Allison automatic transmissions have higher ratings and new designations to better indicate intended duties. The Rugged Duty Series (RDS) is for vocational trucks, like dumps and mixers, while the Highway Series (HS) is for freight-hauling trucks that stay on pavement. RDS and HS models include the 1000, 2000, 3000 and 4000 series. RDS family includes nine models and HS has seven models, many with optional retarders and PTO provisions.