Maine's state classifications are the states functional classifications which don't exactly line up 1:1 with OpenStreetMap's highway classification hierarchy and its definitions. For example, a road identified as a Principal Arterial by functional classification varies between Interstates, various other freeways and expressways, and other roads identified as important such as  thoroughfares through major cities, airport/seaport access roads, and rural highways connecting smaller towns, etc. There are many inconsistencies that come with this data that makes it not useful in the scope of OSM. For instance, why should a trunk road end at Gateway Center Drive, a small dead-end road with a couple warehouses and a park & ride in Trenton, miles after it passes through a major highway junction in Ellsworth and before it reaches the bustling tourist destination of Bar Harbor? My concern isn't exactly that these trunk roads dead-end at small towns/lesser roads, but rather that this information is irrelevant to the average Joe who isn't in the loop with FHWA jargon using OSM as a map to get around. What the road connects to and lesser details like traffic data, speed limits, physical construction, etc. are more useful in this case.