Within the safety test, there are 14 basic areas where the inspector checks for safety requirement standards. According to vehicletest, these areas are: visual overview, including vehicle registration, VIN number and license plate decal; brakes; exhaust system (muffler, blue or black smoke); suspension and steering (steering wheel, springs and shocks); horn; glass (including tinting), glazing and windshield wipers; rearview mirror; lights and reflectors; wheels and tires; fenders, bumpers and fuel tank; altered vehicle height; seat belts; airbags; and fuel tank cap.
Massachusetts has two types of emissions testing. On-board diagnostic (OBD) is the test for most vehicles. According to vehicletest, OBD tests are given to the following vehicles: model year 1996 and newer passenger cars, light trucks and SUVs; model year 1997 and newer light-duty diesel vehicles (8,500 lbs. or less); model year 2007 and newer medium-duty vehicles (8,501 to 14,000 lbs.); model year 2008 and newer medium-duty diesel vehicles (8,501 to 14,000 lbs.). The tests check that the vehicle's computer OBD system communicates properly with the inspector's analyzer. The OBD system in your vehicle must have completed enough self-checks to be ready for an emission check.
Snap acceleration opacity tests are for buses, trucks and heavy-duty vehicles that weigh more than 10,000 lbs. and are not equipped with OBD devices. An inspector will use an opacity meter to measure the smoke emitting from the exhaust pipe. Readings from the final three acceleration "snaps" are averaged to attain the reading, according to vehicletest. The final reading is then compared to the emission standard for the model year and type of vehicle. The darker the smoke, the higher the emission reading will be.
