Cov qhov rooj hluav taws hauv tsev feem ntau hu ua qhov rooj hluav taws, uas yog qhov kawg ntawm kev hloov pauv ntawm cov qhov rooj ntoo zoo tib yam, lub qhov rooj tiv thaiv tub sab thiab lub qhov rooj tiv thaiv tub sab. Qhov hluav taws kub txwv lub sij hawm ntawm Class A qhov rooj hluav taws tuaj yeem ncav cuag 1.5 teev, thiab qhov hluav taws kub txwv lub sij hawm ntawm Class B qhov rooj hluav taws yog 1 teev.