To allow for a uniform classification and easy comparison of car rental prices, the Association of Car Rental Industry Systems and Standards (ACRISS) has developed the ACRISS Car Classification Code coding system. This describes the size, door count, gearbox type (manual/automatic) and whether the car is air-conditioned, encoded into four letters. Additional classifications based on seat numbers and trunk volume were also set by the Belgian Rent a Car association in order to provide a unified system for assessing the car types in online reservation systems such as Amadeus or Argus.
Source : Car rental
