During summer season people typically drive their vehicles by setting air conditioning system in recirculation mode to maximize cooling. Carbon dioxide exhaled by occupants remains within the cabin during operation in recirculation mode. The concentration of carbon dioxide starts increasing in the cabin. The CO2 that is inhaled by the occupants goes into their blood stream that negatively affects occupant's health. ASHRAE Standard 62 specifies the safe levels of carbon dioxide in conditioned space for humans. The CO2 concentration limit per ASHRAE is 700 ppm over the ambient conditions on a continuous basis. Current global average ambient concentration level of CO2 as of April 2017 (NOAA, 2017) is approximately 407 ppm. Hence, if the CO2 concentration exceeds approximately 1100 ppm inside of a home or a vehicle cabin, then we must introduce outside air into the home or vehicle cabin to reduce the CO2 concentration. In a recent investigation (Mathur, 2017; Atkinson et. al., 2017), the author had developed a model to predict cabin carbon dioxide concentrations as a function of time, number of occupants, vehicle speed, body leakage characteristics, occupant lung capacities and concentrations of the carbon dioxide coming out form occupant's mouth, blower position and vehicle age. The developed model was validated by the author for mid-sized vehicles (vehicles from D-segment). The simulated data was within ±11.5% of the experimental data. In this investigation, the author will present simulated results for vehicles from B & C segments and SUVs. The effect of the cabin volume is significant on the rate of build-up cabin carbon dioxide concentrations. Experimental tests have also been planned with small cars. Detailed results will be presented in the paper. REFERENCES 1. ASHRAE/ANSI, Standard 62-1999, Ventilation for acceptable indoor air quality, American Society of Heating Refrigerating and Air Conditioning Engineers., Inc., Atlanta, GA, 1999. 2. http://www.esrl.noaa.gov/gmd/ccgg/trends/ 3. Mathur, G.D. 2017. Development of a Model to Predict Build-Up of Cabin Carbon Dioxide Concentrations in Automobiles for Indoor Air Quality, SAE Paper # 2017-01-0163. 4. W. Atkinson, W. Hill, Mathur, G.D. 2017. The Impact of Increased Air Recirculation on Interior Cabin Air Quality, SAE Paper # 2017-01-0169.