mixture of primary and secondary roads, although some are freeways (for example, State Route 99 in California, which links many of the cities of the Central Valley, Route 128 in Massachusetts, or parts of Route 101 in New Hampshire). Each state has its own system for numbering and its own marker. The default marker is a white circle containing a black sans serif number (often inscribed in a black square or slightly rounded square), according to the Manual on Uniform Traffic Control Devices (MUTCD). However each state is free to choose a different marker, and most states have. States may choose a design theme relevant to its state (such as an outline of the state itself) to distinguish state route markers from interstate, county, or municipal route markers. See also List of longest state highways in the United States List of numbered highways in the United States Interstate Highway System, U.S. Highway System Missouri supplemental route County highway Highways in Australia Numbered street References Types of roads