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. Compartment temperatures are often raised voluntarily to 27°C in winter, and in air-conditioned vehicles in summer, to avoid discomfort due to cold draughts on certain body sections. Effective vehicle climate control thus contributes to road safety by optimising working conditions for the driver.