On the east banks, M-57 runs along Main Street south along the river to a junction with Peet Road where it then turns east along the latter road out of town. The highway passes through more farm fields and through Layton Corners on the way to a junction with M-13 on the Saginaw–Genesee county line. At Montrose, M-57 crosses the Flint River, and a line of the Huron and Eastern Railway. Now running along Vienna Road, the trunkline meets I-75/US 23 west of Clio. As it enters town, it crosses a line of the Saginaw Bay Southern Railway. This segment of the highway passes through the northernmost suburbs of Flint, and this section is where the heaviest traffic levels along the whole highway are found. As part of its maintenance duties, the Michigan Department of Transportation (MDOT) tracks these traffic levels using a metric known as average annual daily traffic (AADT). This figure is a calculation of the average traffic volume for a segment of roadway on any average day of the year. In 2009, MDOT determined that an average of 22,280 vehicles used the section of M-57 through Clio daily. East of this area, the highway once again passes through rural agricultural lands on the way to its eastern terminus at M-15, one mile (1.6 km) north of Otisville. This terminal section of the trunkline had the lowest traffic levels in 2009 at 3,737 vehicles AADT. No section of M-57 has been listed on the National Highway System, a system of roadways important to the country's economy, defense, and mobility. History Previous designations In 1919, the Michigan State Highway Department signposted the highway system in the state for the first time. At that time, M-57 designation was originally used in Charlevoix County from Boyne Falls at M-13 (now US 131) through Boyne City and back to then M-13. That highway's number was changed to M-75 in 1926. By the next year, the number was then assigned to a state trunkline that connected between Quinnesec and the Wisconsin state line in the Upper Peninsula. This second iteration was short-lived as it was replaced by an extension of US 141 into Michigan. Current designation In 1930, M-57 was designated from M-66 (now M-91) near Langston to M-47 (now M-52) in St. Charles. By the mid 1936, the section between Ithaca and St. Charles was removed from the state highway system when