Marta/Emission testing is an unnecessary requirement for Sumner County TN and a poor excuse to make a couple extra tax dollars off of it’s residents. From an environmental standpoint, the majority of modern cars have advanced exhaust systems that eliminate almost all carbon emissions. This means that 99% of y’all have to take time out of your day to sit in a long line to pass a test you shouldn’t need to take. 
Now for a more serious note, if your car does not meet emission standards you are required to replace your catalytic converter/ whatever part your vehicle may need. Repairing these issues can cost upwards of hundreds, possible thousands of dollars depending on the vehicle. If these issues are not fixed and your vehicle continues to not pass, you are not able to renew your vehicle tags. All in the name of the “environment.” 
For someone who is struggling financially, this is incredibly inconvenient and hurts lower income families who rely on a vehicle that may or may not be able to be renewed or registered. 
Last, car/truck enthusiasts or literally anyone who wants to delete their catalytic converters for sake of performance or sound should have the right to. 

That’s all I have to say.