Most smog checks take between 15 and 20 minutes. A smog test evaluates vehicle emissions to prevent excess air pollution. Smog is combination of carbon monoxide, hydrocarbons, nitrogen oxides, carbon dioxide and oxygen. Vehicle gas emissions are linked to global warming and pose health hazards.

The particulates from diesel are carcinogens that can cause respiratory, heart and life-shortening diseases.

Smog regulations are different in every state. Not every state requires a smog check for vehicles. A car that passes a smog test in one state may not pass a smog test in another state if it has more restrictive regulations. If a car fails the smog test, then the driver must get the car fixed and pass the test for it to be legal to drive again.