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.

Starting in the 1950s, the highway was reconfigured to bypass Mason and other communities, converting US 127 into a freeway from Jackson to the Lansing area by the mid-1970s.

[4] As a state trunkline highway, the roadway is maintained by the Michigan Department of Transportation (MDOT), and it includes approximately 162.6 miles (261.7 km) of freeway in two segments, the southernmost running between Jackson and Clinton counties, separated by a 16-mile-long (16 mi) gap from the northernmost segment between Gratiot and Crawford counties.

Near intersections with Manitou and Adams roads south of Addison, it crosses fully into Lenawee County.

The highway continues due north from Addison to an intersection with US 223's northern terminus in the northwestern corner of the county, where US 127 turns northwesterly.

The highway follows Meridian Road through the southern area of the county until the interchange with M-50 southeast of Jackson.

US 127 passes through Leslie with Churchill and Hull roads running parallel on either side of the freeway.

It is a four-lane divided highway with some local driveway access and cross traffic through at-grade intersections.

South of Ithaca, the highway crosses the Bad River and transitions back to a freeway for the remainder of its routing.

At the adjacent partial interchanges for Lincoln and State roads, two separate business loops depart from the freeway to run through the two cities.

The freeway crosses the Pine River while running between Alma and St. Louis before intersecting M-46 and the northern ends of the two business loops at another pair of adjacent partial interchanges.

It runs near the campus of Central Michigan University, crossing the Chippewa River in Mount Pleasant.

Mount Pleasant is also home to the Saginaw Band of Chippewa Indians and their tribal reservation.

[7][8] The business loop for Clare splits from the main freeway south of the city, and it is also signed to provide access to eastbound US 10 via Bus.

The freeway rounds Lake Shamrock north of downtown and intersects the joint northern end of two business loops.

The freeway passes between Little Long and Sutherland lakes north of Harrison before intersecting the northern end of the business loop.

[7][8] In 1919, the Michigan State Highway Department (MSHD)[a] signposted the highway system for the first time,[15] At the time, the original M-14 designation was assigned from the Ohio state line northward through Jackson, Lansing, Mount Pleasant, Clare, and Grayling.

Seven years later, the United States Numbered Highway System was created on November 11, 1926,[16] and in Michigan's initial assignments, US 27 replaced M-14 between Lansing and Cheboygan, while US 127 ran from Lansing southward through Jackson to the Somerset area where it turned southeasterly, replacing the former M-80 and M-34 through Adrian to Toledo, Ohio.

[10][11] MDOT petitioned the American Association of State Highway and Transportation Officials (AASHTO) for approval to remove US 27 from Michigan in 1999.

[12][13] In 2009, MDOT constructed Michigan lefts at several intersections in northern Clinton County to remove cross-street traffic.

[45] While there are no immediate plans to convert the section between St. Johns and Ithaca to freeway, MDOT continues to purchase parcels for right-of-way to be used for future upgrades.

[47] MDOT abandoned further study of I-73 after June 12, 2001, diverting remaining funding to safety improvement projects along the corridor.

[49] According to press reports in 2011, a group advocating on behalf of the freeway is working to revive the I-73 project in Michigan.

"[50] The Lenawee County Road Commission is not interested in the freeway, and according to the president of the Adrian Area Chamber of Commerce, "there seems to be little chance of having an I-73 link between Toledo and Jackson built in the foreseeable future.