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M-22 & M-109 junction route signage in Glen Arbor, Michigan
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M-51 Route Marker On to Next Route:
Southern Terminus:    Indiana state line (connection w/IN SR-933) five miles south of downtown Niles
Northern Terminus:    I-94 at Exit 56 west of Paw Paw
Length: 40.406 miles
Maps: Route Map of M-51
Niles Area Trunklines Map, 2010–
Notes: In April 1998, M-51 was extended by five miles to head southerly from Niles via the former routes of BUS US-31 (S Eleventh St) and US-33 to the Indiana state line in order to fill the void left when US-33 was decomissioned in Michigan. The South Bend Tribune featured a photo of the crew changing some former US-33 sign assemblies on Tuesday, April 7, 1998, as well as an article on the "confusion" the change has caused on Thursday, September 17, 1998. Interesting to note, however, the "confusion" involves not only the general public, but also the Tribune itself! In articles, M-51's previous designation between Niles and the Indiana state line, US-33, is never mentioned and they maintain Eleventh St south of US-12 (or as they call it, "Bypass 12"... ahem!) was designated as BUS US-31. Since 1926, this route was first US-31, US-31/US-33, then just US-33, and now M-51.
  The entire route of M-51 north of Niles was formerly designated as a part of M-40 before M-40 was transferred to the former route of M-119 between Paw Paw and US-12.
  New! 2024-01 By 2018, the twin overpasses on US-12 at the M-51 interchange south of Niles along the "Niles Bypass" were 63 years old, having been built in 1955, and the interchange itself had been constructed using older specifications which no longer met current standards. With the overpasses needing replacement, MDOT kicked off a Planning & Environmental Linkages (PEL) study to consider alternatives for both the outmoded interchange as well as the entire M-51 corridor from the Indiana state line northerly to BUS M-60 near downtown Niles. Alternatives for the junction included replacing the overpasses and ramps with updated versions using somewhat more modern specifications, rebuilding the interchange as a simpler "diamond" interchange, and several at-grade alternatives including a roundabout, signalized intersection with direct left turn movements and a signalized intersection with indirect left turns (e.g. Michigan Lefts). Although the updated interchange was deemed the best alternative in terms of traffic operations (travel delay, pedestrian accommodations, motorist safety and geometry), MDOT decided in 2019 to remove the interchanges—both US-12 overpasses and connecting ramps—and replace it with an at-grade signalized intersection with Michigan Lefts as well as making similar improvements to the existing US-12 & Third St signalized intersection just to the west. Reasons for choosing the lower-scoring alternative included lower initial construction cost—up to $9 million cheaper—and lower future maintenance costs. Another reason cited by MDOT was the existing interchange being "out-of-character" with the overall US-12 bypass route... even though the US-12 & M-60 interchange sits just 1½ miles to the east. Work to remove the 1955-era US-12 & M-51 interchange began in September 2023 with a new intersection being constructed during 2024. (See US-12 over M-51 Interchange website from MDOT.)
  In "State Trunkline Needs, 1960–1980," a set of maps prepared by the State Highway Dept's Office of Planning, Programming Division in 1960 showing possible additions, upgrades and improvements to the state trunkline system over the ensuing twenty years, MSHD staff recommended many changes to the route of M-51—which, at that point, ran from Port Huron northerly through Sanilac Co, ending at M-142 between Harbor Beach and Verona—during that timeframe, including the following major change:
  • Jurisdictionally transferring the southern half of the route of M-51 to local control, beginning at M-136 northwest of Port Huron northerly to the eastern jct with M-46 in downtown Carsonville. The remainder of the route from M-46 west of Carsonville to M-142 between Harbor Beach and Verona was to remain on the state trunkline highway system. One of the assumed reasosn for the transfer was the proposed US-25 freeway that was to run from Port Huron northerly to M-46 at Port Sanilac, just a few miles east of and parallel to this portion of M-51. This proposal was implemented within a year of the issuance of the planning maps, although the nearby US-25 freeway was never built as envisioned.
  The Dept of State Highways had planned on transferring the Eleventh St alignment of US-31/US-33 (later BUS US-31, then BUS US-12, now M-51) from BUS US-12/Oak St (now BUS M-60) southerly to local control as far back as 1960 (once the proposed US-31 freeway was completed west of Niles). By the 1970s, not only had the department improved US-31/US-33 along Eleventh St and a newly-built northbound-only segment along Twelfth St immediately south of BUS US-12/Oak St (now BUS M-60), the Dept of State Highways also proposed extending the trunkline routing, designated as part of M-51, northerly in the Twelfth St corridor back to the existing route of M-51 north of Niles. The new alignment would have featured a one-way pair mirroring the Eleventh St-Twelfth St configuration south of BUS US-12/Oak St (now BUS M-60), before merging back together as a five lane street along the Twelfth St corridor to approximately Wayne St. From there, M-51 would have angled northeasterly on a new alignment before turning due northerly as it crossed Lake St east of Thirteenth St, returning to the existing M-51 north of Monroe St. While the project was never implemented, the Dept of State Highways went as far as producing a Noise Study & Analysis document (archived) in 1974.
History: 1910s – Even prior to M-51's existence in the Thumb region, the first iteration of M-51 is designated as the primary connection between Grand Rapids and M-11/West Michigan Pike at Holland on the Lakeshore.
  1913 (Oct 1) New! 2024-05 – The first two segments of highway making up the route of T.L. 51 (Trunk Line 51) connecting Holland and Grand Rapid are officially established as state trunkline route. A 4.0-mile section is established from the Holland east city limit easterly via 8th St, then northeasterly along Paw Paw Ave to W Main Ave west of downtown Zeeland, then easterly to the Zeeland west city limit is established, as is a 16.3-mile long segment starting at the Zeeland east city limit and proceeding easterly along Byron Rd for approximately 7¼ miles, then northerly via 32nd Ave into Hudsonville, northeasterly on Balsam Dr and northerly again along 28th Ave, then easterly along Port Sheldon St to Chicago Dr running along the south side of the Pere Marquette Ry tracks, which it follows through Jenison to the Ottawa/Kent Co line.
  1914 (June 27) New! 2024-05 – Another two segments of T.L. 51 are officially established as state trunkline in Kent Co. First, from the Ottawa Co line northeasterly along Chicago Dr for 0.4 mile to the Grandville west village limit approximately 600 feet west of Canal Ave. Second, a 4.1-mile segment from the Grandville east village limit at Barrett Ave, easterly along 28th St, then northeasterly along Viaduct St to a point 1,200 feet northeast of Ivanrest Ave where it crosses the Pere Marquette Ry, then further northeasterly and easterly along Chicago Dr to the Grand Rapids west city limit at Clyde Park Ave.
  1920 (Apr 15–30) New! 2024-05 – T.L. 51 is signed in the field as M-51 as all state trunkline highways in the Lower Peninsula are scheduled to be signed with route markers during the last half of April. The portions of M-51 which have not yet been officially established as state trunkline, mainly in the cities of Holland, Zeeland and Grand Rapids and the Village of Grandville—Hudsonville wouldn't be incorprated as a village for another seven years—are "marked-and-maintained" as part of the overall route for the time being.
  1920 (Dec 8) New! 2024-05 – The 1.03-mile portion of M-51 through the Village of Grandville in Kent Co is established, begining at Canal Ave on the Grandville west village limit, then northeasterly along Chicago Dr, easterly via 30th St, and northerly on Barrett Ave to 28th St on the Grandville east village limit. Interestingly, this leaves a gap of 600 feet in the officially established trunkline route along Chicago Dr between the Grandville west village limit and Canal Ave.
  1922 (Apr 26) Updated 2024-05 – A new routing for M-51 between Zeeland and Jenison in Ottawa Co is established shaving 2.3 miles from the route between those points. The 13.2-mile portion of M-51 from the Zeeland east city limit easterly along Byron Rd, northerly via 32nd Ave, Balsam Dr and 28th Ave through Hudsonville and easterly along Port Sheldon St to Chicago Dr between Hudsonville and Jenison is cancelled as a state trunkline route and turned back to local control, while a 10.0-mile new alignment from Main Ave northerly on an unbuilt highway along the Zeeland east city limit to Washington Ave, then northeasterly via Chicago Dr through Hudsonville to Port Shelton St is officially established. The new alignment is not only shorter and more direct, but it eliminates two railroad grade crossings as it runs along the south side of the Pere Marquette Ry along the entire segment.
  1925 (May 25) Updated 2024-05 – The established route of M-51 through Grandville is replaced with a shorter, more direct alignment. The 5.13-mile portion of M-51 from Canal Ave northeasterly along Chicago Dr, easterly on 30th St, northerly along Barrett Ave, easterly on 28th St, northeasterly via Viaduct St to 1,200 feet northeast of Ivanrest Ave, then further northeasterly and easterly along Chicago Dr to the Grand Rapids east city limit at Clyde Park Ave is cancelled as a state trunkline route and turned back to local control. The new 5.0-mile route re-establishes the Chicago Dr portion from Canal Ave to 30th St in Grandville and actually continues 600 feet farther to the west to eliminate the gap in the established route between the Grandville west village limit and Canal Ave, then continues northeasterly along Chicago Dr from 30th St through the remainder of Grandville and to the point 1,200 feet northeast of Ivanrest Ave, then also re-establishes Chicago Dr from there northeasterly and easterly to the Grand Rapids east city limit at Clyde Park Ave.
  1927 (May 15) Updated 2024-03 – The various state trunkline designation changes due to the debut of the U.S. Highway system in the State of Michigan become official as to the many modifications to other routes affected by those changes. M-21, which up to now was only a Grand Rapids-to-Emmett route, is extended west from east of Grand Rapids through Grand Rapids, Grandville, Hudsonville and Zeeland to Holland over the former route of M-51, thus causing the end of the first iteration of M-51. However, the second iteration begins immediately as a route in the Thumb region. From M-29 (re-designated from M-31, now present-day M-25) in Port Huron, M-51 now replaces the M-27 designation north-northwesterly through Croswell, Applegate and Deckerville, terminating at M-83 (also newly redesignated from M-31, present day M-142) five miles west of Harbor Beach.
  1931 (May 19) Updated 2024-03 – Act 131 of 1931—the Dykstra Act—is passed allowing the State Highway Dept to take over control of state highways running into and through incorporated cities, thereby officially incorporating them as state trunkline highways. The portion of M-51 affected includes the 0.8-mile segment along Pine Grove Ave in Port Huron from Church St southerly to M-29 at Stone St, and the joint M-29/M-51 portion along Pine Grove Ave and Huron Ave from Stone St southerly into downtown Port Huron to the termini of M-51 and US-25 which now are officially established as a trunkline route.
  1940 (mid) Updated 2024-05 – A new US-25A (US-25 ALTERNATE) designation is created on the north side of Port Huron, running primarily via present-day M-25 from Lakeshore Dr southerly to M-51/Pine Grove Ave, then southeasterly along with M-51 back to US-25 in Port Huron. It is presumed this new alternate route is created to allow US-25 traffic access to the newly-completed Blue Water Bridge, which passes over the route of US-25, itself running too close to the shore at that point.
  1943 (Feb 26) Updated 2024-05 – The 7.0-mile stretch of M-51 heading northerly from Carsonville in east-central Sanilac Co along Maple Grove Rd (N Main St in Carsonville), then westery via Forester Rd to Ruth Rd is cancelled as a state trunkline route and turned back to local control. In its place, M-51 is rerouted to run westerly from Carsonville along M-46/Sanilac Rd, turning northerly for four miles along Ruth Rd, which is established as a trunkline route, back to its previous route at Forester Rd, about three miles south of Deckerville. While the length of M-51 is unchanged with this realignment, it reduces overall state trunkline mileage by three miles, as M-51 now runs concurrently with M-46 for the three mile stretch west of Carsonville.
  1956 (Mar 26) Updated 2024-05 – The route of M-51 is upgraded in eastern Sanilac Co between Croswell and Applegate and included realignments to remove several curves at Aitken Rd and Townsend Rd. First, the 1.7-mile portion of existing M-51 from a point ¼ mile north of County Farm Rd northerly to Aitken Rd, westerly along Aitken Rd, then northerly again for another ¼ mile is cancelled as a state trunkline route and replaced by a new 1.2-mile alignment with sweeping, gentle curves. The ¾ mile segment of the former M-51 south of Aitken Rd and the ¼ mile portion north of Aitken Rd are actually abandoned as public roadways and the portion of Aitken Rd in between is turned back to county control. At the same time, the reverse curve at Townsend Rd one mile to the north of Aitken Rd is replaced with a much gentler curve, with the former route of M-51 being obliterated.
  1959 – The final 6 miles of gravel surface on M-51 are paved, from Applegate to Carsonville.
  1962 (June 30) Updated 2024-05 – Purportedly due to "the low volume of traffic on M-51 [that] failed to quality it as a state trunkline," the portion of M-51 from M-46 in Sanilac Co at Carsonville southerly into St Clair Co to M-136 is cancelled as a state trunkline route and turned back to county and municipal control. Specificially, the joint M-51/US-25A segment from Port Huron northwesterly to 24th Ave retains the US-25A designation, while the 4.5-mile section along Pine Grove Ave from there northwesterly, Keewadin Rd westerly and Beard Rd northerly is redesignated as an eastern continuation of M-136. The 17.9-mile section of former M-51 along North Rd from Beard Rd in St Clair Co, then westerly along Burtch Rd, and northerly via Wildcat Rd into Sanilac Co to M-90/Peck Rd east of Croswell, and the 19.5-mile segment from M-90 in Croswell northerly through Applegate to M-46 in downtown Carsonville are both cancelled as a trunkline. The three-mile concurrent M-46/M-51 segment from Carsonville westerly becomes just M-46, while the remaining 27.1 miles of M-51 from M-46 northerly to M-142 remain as-is. For now.
  1965 (Sept 7) Updated 2024-05 – The remainder of M-51, the 27.1 miles from M-46 west of Croswell northerly through Deckerville and Ruth to M-142 west of Harbor Beach, is cancelled as a state trunkline route and turned back to county and municipal control. The second iteration of M-51 now comes to a close.
  1971 (Sept 8) – The State Highway Dept announces a change in highway route designations involving M-40 and M-119 in Van Buren, Cass and Berrien Cos to go into effect later in the fall. From Paw Paw, M-119 will be supplanted in its entirety by a rerouted M-40, which will now continue south from Paw Paw through Lawton and Marcellus, terminating at US-12 west of Mottville. The former route of M-40 between I-94 west of Paw Paw southerly through Decatur and Dowagiac to Niles will be redesignated as M-51. The concurrent I-94/M-40 segment between Exits 56 and 60 becomes just I-94. Reasons given for the change by MSHD officials include motorist confusion with having M-40 routed along I-94 for four miles and the M-119 route from Paw Paw southerly being a much more logical routing for M-40 to follow.
  1971 (Nov) – Following completion of a widening project along M-40 in downtown Dowagiac, the route designation changes for M-40 and M-119 announced earlier in the year take effect. All M-119 route markers are changed out for M-40 signs, while all M-40 signs between I-94 at Exit 56 and downtown Niles are swapped out for new M-51 markers. The M-119 route designation is retired at this point and the length of M-40 is shortened by 9½ miles. The newly created M-51 now begins at I-94 Exit 56 west of Paw Paw and continues through Decatur and Dowagiac, terminating at BUS US-12/US-31/US-33/Main St in downtown Niles.
  1990 (Oct 8) – The route of M-51/M-62 through downtown Dowagiac is realigned when the portion of Division St between Main St and Front St is established as a state trunkline route, while the former route along Main St (from Division St to Front St) and Front St (from Main St to Division St) is cancelled as a state trunkline route and turned back to city control. The realignment results in a shorter and more direct route for both trunklines. The intersection of Main St & Division St is also reconfigured to favor the through trunkline route, requiring eastbound Main St traffic at Division St to make a 90° turn to continue into downtown via Main St.
  1998 (Apr 5) – On April 5th, US-33 is 'decommissioned' in Michigan and M-51 is extended southerly from downtown Niles via BUS US-12 to US-12/Pulaski Hwy (replacing the BUS US-31 designation along that segment), then southerly via the former US-33 to the Indiana state line at a connection with IN SR-933.
  2010 (Mar 5, Apr) – On March 5, the BUS US-12 route designation is "decommissioned" in the Niles area due to the transfer of four blocks of Main St in downtown Niles to city control. While the remaining western portion of BUS US-12 is supplanted by an extended M-139 designation, the eastern portion retains the M-51 designation that had been co-signed with since 1998. (See Niles Area Trunklines Map, 2010–.)
Controlled Access: No portion of M-51 exists as freeway or expressway.
NHS: One segment of M-51 is on the National Highway System (NHS), from the southern terminus at the Indiana state line northerly to the intersection of M-51/N 5th St & Lake St on the north side of Niles. (5.9 miles) (The segment from the US-12 interchange south of Niles northerly to Lake St north of downtown was added in 2012 with the passage of the MAP-21 funding and authorization bill.)
Continue on: US-33 and SR-933 into Indiana – via the Indiana Highway Ends website
Memorial Highway: At present, no portion of M-51 has been designated as part of a Memorial Highway.
  • M-51 @ Michigan Highway Ends – photos of the termini of M-51 at Dan Garnell's archived Michigan Highway Ends website.
  • Michiana Roads – part of Marc Fannin's Roadfan.com website dedicated to the area of Southwest Michigan and Northern Indiana known by many as "Michiana."
  • Niles Area Trunklines Map, 2010– – After decades of regular reroutings, transfers and changes in route designations, the Niles area can be quite confusing when it comes to its highway routings. This map displays the Niles area as it exists at present.
  • Noise Study & Analysis, M-51 City of Niles – Berrien County, Main St to Pucker St – a 1974 Dept of State Highways document with details on the proposed three-mile relocation of M-51 on the east side of Niles.
  • Historic M-51 Bridges from Nathan Holth's HistoricBridges.org website:
    • US-12 M-51 Overpasses"These bridges may be one of the few surviving examples of a divided highway passing over a roadway that retain original R4 style railings. ... This bridge is a rare look at what all of Michigan's early freeways would have looked like, all decked out in Michigan's beautiful R4 railings."
    • Updated 2024-05 Ruth Road Bridge – On the 19271965 route of M-51 in Sanilac Co: "This steel stringer bridge is noted for its unaltered R4 railing."
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