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Effective control of the micro-climate in a vehicle has traditionally been regarded as being important for comfort, but in the absence of experimental results showing any measurable negative effects of compartment temperatures in or near the comfort zone on driver performance, it has not been regarded as a factor in road safety. The authors have recently reported new results demonstrating an unexpectedly large negative effect on driver vigilance at 27°C, in comparison with 21 °C, in a moving vehicle: drivers missed 50% more of the signals presented in the first hour at the moderately raised temperature, and response times were 22% slower on average. These results provide powerful arguments for regarding not only air-conditioning, but also automatic temperature control, as safety features. Compartment temperatures in vehicles without these features often exceed 27°C due to solar and engine load, even at ambient temperatures well below 20°C.

By simulating in detail the dry heat loss of the human body, using a clothed, fuil-size thermal manikin whose 17 sections maintain a “skin-temperature distribution” identical with that of a human occupant in thermal comfort, the effect of the vehicle microclimate on sectional heat loss can be rapidly and accurately measured. The VOLTMAN system is based on a digital process-control computer capable of monitoring all relevant physical quantities in the vehicle as well as controlling the manikin. It can be rapidly installed in a standard vehicle, using the existing 12-volt power supply. Extensive field trials in the Arctic areas of Sweden and in Death Valley, California, have already demonstrated its utility and reliability under extremes of cold and heat. As the manikin is maintained at constant temperature it can achieve a new heat-flow equilibrium within a few minutes of a change in the microclimate, permitting a rapid rate of data aquisition.