Infrasound (IS) in cars is quite strong and may be responsible for health effects. This paper presents measurements and simplified mechanisms for the production of IS in vehicles. Four mechanisms are proposed:
1. turbulence from the moving vehicle or other traffic, infusing through the vents,
2. flexing of the body causing volume changes,
3. acceleration of the vehicle, causing an inertial reaction from the enclosed and external air,
4. pressure variations due to altitude changes.
The acoustic pressure from these mechanisms can be simplified by the fact that IS wavelengths are much larger than the size of the vehicle. Measurements are interesting and analyzed to elucidate the acoustic contribution of each mechanism.