use of adaptive cruise control systems and automatic emergency braking systems. The NHTSA must also prescribe performance standards for speed-limiting technologies, automatic braking systems, and adaptive cruise control systems that reduce or mitigate collisions at speeds of not faster than 70 miles per hour.