M-21 is an east–west state trunkline highway in the US state of Michigan connecting the cities of Grand Rapids and Flint. The highway passes through rural farming country and several small towns along its course through the Lower Peninsula. Following the course of a handful of rivers, M-21 also connects some of the state's freeways like Interstate 96 (I-96), US Highway 127 (US 127) and I-75. The highway is used by between 1,700 and 36,000 vehicles daily.
M-99 is a north–south state trunkline highway in the Lower Peninsula of the US state of Michigan. It runs from the Ohio state border, where it connects to State Route 15 (SR 15), north to Lansing, where it terminates at a junction with Interstate 496 (I-496). The highway mainly serves local communities along the route as it passes through farm lands in the southern part of the state. One short segment, in Jonesville, is routed concurrently with US Highway 12 (US 12). The segment within Lansing follows Martin Luther King Jr. Boulevard.
M-25 is a state trunkline highway in the US state of Michigan. The route follows an arc-like shape closely along the Lake Huron shore of the Thumb in the eastern Lower Peninsula between Port Huron and Bay City. It serves the lakeshore resorts along Lake Huron and Saginaw Bay and generally lies within sight of the lake and the bay. All is surface road and generally scenic, except for the freeway segment near the junction with Interstate 75 (I-75) and connection into the US Highway 10 (US 10) freeway.
M-27 is a north–south state trunkline highway in the extreme north of the Lower Peninsula of the US state of Michigan. The trunkline runs between Interstate 75 (I-75) just north of Indian River and Cheboygan, where it meets US Highway 23 (US 23) near Lake Huron. It remains as a relic of the old US 27 which disappeared north of Grayling after being supplanted by I-75, which lies close to old US 27 between Grayling and Indian River.
H-63 is a county-designated highway (CDH) in the Upper Peninsula of the US state of Michigan. The highway parallels the Interstate 75 (I-75) corridor between St. Ignace and Sault Ste. Marie. The road is called Mackinac Trail after the Upper Peninsula branch of an Indian trail used before European settlers reached the area. Originally, the roadway was built as a section of US Highway 2 (US 2) before being added to the CDH system in the 1970s.
M-76 is a former state trunkline highway designation in the Lower Peninsula of the US state of Michigan. The highway's designation was decommissioned when the last section of it was converted to freeway as a part of the present-day Interstate 75 (I-75). At that time, M-76 extended from US Highway 23 (US 23) near Standish northwesterly to I-75 south of Grayling. Two sections of the route followed freeways with a two-lane highway in between to connect them. The former routing of M-76 through West Branch before that city was bypassed was initially redesignated Business M-76. The highway itself ran through mixed fields and forests bypassing several other towns in the region.
M-33 is a north–south state trunkline highway in the US state of Michigan that runs from Interstate 75 (I-75) at Alger in Arenac County north to M-27 near Cheboygan. In between, the trunkline runs through rural sections of the northeastern Lower Peninsula including state and national forest areas. M-33 connects to a handful of parks and crosses several of the rivers in that section of the state. It runs concurrently with three other state highways, sharing pavement to connect through several small communities of Northern Michigan.
M-72 is a state trunkline highway in the US state of Michigan, running from Lake Huron to Lake Michigan across the northern part of the Lower Peninsula. The highway connects M-22 in Empire with US Highway 23 (US 23) in Harrisville. It is one of only three Michigan state trunklines that cross the Lower Peninsula, shore to shore. In between, M-72 runs across Northern Michigan woodland, agricultural areas of the Leelanau Peninsula near Traverse City, and the Au Sable River watershed. The trunkline also provides access to Camp Grayling, a National Guard training facility near the city of the same name. Traffic levels along the highway vary from approximately 800 vehicles a day on the east end to over 32,000 vehicles near Traverse City.
US Highway 27 (US 27) is a part of the US Highway System that now runs from Miami, Florida, to Fort Wayne, Indiana. In the US state of Michigan, it was a north–south state trunkline highway that entered the state south of Kinderhook and ended south of Grayling. Its route consisted of a freeway concurrency with Interstate 69 (I-69) from the state line north to the Lansing area before it followed its own freeway facility northward to St. Johns. From there north to Ithaca, US 27 was an expressway before continuing as a freeway to a terminus south of Grayling.
Interstate 75 (I-75) is a part of the Interstate Highway System that runs north–south from Miami, Florida, to Sault Ste. Marie in the Upper Peninsula of the US state of Michigan. I-75 enters the state from Ohio in the south, north of Toledo, and runs generally northward through Detroit, Flint, and Bay City, crosses the Mackinac Bridge, and ends at the Canadian border in Sault Ste. Marie. The freeway runs for approximately 396 miles (637 km) on both of Michigan's major peninsulas. The landscapes traversed by I-75 include Southern Michigan farmland, northern forests, suburban bedroom communities, and the urban core of Detroit. The freeway also uses three of the state's monumental bridges to cross major bodies of water. There are four auxiliary Interstates in the state related to I-75, as well as nine current or former business routes, with either Business Loop I-75 or Business Spur I-75 designations.
M-18 is a north–south state trunkline highway in the Lower Peninsula of the US state of Michigan. It runs for 77.530 miles (124.772 km) through the central region of the state connecting US Highway 10 (US 10) near North Bradley with M-72 in rural Crawford County near the community of Luzerne. In between, the roadway connects several smaller communities while running through woodlands in both state and national forest areas. Two segments of M-18 run along sections of county boundaries, and one part of the highway forms a component of the business loop for the village of Roscommon.
Interstate 69 (I-69) is a part of the Interstate Highway System that will eventually run from the Mexican border in Texas to the Canadian border at Port Huron, Michigan. In Michigan, it is a state trunkline highway that enters the state south of Coldwater and passes the cities of Lansing and Flint in the Lower Peninsula. A north–south freeway from the Indiana–Michigan border to the Lansing area, it changes direction to east–west after running concurrently with I-96. The freeway continues to Port Huron before terminating in the middle of the twin-span Blue Water Bridge while running concurrently with I-94 at the border. There are four related business loops for I-69 in the state, connecting the freeway to adjacent cities.
There are currently eight business routes of Interstate 94 (I-94) in the US state of Michigan. These business routes connect I-94 to the downtown business districts of neighboring cities. Seven of the eight routes are business loops which bear the Business Loop I-94 designation while one is a business spur that bears the Business Spur I-94. These loops are former routings of I-94's two predecessors in Michigan: US Highway 12 (US 12) or US 25. The westernmost BL I-94 runs through the twin cities of Benton Harbor and St. Joseph along the former routing of US 12 and US 31/US 33 that now includes a section of the Lake Michigan Circle Tour in the state. The loops in Kalamazoo, Battle Creek, Marshall, Albion, and Jackson were also formerly segments of US 12 which were later designated as separate version of Business US Highway 12 through their respective cities before becoming BL I-94s in 1960. The BL I-94 in Kalamazoo was converted into BS I-94 in 2019. The route of the business loop through Ann Arbor was previously US 12 and then later M-14 before receiving its current moniker. The BL I-94 through Port Huron was previously US 25 and then Business US Highway 25.
There are currently four business routes of Interstate 69 (I-69) in the US state of Michigan. Designated Business Loop Interstate 69, they are all former routings of I-69's predecessor highways, US Highway 27 (US 27), M-78 or M-21, in whole or in part. The BL I-69 in Coldwater and the one in Charlotte were both parts of US 27 before the freeway bypassed those two cities in 1967 and the early 1970s, respectively. The BL I-69 through Lansing and East Lansing was previously part of M-78 and Temporary I-69 until it was redesignated in 1987. Before 1984, the loop in Port Huron was originally part of M-21 and was initially a business spur numbered Business Spur Interstate 69. It was later redesignated when it was extended to run concurrently with that city's BL I-94 which was originally part of I-94's predecessor, US 25. Each business loop follows streets through each city's downtown areas and connects to I-69 on both ends, giving traffic a route through the downtown and back to the freeway.
There have been nine business routes for Interstate 75 in the US state of Michigan. Numbered either Business Loop Interstate 75 or Business Spur Interstate 75 depending if they are a full business loop or a business spur, these highways are former routings of I-75's predecessor highways in the state. They were designated as I-75 was completed through the various areas of Michigan. The business loop in Pontiac runs through that city's downtown along a section of Woodward Avenue and a segment of roadway formerly used by M-24. The former Saginaw business loop was once a part of US Highway 23 (US 23), as was most of the original Bay City business loop. The roadways that make up the business loops in West Branch and Roscommon were previously part of M-76, I-75's predecessor through that part of the state. In Northern Michigan, the Grayling and Gaylord BL I-75s were part of US 27, and the two business routes in St. Ignace and Sault Ste. Marie in the Upper Peninsula of Michigan were part of US 2. A tenth business route, a loop through Indian River has been proposed. Each of the business loops connects to I-75 on both ends and runs through their respective cities' downtown areas. The two business spurs only connect to I-75 on one end and run into the appropriate downtown.
US Highway 10 (US 10) is a part of the United States Numbered Highway System that runs from West Fargo, North Dakota, to the Lower Peninsula of the US state of Michigan. The highway enters Michigan on SS Badger, which crosses Lake Michigan between Manitowoc, Wisconsin, and Ludington. As the highway crosses the state, it is a two-lane undivided highway between Ludington and Farwell and a freeway from Farwell east to the highway's terminus in Bay City. US 10 runs concurrently with US 127 in the Clare area along a section of freeway that includes a welcome center in the median. Outside of the Clare and Midland areas, US 10 runs through rural areas of West and Central Michigan in a section of the Manistee National Forest as well as farmfields.
US Highway 127 (US 127) is a part of the United States Numbered Highway System that runs from Chattanooga, Tennessee, to the Lower Peninsula of Michigan. In Michigan, it is a state trunkline highway that runs for 212.2 miles (341.5 km), entering from Ohio south of Hudson and ending at a partial interchange with Interstate 75 (I-75) south of Grayling. US 127 is the primary route connecting Lansing and Central Michigan to Northern Michigan and the Mackinac Bridge. From the south side of Jackson northerly, it is mostly a four-lane freeway. A notable exception is a 16-mile (26 km) stretch from north of St. Johns to just south of Ithaca, where the highway is built as an expressway and speed limits are lower. South of Jackson to the state line, the trunkline is a two-lane, undivided highway with access from adjacent properties.
US Highway 25 (US 25) was a part of the United States Numbered Highway System in the state of Michigan that ran from the Ohio state line near Toledo and ended at the tip of The Thumb in Port Austin. The general routing of this state trunkline highway took it northeasterly from the state line through Monroe and Detroit to Port Huron. Along this southern half, it followed undivided highways and ran concurrently along two freeways, Interstate 75 (I-75) and I-94. Near the foot of the Blue Water Bridge in Port Huron, US 25 turned north and northwesterly along the Lake Huron shoreline to Port Austin.
There have been 10 business routes of US Highway 127 in the state of Michigan. The business routes are all sections of state trunkline highway that run through the central business districts of their respective towns connecting them to the mainline highway outside of those downtown areas. These various business routes were formerly part of the routing of US Highway 127 (US 127) or its predecessor in Central Michigan, US 27, before the construction of highway bypasses. The southern two, in Jackson and Mason were previously parts of US 127, while seven of the northern eight were originally part of US 27, a highway which was replaced on its northern end by US 127 in 2002. The business loop through Alma was once numbered US 27A.
M-72 in Grayling 
I-75 / BL I-75 near Grayling
