One of my favorite sightings on the roads of Washington state is this special license plate, number 99999-Z, which was frequently parked near the University of Washington campus in the early 2000s.  Sometime in 2002 I grabbed my old digital camera and got a photo.

This was the very last number issued in the original commercial vehicle format that began in 1987 with the introduction of the Mt. Rainier / Centennial Celebration baseplate.

When the mountain design debuted in 1987, it also established all-new licensing series for most vehicle classes.  Commercial vehicles were given a 12345-A format of five numbers and one letter, starting with 00000-H.  Earlier letters were not used, as they conflicted with other types that that were in use.

As plates were issued, letter suffixes increased through the alphabet.  The letters I, K, M, O, Q, and S were skipped because of legibility concerns or conflicts with other licensing schemes.

By early 1995, having issued 100,000 sets of plates in each of the H, J, L, N, P, R, T, U, V, W, X, Y, and Z series, the state ran out of number combinations.  After 99999-Z had been issued, a new format for commercial plates was implemented, this time in an A12345B format.

The new series commenced with plate A00000A.  After A99999A was issued, the last letter advanced to B, with A00000B coming next.  It took about 11 years until the last plate in the A-series was issued (A99999Z), at which point the first letter advanced to B00000A and the count-up started over.

By mid-2022, the A, B, and C prefixes had been exhausted and commercial plates began appearing with a D in the first position.  Given that it took approximately 27 years to churn through three letter prefixes, this licensing format should be in place for a very long time.