highways, which are usually small, have low levels of traffic, and terminate at the limits of cities and towns. Each highway is designated with a label of between one and three letters, and are usually named sequentially, starting with Highway A and continuing to Z, then using double letters from AA to ZZ, and using triple letters if necessary, although this is not a requirement and there are plenty of exceptions. The various cities, towns, and villages of the state each maintain their own roads beyond this, servicing individual homes and businesses and connecting them to the other systems, although these are not typically referred to as highways. There are also several types and systems of roads in Wisconsin that are not part of any state or local highway system, and are not specifically constructed or maintained by the state Department of Transportation or by any local agency. Forest Highways are routes through National Forests, and are thus designated by the United States Forest Service. The Kettle Moraine Scenic Drive is a marked route that follows county and local roads past historical markers and attractions in the Kettle Moraine. It extends between Whitewater and Elkhart Lake. The Lake Michigan Circle Tour and the Lake Superior Circle Tour encircle Lake Michigan and Lake Superior, respectively. Minnesota State Highway 23 passes through Wisconsin in Douglas County for about before returning to Minnesota. The Yellowstone Trail was the first transcontinental automobile highway to be constructed through the upper tier of states in the United States. It was exempted from a state law banning privately-designated highways in 1917. History 19th century The many precursors to the state highway system predate the development of motorized vehicles by several decades, and the earliest even predate European settlement. For example, parts of the Native American trail connecting Green Bay to Sault Ste. Marie, Michigan, have now become US 41. In the early 19th century, wagon roads were created so that people and supplies could be transported from one settlement to another in days rather than weeks. Beginning in the 1830s, these routes were primarily improved and maintained by the United States military. These routes were gradually replaced by a decentralized network of both private plank roads and early territorial and state roads which, while created by the state government, were the responsibility of towns and villages to build and maintain. However, by the end of the 19th