Driving performance in cold, warm, and thermoneutral environments

Driving performance deteriorates at high ambient temperatures. Less is known about the effect of low ambient temperatures and the role of subjective aspects like thermal comfort and having control over the ambient temperature. Therefore, an experiment was constructed in which 50 subjects performed a road-tracking task in a cold (5 degrees C), a thermoneutral (20 degrees C) or a warm (35 degrees C) climate. All subjects had a heater/blower (H/B) which generated a fixed amount of heat/wind that could either be controlled or not controlled. In the cold climate, averaged leg skin temperature dropped to 18.5 degrees C and head skin temperature to 24.9 degrees C; the thermal comfort was rated between 'cold' and 'very cold'. In the warm climate, averaged leg skin temperature rose to 36.6 degrees C and head skin temperature to 30.8 degrees C; the thermal comfort was rated as 'hot'. Driving performance in the ambient temperature extremes decreased 16% in the cold environment and 13% in the warm situation. Having control over the local head temperature by adjusting a H/B affected neither thermal comfort nor driving performance. In agreement with the literature on priming effects, subjects who started with the no-control condition performed much better in all driving tasks because they were primed to focus on the driving task as such, rather than the complex combination of temperature controls and driving task. It can be concluded that a thermoneutral temperature in a car enhances driving performance and may thus positively affect safety. Using manual climatic controls in hot or cold cars may interfere with the driving task.