MacGregor Street Bridge (Jasper County, Missouri)
Built ca. 1950
Wooden bridge over the MNA Railroad on MacGregor Street in Carthage
Open to traffic

Macoupin Bridge (Macoupin County, Illinois)
Pony truss bridge over Macoupin Creek on Lake Catatoga Road south of Macoupin
Open to one-lane traffic

Madison Bridge (Greenwood County, Kansas)
Built 1926 by the Yancy Construction Co.
Open-spandrel arch bridge over Verdigris River on Old K-99 just north of Madison
Open to traffic

Madison Bridge (St. Francis County, Arkansas)
Built 1933 by the Wisconsin Bridge & Iron Co. of Milwaukee
Through truss bridge with center swing span over St. Francis River on US 70 near Madison
Open to traffic

Madison-Milton Bridge (Jefferson County, Indiana)
Built 1928-29; rehabilitated 1997
Cantilevered through truss bridge over Ohio River on US 421 between Madison, IN, and Milton, KY
Open to traffic

Maeystown Bridge (Monroe County, Illinois)
Built 1881; rehabilitated 1938
Stone arch bridge over Maeystown Creek on Mill Street at Maeystown
Open to one-lane traffic

Magill Hollow Bridge (Butler County, Missouri)
Small stone arch bridge over an unnamed creek just west of Hendrickson
Open to traffic on an unmarked county road

Main Ditch Old US 60 Bridge (Stoddard County, Missouri)
Built 1922, rehabilitated 1932
Pony truss bridge over a tributary of Main Ditch on MO 114 (Old US 60) east of Dexter
Open to one-lane traffic

Main Street Bridge (Allen County, Indiana)
Built 1921; rehabilitated 1997
Three-span arch bridge over St. Marys River on Main Street in Fort Wayne
Open to traffic

Main Street Bridge (Rock County, Minnesota)
Built 1931
Bridge over Rock River on Csah 4
Open to traffic

Main Street Bridge (Duval County, Florida)
Built 1941
Vertical lift bridge over St. Johns River on US 1 (Main Street) in Jacksonville
Open to four-lane traffic

Main Street Railroad Bridge (Ste. Genevieve County, Missouri)
Built 1901
Pony plate girder and wood trestle bridge over S. Main Street and South Fork Gabouri Creek in Ste. Genevieve
Open to railroad traffic

Manitowoc River 10th Street Bridge (Manitowoc County, Wisconsin)
Built 1987
Bascule bridge over Manitowoc River on 10th Street (Eastbound US 10) in Manitowoc
Open to traffic

Manitowoc River 8th Street Bridge (Manitowoc County, Wisconsin)
Built in 1995, replaced a bascule bridge built by Manitowoc Shipbuilding in 1926
Bridge over Manitowoc River on 8th Street (Westbound US 10)
Open to traffic

Mansfield Covered Bridge (Parke County, Indiana)
Built 1867 by J.J. Daniels; rehabilitated 1990
Covered bridge over Big Raccoon Creek on CR 620 South
Open to traffic

Maple Street Bridge (Washington County, Arkansas)
Built 1936 by Fred Luttjohann of Topeka, Kansas
Open-spandrel arch bridge over the railroad on Maple Street in Fayetteville
Open to traffic

Mapleton RR Bridge (Waukesha County, Wisconsin)
Built 1911
Bridge over Cth P on UPRR (Formerly C&NW) in Town of Oconomowoc (Mapleton)
Open to traffic

Marais des Cygnes River Bridge (Franklin County, Kansas)
Parker through truss bridge over Marais des Cygnes River on Burlington Northern Santa Fe Railroad
Open to traffic

Marais des Cygnes River Bridge (Osage County, Kansas)
Pratt through truss bridge over Marais des Cygnes River on Burlington Northern Santa Fe Railroad
Open to traffic

Marais Ditch Route B Bridge (Bates County, Missouri)
Built 1934; rehabilitated 1952
Pony truss bridge over Marais des Cygnes River Drainage Ditch on Route B
Open to traffic

Marais River Route B Bridge (Bates County, Missouri)
Built 1934
Pony truss bridge over Marais des Cygnes River on Route B
Open to traffic

Marias Des Cygnes River Bridge (Miami County, Kansas)
Built ca. 1920
Through truss bridge over Marias Des Cygnes River on 347th Street, 1.3 mi. east of Osawatomie
Open to traffic

Maries River CR 608 Bridge (Osage County, Missouri)
Built ca. 1915
Twin through truss bridge over Maries River on CR 608 northeast of Westphalia
Open to traffic with a 7 ton weight limit

Marion Memorial Bridge (Marion County, Tennessee)
Built 1929; tolls removed 1947; rehabilitated 1966
Through truss bridge over Nickajack Lake (Tennessee River) on US 41/US 64/US 72/TN 2 (Dixie Highway)
Open to two-lane traffic

Mark Road Bridge (Fayette County, Ohio)
Built 1883 by the Wrought Iron Bridge Co.; reconstructed 2007
Through truss bridge over Sugar Creek on Mark Road
Open to traffic

Market Street Bridge (Jefferson County, Ohio)
Built 1904; rehabilitated 1981
Suspension bridge over the Ohio River on WV 2 Spur (Market Street) in Steubenville
Open to traffic

Market Street Bridge (Van Wert County, Ohio)
Built 1934
Closed-spandrel arch bridge over Town Creek on Market Street in Van Wert
Open to traffic

Marsh Arch Bridge (Kossuth County, Iowa)
Built 1916 by the Marsh Engineering Co.
Pony arch bridge over East Fork Des Moines River on CR P14
Open to traffic

Marshall Covered Bridge (Parke County, Indiana)
Built 1917 by J.A. Britton
Covered bridge over Rush Creek on CR W800N
Open to traffic

Marshall Road Bridge (Orleans County, New York)
Built 1909
Through truss bridge over Erie Canal on Marshall Road, west of Medina
Open to traffic

Martha Washington Bridge (Milwaukee County, Wisconsin)
Built 1964
Concrete arch bridge over Martha Washington Drive on W. Washington Blvd. in Wauwatosa
Open to traffic

Martigney Creek Bridge (St. Louis County, Missouri)
Stone arch bridge over Martigney Creek on the Union Pacific Railroad, just beyond Robert Koch Hospital Drive
Open to railroad traffic

Martin Bridge (Lake County, Colorado)
Pony truss on a bike trail east of Leadville crossing CR 3
Open to two-lane bike traffic above and road traffic below

Martin Luther King Bridge (St. Louis, Missouri)
Built 1951; rehabilitated 1987
Cantilevered through truss over the Mississippi River in downtown St. Louis
Open to four-lane traffic

Martintown Road Bridge (Union County, Mississippi)
Built 1968
Pony truss bridge over Tallahatchie River on CR 86 (Martintown Road) in New Albany
Open to traffic

Maryland Street Bridge (Pike County, Missouri)
Built ca. 1920
Pony truss bridge over Town Branch on Maryland Street in Louisiana
Open to one-lane traffic with an 8 ton weight limit

Marys River Railroad Bridge (Randolph County, Illinois)
Through truss bridge over Marys River on the Union Pacific Railroad, south of Chester and just west of IL 3
Open to railroad traffic

Massac Creek Bridge (Massac County, Illinois)
Wooden bridge over Massac Creek within Fort Massac State Park in Metropolis
Open to one-lane traffic

McAlister Covered Bridge (Parke County, Indiana)
Built 1914 by J.A. Britton; rehabilitated 1977
Covered bridge over Little Raccoon Creek on CR E400S
Open to traffic

McClugage Bridge (Peoria County, Illinois)
Eastbound bridge built 1948; westbound bridge built 1982
Pair of cantilevered through truss bridges over the Illinois River on US 24/US 150 in Peoria
Open to four lanes of traffic

McColly Covered Bridge (Logan County, Ohio)
Built 1876 by the Anderson Green Co.; rehabilitated 2000
Three-span covered bridge over Great Miami River on CR 13
Open to traffic

McConnell's Mill Covered Bridge (Lawrence County, Pennsylvania)
Built 1874; rehabilitated 1957 and 1998
Covered bridge over Slippery Rock Creek in McConnells Mill State Park
Open to traffic

McCutcheon Road Bridge (St. Louis County, Missouri)
Built 1944
Concrete bridge over I-64/US 40 on McCutcheon Road in Ladue
Open to traffic above, but scheduled for demolition

McKenzie Creek Iron Bridge (Wayne County, Missouri)
Warren pony truss bridge over McKenzie Creek on Missouri Pacific Railroad
Open to traffic

McKenzie Creek MO 49 Bridge (Wayne County, Missouri)
Built 1929
Pony truss bridge over McKenzie Creek on MO 49 south of Gads Hill
Open to traffic

McKinley Bridge (St. Louis, Missouri)
Dedicated Nov. 10, 1910; closed to traffic in Oct. 2001; reopened 2007
Three-span through truss bridge over the Mississippi River between St. Louis and Venice, Illinois
Open to traffic

McKinley Drive Bridge (St. Louis, Missouri)
Built 1997
Replica stone arch bridge on McKinley Drive in Forest Park
Open to traffic

McKinney Bayou Old US 67 Bridge (Miller County, Arkansas)
Built 1929 by contractor McGuire & Cavender. Made obsolete 1954 by a new parallel alignment of US 67.
Concrete bridge over McKinney Bayou on CR 138 (Old US 67) northeast of Texarkana in Texarkana
Open to traffic on a frontage road

McKinney Creek Bridge (Polk County, Arkansas)
Built 1915
Pony truss bridge over McKinney Creek on CR 50
Open to one-lane traffic

McLean Branch MO 79 Bridge (Lincoln County, Missouri)
Built 1938
Through truss bridge over McLean Branch on MO 79 at Winfield
Open to traffic

McNeely Creek Bridge (Clark County, Arkansas)
Built 1923; rehabilitated 1990
Pony truss bridge over McNeely Creek on CR 12
Open to one-lane traffic

Mechanicsville Covered Bridge (Ashtabula County, Ohio)
Built 1867; rehabilitated 2003
Covered bridge over Grand River on Windsor-Mechanicsville Road
Open to traffic

Melcher Covered Bridge (Parke County, Indiana)
Built 1896 by J.J. Daniels; rehabilitated 1977 and 1995
Covered bridge over Leatherwood Creek on CR W20N
Open to traffic

Memphis-Arkansas Bridge (Shelby County, Tennessee)
Built 1949
Cantilevered through truss bridge over the Mississippi River on I-55 at Memphis
Open to four lanes of traffic

Mengo Bridge (Butler County, Missouri)
Built 1906 by the American Bridge Co.
Two-span through truss bridge over Black River on the Union Pacific Railroad, between Poplar Bluff and Hilliard
Still in use

Meramec River MO 21 Bridge (St. Louis County, Missouri)
Built 1940
Steel through arch bridge over the Meramec River on MO 21
Open to four lanes of traffic

Meramec River US 66 Bridge (St. Louis County, Missouri)
Built 1931
Deck truss bridge over Meramec River at Times Beach on Old US 66 in Wildwood
Open to traffic on a frontage road within Route 66 State Park

Merchants Bridge (St. Louis, Missouri)
Completed May 1890
Three-span through truss railroad bridge over the Mississippi River between St. Louis and Venice, Illinois
Open to railroad traffic only

Meridian Bridge (Yankton County, South Dakota)
Built 1924; rehabilitated 1953
Vertical-lift through truss bridge over the Missouri River on US 81 at Yankton
Open to traffic

Meridian Bridge (Sutter County, California)
Built 1977
Swing bridge over Sacramento Riv(Meridian) on CA 20
Open to traffic

Meridian Road Bridge (Carroll County, Indiana)
Built 1908
Pony truss bridge over Deer Creek on Meridian Road
Open to traffic

Merriam Street Bridge (Hennepin County, Minnesota)
Originally built 1887 by the King Iron Bridge Co. as a four-span truss bridge on Broadway Street; one span relocated here in 1987
Relocated through truss bridge over the Mississippi River (East Channel) on Merriam Street at Nicollet Island in Minneapolis
Open to traffic

Messmer Street Bridge (Scott County, Missouri)
Concrete bridge on Messmer Street (Old US 61) over a branch of Ramsey Creek just north of Kelso
Open to traffic

Metropolis Bridge (Massac County, Illinois)
Built 1917 under the direction of engineers C. H. Cartlidge and Ralph Modjeski
Six-span through truss bridge over the Ohio River on the CN Railroad at Metropolis
Open to railroad traffic

Miami Bridge (Saline County, Missouri)
Built 1939; rehabilitated 1983
Cantilevered through truss bridge over the Missouri River on MO 41 at Miami
Open to traffic

Michigan Avenue Bridge (Cook County, Illinois)
Built 1920
Bascule bridge over Main Branch Chicago River on Michigan Avenue in Chicago
Open to traffic

Middle Beaver Creek Lincoln Highway Bridge (Greene County, Iowa)
Built 1915
Stringer bridge over Middle Beaver Creek on 210th Avenue, Original Lincoln Highway
Open to traffic

Middle Creek Bridge (Miami County, Kansas)
Built 1907
Through truss bridge over Middle Creek on 379th Street, 1.5 mi. south and 1.8 mi. west of New Lancaster
Open to traffic

Middle Creek Bridge (Miami County, Kansas)
Pony truss bridge over Middle Creek, 1.3 mi. south and 1.0 mi. west of Beagle
Open to traffic

Middle Creek Bridge (Miami County, Kansas)
Built 1914 by the Topeka Bridge & Iron Co.
Concrete arch bridge over Jake's Branch of Middle Creek on 335th Street, 7.0 mi. south and 2.1 mi. west of Louisburg
Open to traffic

Middle Creek Bridge (Miami County, Kansas)
Built ca. 1920
Concrete arch bridge over Middle Creek, 9.0 mi. south and 3.6 mi. west of Louisburg
Open to traffic

Middle Fork 500W Bridge (Carroll County, Indiana)
Built 1916
Two-span concrete arch bridge over Middle Fork Wildcat Creek on CR 500 West
Open to traffic

Middle Fork AR 7 Bridge (Garland County, Arkansas)
Built 1933 by the Ault-Rich Construction Co. of Cassville, Missouri
Two-span open-spandrel arch bridge over Middle Fork Saline River on AR 7
Open to two-lane traffic

Middle River Bridge (Madison County, Iowa)
Built 1932
Through truss bridge over Middle River on a local road
Open to traffic

Middle River Route 774 Bridge (Augusta County, Virginia)
Built 1903
Through truss bridge over Middle River on Route 774
Open to one-lane traffic

Middle River Route 775 Bridge (Augusta County, Virginia)
Built 1908
Through truss bridge over Middle River on Route 775
Open to traffic

Middle River Route 778 Bridge (Augusta County, Virginia)
Built 1915 by the Champion Bridge Co.
Through truss bridge over Middle River on Route 778
Open to traffic

Middle Road Covered Bridge (Ashtabula County, Ohio)
Built 1868; rehabilitated 1984
Covered bridge over Conneaut Creek on Middle Road in Conneaut
Open to traffic

Middlebury Street Bridge (Elkhart County, Indiana)
Built 1931 by Bontrager Construction Co.; rehabilitated 1985
Three-span concrete arch bridge over Elkhart River on Middlebury Street in Elkhart
Open to traffic

Midland Fredericktown Road Bridge (Columbiana County, Ohio)
Built 1900; rehabilitated 2004
Through truss bridge over North Fork Little Beaver Creek on Midland Fredericktown Road (TR 1038) in Calcutta
Open to traffic

Midland Tunnel No. 1 (Chaffee County, Colorado)
Built 1887 by the Colorado Midland Railroad
First of four tunnels on CR 371 north of Buena Vista
Open to one-lane traffic

Midland Tunnel No. 2 (Chaffee County, Colorado)
Built 1887 by the Colorado Midland Railroad
Second of four tunnels on CR 371 north of Buena Vista
Open to one-lane traffic

Midland Tunnel No. 3 (Chaffee County, Colorado)
Built 1887 by the Colorado Midland Railroad
Third of four tunnels on CR 371 north of Buena Vista
Open to one-lane traffic

Midland Tunnel No. 4 (Chaffee County, Colorado)
Built 1887 by the Colorado Midland Railroad
Fourth of four tunnels on CR 371 north of Buena Vista
Open to one-lane traffic

Mill Creek Bridge (Wabaunsee County, Kansas)
Built ca. 1935
Through truss bridge over Mill Creek on Willard Road, 1.0 mi. east and 0.2 mi. north of Maple Hill
Open to traffic

Mill Creek Bridge (Wabaunsee County, Kansas)
Deck plate girder bridge over Mill Creek on Southern Pacific Railroad
Open to traffic

Mill Creek Bridge (Crawford County, Indiana)
Built 1885; rehabilitated 2000
Through truss bridge over Mill Creek on CR 220 East
Open to traffic

Mill Creek Bridge (Bourbon County, Kansas)
Built 1927
Through arch bridge over Mill Creek on North Crawford in Fort Scott
Open to traffic

Mill Creek Covered Bridge (Parke County, Indiana)
Built 1907 by D.M. Brown
Covered bridge over Mill Creek on CR N550W
Open to traffic

Mill Creek Park Suspension Bridge (Mahoning County, Ohio)
Built 1895 by the Youngstown Bridge Co.
Suspension bridge over Mill Creek in Mill Creek Park at Youngstown
Open to traffic

Mill Creek Swinging Bridge (Miller County, Missouri)
Built by Joseph Dice; rehabilitated 1978
Swinging bridge over Mill Creek on Lake Road 42-18 (Swinging Bridges Road) near Brumley
Open to one-lane traffic

Millard Crossing Bridge (Logan County, Arkansas)
This bridge crosses Shoal Creek on north east side of Magazine mountain at the former town of Millard
Timber stringer bridge over Shoal Creek on Forest Service road #1601
Open to traffic

Miller Creek Bridge (Alexander County, Illinois)
Built 1933
Pony truss bridge over Miller Creek on Old Illinois Route 3 northeast of Thebes, 1 mi. north of Thebes
Open to two-lane traffic

Miller Creek Bridge (Independence County, Arkansas)
Built 1914
Two-span arch bridge over Miller Creek on Miller Creek Road (CR 86) in Batesville
Open to one-lane traffic

Miller Creek Stone Bridge (Wayne County, Missouri)
Built ca. 1930
Low-water bridge with stone masonry foundations on CR 417 over Miller Creek beyond the end of Route JJ
Open to traffic with a 4 ton weight limit

Millers Bridge (Butler County, Missouri)
Built 1924
Pony truss bridge over Cane Creek on Route PP (Old US 60) west of Poplar Bluff
Open to two-lane traffic

Millersville Bridge (Cape Girardeau County, Missouri)
Built 1923; rehabilitated 1975
Two-span through truss bridge over Whitewater River on MO 72 at Millersville
Open to two-lane traffic on a paved road

Million Dollar Bridge (Valdez-Cordova Census Area, Alaska)
Built 1910 on the CR&NW Railroad; closed 1938; reopened as a highway bridge in 1958; fourth span collapsed in earthquake on March 27, 1964, collapsed span repaired 2005
Four-span through truss bridge over Copper River on Copper River Highway
Open to one-lane traffic

Milltown High Street Bridge (Warren County, Pennsylvania)
Built 1937; rehabilitated 1982
Pony truss bridge over Tionesta Creek on PA 2002 (High Street) in Milltown
Open to traffic

Milwaukee River Parkway, Lincoln Park, North Branch (Milwaukee County, Wisconsin)
Built 1940
Bridge over North Branch Milwaukee River on Milwaukee River Parkway
Open to traffic