By 1900, only a short stretch of the Detroit–Howell Plank Road was still made of planks; most of the other plank roads had been converted to gravel by this time. On May 13, 1913, the Michigan Legislature passed the "State Reward Trunk Line Highway Act" (Public Act 334 of 1913) that created the original state highway system. In that act, Grand River Avenue between Detroit and Grand Rapids was included as Division 9 of the system. The state highways were signposted starting in 1919, and on the first maps published on July 1 of that year, the Michigan State Highway Department (MSHD) had applied the M-16 number to Grand River Avenue across the state between Grand Haven and Detroit. M-16 was rerouted in the Lansing area in 1925, running along Grand River Avenue from Grand Ledge to East Lansing. The former routing through Downtown Lansing on Michigan Avenue became part of M-39 and the section north of Grand Ledge was eventually redesignated M-100. A second realignment moved M-16 to follow Grand River Avenue from Ionia through Ada. The former alignment became a part of M-21. On August 7, 1926, the state completed paving on M-16, opening it to traffic as "the first paved highway across the state".