There is a code section listing the pass/fail limits for the roadside emissions testing:
law.lis.virginia.gov
(It's worth noting that they test for NOx, CO, and HCs, which are invisible--so you can fail one of these tests even if you aren't "rolling coal").
And, as I've stated previously, if your vehicle fails one of these, it will be subjected to ASM dyno testing, not just an OBD-II inspection. If for some reason it can't be given an ASM dyno test, then it will get a 2-speed idle test.
Them folks at DEQ are a little smarter than some give them credit for, and they are fully aware that a vehicle can be "tuned" to disable OBD-II monitors.
And the whole reason for roadside emissions monitoring is PRIMARILY to gauge the effectiveness of the mandatory emissions testing. Allowing someone to skip an emissions test is a secondary benefit. (And, worth noting, that the law states that a random 2% of the vehicles that pass roadside test are still required to get a test at a shop. And some vehicles, depending on make and model, are ALWAYS required to get a test at a shop, even if they pass the roadside test. I'd love to see what makes and models these are but all you can do is input a VIN to find out if that vehicle is one of them...)
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- The Commonwealth of Virginia applies a Vehicle Emissions Index (VEI) to determine the cleanest overall group of vehicles and their eligibility for RAPIDPASS. The VEI is an automated calculation based on the emissions test history of a particular Year, Make, and Engine Size. The VEI is updated quarterly and can range from a VEI score of 1 to 100. A lower VEI represents a vehicle that is expected to run cleaner than a vehicle with a higher VEI. Vehicle groups identified with a VEI exceeding the limit are not eligible for a RAPIDPASS. On the home page, click on VEI Lookup to use the VEI Lookup tool."