M-99 is maintained by the Michigan Department of Transportation (MDOT) like other state highways in Michigan. As a part of these maintenance responsibilities, the department tracks the volume of traffic that uses the roadways under its jurisdiction. MDOT's surveys in 2010 showed that the highest traffic levels along M-99 were the 32,262 vehicles daily north of Mount Hope Avenue in Lansing, on average; the lowest count was 2,300 vehicles per day between the state line and the M-34 junction. No section of M-99 has been listed on the National Highway System, a network of roads important to the country's economy, defense, and mobility.