Truck plates can be very confusing. I have been sorting these out for over 2 years, and still have a lot to learn. I will try by best to decipher types here.
From David L. Turner concerning Apportioned vs. P.S.C. types:
Apportioned and PSC plates came along for different reasons.
First about the apportioned. It's a base plate issued in one state but the monies collected for the plate are shared with other states which that vehicle travels in. SC-based trucks that do business in other states have to pay road taxes in those states, so the carriers pay SC and then SC splits that money with any state the carrier has traveled, which is the reason for the word 'apportioned' to be on the plates. Apportioned plates are purely for making sure a vehicle pays road taxes in every state the owner does business in. This is almost always a commercial vehicle. Its one thing to be a tourist traveling by private car on a pleasure trip but when using the highways to make money it becomes interstate commerce and the vehicle must help pay for the roads. The idea for apportioned plates was born in the late 1960s, and in 1974 about five states joined the newly formed International Registration Plan. In short, apportioned plates could be called IRP plates. They can be very expensive costing more than $1000 per year.
PSC plates: Every state has such a department although some states have different names for the same. The PSC is a regulatory agency having authority over several public utilities, telephone companies, power/electric companies, bus, taxi and trucking companies. Even though these companies might not be based out of SC, if they do business in SC then they become subject to the authority of the S.C.P.S.C. The PSC controls things like price rates and promotes good business in an effort to protect the public. It has nothing to do with the base plate fees associated with apportioned plates. PSC plates were on telephone trucks, taxicabs, UPS trucks, interstate buses as well as several other kinds of vehicles. They had them on the Ryder-owned trucks I drove which were leased to a private company making medical products. I don't understand why, because we were not a public utility providing services to the general public. There is much more to know about the PSC but that's about all I can say about it. I've read more about the Georgia PSC. They started in the 1870s to regulate the railroads. The department was originally called the Georgia Railroad Commission. Telephones and electricity came along giving more for the PSC to oversee so the name was changed to Georgia Public Service Commission. Trucking in Georgia became subject to the authority of the state PSC in late 1931. I have a 1933 so I wonder if it was the first issue. If the plate expired in 1933, it was likely issued in 1932 although I never found documented proof of this at the State archives.
Apportioned and PSC plates do not automatically go along together. Back in the days of PSC plates, a South Carolina truck could have an apportioned or just a regular truck plate. It just depended on how the vehicle was used and where it went. On a similar note, once there was the ICC - interstate commerce commission. With time and changes in the way government worked, authorities under the ICC were transferred to the DOT and now there is no more ICC. Its a deactivated department now.
A man could write a book on the history of trucking regulations.
-David L. Turner
Feb. 10, 2011