In an early-1970's document (https://books.google.com/books?id=cpQ1AQAAMAAJ&pg=PT11&lpg=PT11&dq=illinois+fap+411&source=bl&ots=BH8Kd1GQBy&sig=ACfU3U0uqT1-nfiqUi6CXaYVW0RXBkvu3g&hl=en&sa=X&ved=2ahUKEwjc6ImU7ZnhAhVSPq0KHVqqDPMQ6AEwAXoECAgQAQ#v=onepage&q=illinois%20fap%20411&f=false) about a proposed north-south freeway (Illinois FAP 411) that would have bypassed Danville, Illinois and surrounding areas to the east, but was never actually built, the section about the would-have-been Georgetown, Illinois exit (referred to as the "Georgetown Connection" in the document), which would have intersected with Vermilion County Highway 23, locally known as Mill Road and connects Georgetown with Cayuga, Indiana and IN-234, noted that Mill Road/C.H. 23 was functionally classified as an "Area Service highway" at that time. The Area Service functional road classification does not exist in the modern functional road classification system (https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm) that is used in the United States nowadays; Mill Road/C.H. 23 is classified as a Major Collector under the modern system (http://idot.illinois.gov/Assets/uploads/files/Transportation-System/Maps-&-Charts/Five-Year/FCCounty/FC%20County_Vermilion.pdf).
Did the Area Service road classification actually exist at one time, and, if so, when was it phased out of the functional road classification system?
http://www.co.la-paz.az.us/DocumentCenter/View/116/Public-Works-Standards---Volume-I-PDF page 14 shows it's higher than arterial.