The traffic accident has been one of the first ten death factors in Taiwan for past years. The published statistical data showed that the number of casualties has gradually increased, and indicated that the main cause of traffic accident was the negligence by drivers, nearly twenty percent of the total amount of accidents every year in Taiwan. Many published researches about driving safety pointed out that the negligence is usually caused by driver’s distraction and low level of alertness. In recent year, the Collision Warning System (CWS) providing visual, tactile and various audio signals to stimulate the driver’s sense of hearing for warning purpose has been developed to assist drivers for a safe driving. Therefore, this study investigated the effect of various audio signals in the collision warning system on driving performance using a driving simulator. The driving performances in perception-reaction time, speed and lane-departure amount were recorded. In this study the driver encountered a sudden cut-in of an event vehicle from an adjacent lane, braking in front and speeding up. The design levels were no alert, speech and beep sound in the collision warning system. Thirty male participants ranging from 20 to 30 years of age were recruited. The experimental results showed that a car with warning system could make the driver be on alert earlier and thus reduce the perception-reaction time. In addition, the beep sound induced a shorter perception-reaction time than the speech did. The driver would reduce speed when the vehicle equipped with warning system. With respect to the amount of lane-departure, the data showed that the position deviation was small as the driver did not change lane when the emergence happened in front.