Cognitive load and detection thresholds in car following situations: safety implications for using mobile (cellular) telephones while driving

This study was aimed at investigating drivers' ability to detect a car ahea d decelerating, while doing mobile phone related tasks. Nineteen participan ts aged between 20 and 29 years, (2000-125 000 km driving experience) drove at 80 km/h, 50 m behind a lead car, on a 30 km section of motorway in norm al traffic. During each trial the lead car started to decelerate at an aver age of 0.47 m/s(2) while the participant either looked at the car in front (control), continuously dialed series of three random integers on a numeric keypad (divided visual attention), or performed a memory and addition task (non-visual attention). The results indicated that drivers' detection abil ity was impaired by about 0.5 s in terms of brake reaction time and almost 1 s in terms of time-to-collision, when they were doing the non-visual task whilst driving. This impairment was similar to when the drivers were divid ing their visual attention between the road ahead and dialing numbers on th e keypad. It was concluded that neither a hands-free option nor a voice con trolled interface removes the safety problems associated with the use of mo bile phones in a car. (C) 1999 Elsevier Science Ltd. All rights reserved.