Existing driver information systems (DIS) include navigation, radio, telephone, television etc. The addition of computer functions like internet or word-processing turns DIS into car computing devices (CCD), often called CarPCs. Due to the high mental and visual load of driving, solutions matching the human factors needs of the driving environment have to be developed.A usability study testing four different existing DIS was conducted. It is possible to transfer the results to future CCD. The visual channel should not be stressed by CCD. Applications running in car have to use acoustic and haptic channels for information transfer between driver and system.