The waiting in a line of cars, the standing around in a glass-enclosed room smelling exhaust fumes and the frustration might not have been necessary.

A state audit released Wednesday questions whether Colorado’s vehicle- inspection program is really needed for air quality, noting that 93 percent of cars already pass the tests.

The report, released by the state auditor, says Coloradans would save nearly $30 million a year if more cars were allowed to forgo the tests instead of just those manufactured in the past four years.

The state set up the auto-inspection program in 1980, and it now operates in nine metro-Denver and northern Front Range counties. Cars made in 1981 or earlier must have annual emissions testing, while models from 1982 onward must be tested every other year. Vehicles manufactured in the past four years are exempt.

Vehicles that meet requirements after driving by roadside testing stations don’t have to go to bricks-and-mortar locations but still must pay the fee.

Cars that flunk the inspections must get repaired and pass another test before owners can renew their tags.

But as the audit showed, almost all vehicles now pass the emissions tests.

“Because of stricter vehicle manufacturing standards, air quality will continue to improve with or without the (inspection) program, as older vehicles are retired and replaced with newer, cleaner vehicles,” the audit says.

The test costs motorists $25 for 1982 and newer-model vehicles and $15 for older cars.

The audit recommends exempting 2001 and newer-model vehicles from the testing, which would save Coloradans $28.4 million a year in fees paid to test their cars. The audit also recommends replacing traditional testing for most cars, which involves running them on treadmills and recording emissions outputs, and instead using the on-board diagnostic computers that have been built into most vehicles since 1996.

The nine-county region is now in compliance with all federal air-quality rules except for ozone standards, for which it is classified as being in “marginal non-attainment.” The state in 2008 adopted a plan to meet air standards that includes, in addition to the auto inspections, controlling emissions on stationary sources such as power plants, oil refineries and oil and gas wells and by setting evaporation limits on gasoline.

The plan aims to bring the region in compliance with ozone standards by 2015.

But as revealed in the state audit, which was conducted with the help of private air- quality consultants, the vehicle-inspection program has only a tiny effect on ozone attainment. The audit found that the effect of the program was “a reduction in ozone concentration levels of 0.34 parts per billion, which represents 0.5 percent of the 75 parts per billion ozone national standard.”

The audit recommends revamping the inspection program or even considering its elimination.

The Department of Public Health and Environment, which administers the testing program, partially agreed with the recommendation to exempt more vehicles from testing. The agency said it was already proposing extending the exemption period to cars made in the past seven years, which would be the longest exemption period in the country.

“The department disagrees with the conclusion that the ongoing need for the (testing program) is uncertain,” department officials responded in writing to the audit. “The Denver Metro/North Front Range Area continues to be in violation of the federal ozone standards, and the (program) continues to lower ozone concentrations in the area.”

The department also partially agreed with the recommendation to use on-board diagnostic computers to test cars, saying it’s examining the idea but as there are no current federal standards for such testing it’s not “a currently viable strategy.”

Tim Hoover: 303-954-1626, thoover@denverpost.com or twitter.com/timhoover