Mapping out NC's new vehicle emissions testing rules


If you live in North Carolina, chances are you have to get your vehicle inspected each year, before you can renew your license plate. The inspection consists of a safety portion, and in some counties an emissions portion. In the past, 48 of NC's 100 counties required the emissions portion of the inspection - but as of December 1, 2018 only 22 counties require the emissions test. Follow along to see which counties!

But before we get started, here's a picture to get you into the mood. This is my friend Thelma's car, getting worked on in her dad's shop. Do you think it will pass the NC emissions test? That's kind of a trick question - since it's 1995 or older, it doesn't require an emissions test (because most cars older than 1995 don't have the standard OBDII emissions monitoring). Can you guess what year, make, and model her car is? Here's a hint - think 'Supernatural'! (leave your guess in the comments section)

Now, let's get to that emissions testing data. The NC Department of Environmental Quality (DEQ) website provides a text list of the 22 counties that now require an emission inspection as part of their annual inspection. A text list is OK for some things (for example doing a text-search for a specific county), but it takes a lot of effort to read through the entire list, and you don't get to see the geographical trends in the data.

To augment the text list, I decided to also present the data in map form. Here's my map, showing the 22 counties that now require the emissions inspection (in blue). If you're familiar with NC, you'll notice it's mostly the counties around the larger metropolitan areas (with more vehicles and more pollution), most of which lie along our major interstates (I-85 and I-40). Click the map below to see the interactive version, with mouse-over text showing the county names, and you can then click on the counties to find a list of inspection stations in that county.

How does that compare to the 48 counties that required an emissions inspection before the change? I'm glad you asked! I created a map of those too. That's quite a change, eh!?!

A map adds a whole new dimension to the data, that a list of counties in a text paragraph just can't provide, eh? What other analyses (graphical, statistical, etc) do you think might be useful to apply to this data?

If you're a SAS programmer, and would like to see the code I used to generate my map, here's a link. This particular example uses some features not currently available in Proc SGmap yet, therefore I used Proc Gmap to generate the map.



About Author

Robert Allison

The Graph Guy!

Robert has worked at SAS for over a quarter century, and his specialty is customizing graphs and maps - adding those little extra touches that help them answer your questions at a glance. His educational background is in Computer Science, and he holds a BS, MS, and PhD from NC State University.

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  1. For extra credit, make one map with before _and_ after data, using a third color for counties that lost emissions testing in December. I guess you need a fourth color for "gained emissions testing", too, but I don't think there were any of those.

  2. Correct! In the early 2000's an inspector tried to fail my car on emissions testing, but then realized my car was too old!

  3. Rather than two maps,
    how about one map coded with three colors to show
    Belore and After 1 Dec 2018
    After Only
    Before Only

    • Robert Allison

      It all depends on "what question you're asking" of the data.
      In my case, my question was "which counties currently need an emissions inspection" (and I threw in the old map for comparison, since I had already created it a while back). 🙂

  4. We dont have annual inspections here in Illinois, but do have emission tests which must be taken at state facilities. Better get there when they open on Tuesday in the middle of the month or it isnt happening. Does NC have central emission stations? If so, could they be mapped? From a mapping perspective, I wonder how well emission testing stations are distributed among population centers. In Illinois, not distributed too well!

    • Robert Allison

      Ahh - that's interesting! Here in NC, most service stations get certified to do the annual inspections, and there are also some inspection-only places (no repairs, just inspections). I believe they are all privately run (rather than government run) here in NC.

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