How many cars run with an underinflated tire, the problem a pressure sensor warns about?

NHTSA measured the tires of 11,530 U.S. vehicles in 2001 and found 27% of passenger cars and 33% of pickups, SUVs and vans had at least one tire underinflated by 8 psi or more, the fault tire pressure monitors were later required to warn about.

Cars, at least one tire27%

Trucks, at least one tire33%

Cars, two or more13%

Trucks, two or more20%

What it shows: Trucks, at least one tire is the largest at 33%; the smallest shown is Cars, two or more at 13%.

Source: NHTSA National Center for Statistics and Analysis, Tire Pressure Special Study: Vehicle Observation Data (DOT HS 809 317) · data from 2001