The SF Bay area is getting a new smog check, where cars
must be inspected for condition of various engine, exhaust,
and fuel systems, and tailpipe emmissions are tested while
the car runs on a treadmill.
Most inspections will be performed at gas stations or car repair
businesses which may repair cars failing the inspection or test.
However, some cars are required to submit to a test-only facility.
It also sends a small percentage of cars to test-only smog stations,
which cannot make smog repairs. That provision is intended to cut
down on unscrupulous mechanics who fake successful smog tests to
avoid redoing repairs.
Explanation 2;
Smog Check II also requires 15 percent of vehicles to go to test-only
stations, which are not allowed to make repairs. If the cars fail,
then they go to a second shop for pollution-reducing repairs. The
system was meant to curb fraud -- either needless repairs or bribes
to pass smog-belching vehicles.