Improved technology has done more to reduce environmental harm than government emissions tests

See Blowup at the bogus checkpoint by James Bovard.

"An EPA air compliance inspector in Alaska admitted in 2012, “You’re just not finding a lot of dirty cars any more.” A Colorado government audit recently concluded that the “public need” for its emission testing regime was “uncertain” and recommended exempting all vehicles from model year 2001 onwards. (Maryland exempts only the two most recent model years.)

Improved technology by auto manufacturers has probably done a hundred times more to reduce environmental harm than government emission tests. According to University of Denver research engineer Gary Bishop, emission inspections “costs lots of money” but “does absolutely nothing to clean up the air.” Mr. Bishop, who has pioneered new methods of roadside sensor tests, found that auto emissions in Tulsa, Oklahoma, which has no emission testing, were no worse than in locales with strict testing regimes."

"Maryland, like many other states, has a massive, mandatory emission testing regime that relies on the Onboard Diagnostic (OBD) system in car dashboards. Regulators presume an illuminated Check Engine light proves that there is an emission violation. But there are plenty of reasons why the check engine light would go on aside from excessive emissions — such as a loose wire, a faulty sensor, or a computer glitch. When Ontario switched in 2013 from measuring tailpipe emissions to checking OBD readings, the percentage of vehicles that failed the tests soared by 60 percent."

"Federal, state, and local policies cause more air pollution than VEIP deters. Driving to the VEIP site, I had ample opportunity to cuss the pointless delays on the county’s main six-lane business corridor. Red lights are one of the biggest sources of air pollution around. But Montgomery County is raking in $4 million a year in fines from red light cameras, a strong deterrent to synchronizing the lights.

Maryland drivers are compelled to rely on fuel with 10 percent ethanol. Maryland has some of the worst smog problems in the nation and ethanol is notorious for increasing smog — especially in the summer. The Wisconsin Department of Natural Resources estimated that adding ethanol to gasoline does twice as much harm to air quality as auto emission testing prevents."