Air analysis inside vehicles is a problem that can be interpreted from several perspectives. This research is oriented towards the perception of air quality within a car, regarding a situation of cars in stationary traffic. Carbon dioxide measurements were made using a Trotec Data Logger Air Quality CO₂ BZ30 machine inside different standing vehicles with up to five occupants, with and without circulating air. The perception of the air quality was measured on a Likert-type scale with seven levels on a sample group of 60 students. The results highlight, on the one hand, the conditions under which the CO₂ in the cabin air can reach concentrations which are, according to new data, considered to influence the cognitive capacity of occupants in the car, and on the other hand, they present a global assessment of the air quality in the vehicle when critical values of CO₂ have been reached. If the air exchange rates inside a car are low, this degrades the air quality in such a way that it affects the concentration and reactions necessary for safe driving without perceiving any discomfort that would put the drivers or the passengers on alert.