Mackinac Bridge

Mackinac Bridge
Coordinates	45°48′58″N 84°43′37″W
Carries	4 lanes of Interstate 75
Crosses	Straits of Mackinac
Locale	Mackinaw City and St. Ignace, Michigan
Other name(s)	Mighty Mac or Big Mac
Maintained by	Mackinac Bridge Authority
Characteristics
Design	Suspension bridge
Total length	26,372 feet (8,038 m)
Width	68 feet (20.7 m)
Height	522 feet (159 m)
Longest span	3,800 feet (1,158 m)
Clearance above	200 feet (61 m)
Clearance below	155 feet (47 m)
History
Opened	November 1, 1957
Statistics
Daily traffic	11,600
Toll	$1.25 per axle for passenger vehicles ($2.50 per car). $2.00 per axle for motor homes. $3.00 per axle for commercial vehicles.
Location

The Mackinac Bridge (pronounced /ˈmækɨnɔː/, with a silent "c"), is a suspension bridge spanning the Straits of Mackinac to connect the non-contiguous Upper and Lower peninsulas of the U.S. state of Michigan. Envisioned since the 1880s, the bridge was completed only after many decades of struggles to begin construction. Designed by engineer David B. Steinman, the bridge (familiarly known as "Big Mac" and "Mighty Mac") connects the city of St. Ignace on the north end with the village of Mackinaw City on the south.

Longest between anchorages

The bridge opened on November 1, 1957, ending decades of the two peninsulas being solely linked by ferries. A year later, the bridge was formally dedicated as "the world's longest suspension bridge between anchorages". This designation was chosen because the bridge would not be the world's largest using another way of measuring suspension bridges, the length of the center span between the towers— at the time that title belonged to the Golden Gate Bridge, which has a longer center span. By saying "between anchorage", the bridge could be considered longer than the Golden Gate Bridge, and also longer than the suspended western section of the San Francisco-Oakland Bay Bridge. (That bridge has a longer total suspension but is a double bridge with an anchorage in the middle.)

The Mackinac Bridge is the longest two tower suspension bridge between anchorages (8,614 feet) (2,626 m) in the Western Hemisphere. Much longer anchorage-to-anchorage spans have been built in the Eastern Hemisphere, including the Akashi-Kaikyo Bridge in Japan (12,826 feet) (3,909 m). However, because of the long leadups to the anchorages on the Mackinac, from waterline to waterline it is much longer than the Akashi-Kaikyo (5 mile compared to 2.4 mile).

The length of the bridge's main span is 3,800 feet (1,158 m), which makes it the third-longest suspension span in the United States and tenth largest worldwide.

History

Before the construction of the bridge, the typical way to cross the Straits of Mackinac was by ferry. A fleet of nine ferries could carry up to 9,000 vehicles per day. Traffic backups sometimes stretched to Cheboygan, Michigan, 16 miles (26 kilometers) away from Mackinaw City. Year-round boat service across the straits had been abandoned as impractical because of the cold winters which would often freeze the water across the entire strait. Following the opening of the Brooklyn Bridge in 1883, local residents began to imagine such a structure could span the straits. In 1884, a store owner in St. Ignace published a newspaper advertisement that included a reprint of an artist's conception of the Brooklyn Bridge with the caption "Proposed bridge across the Straits of Mackinac."

A Mackinac Island ferry passing in front of the Mackinac Bridge.

The idea of the bridge was discussed in the Michigan Legislature as early as the 1880s. At the time the area was becoming a popular tourist destination, including the creation of Mackinac National Park on Mackinac Island in 1875.

Despite the perceived necessity for the bridge, several decades elapsed with no formal plan. In 1920, the Michigan state highway commissioner advocated the construction of a floating tunnel across the straits. At the invitation of the state legislature, C. E. Fowler of New York City put forth a plan for a long series of causeways and bridges across the straits from Cheboygan, 17 miles (27 km) southeast of Mackinaw City, to St. Ignace, using Bois Blanc, Round, and Mackinac Island as intermediate steps.

In 1923, the state legislature ordered the State Highway Department to re-establish ferry service across the strait. By 1928, however, the service had become so expensive to operate that Michigan Governor Fred Green ordered the department to study the feasiblity of building a bridge across the strait. The department deemed the idea feasible, estimating the cost at 30 million dollars.

In 1934, the Michigan Legislature created the Mackinac Straits Bridge Authority of Michigan, to study the feasiblity of the bridge, and authorized the Authority to sell bonds for the project. In the mid 1930s, the Authority twice attempted to obtain federal funds for the project but was unsuccessful, despite the endorsement of the United States Army Corps of Engineers and President Franklin D. Roosevelt. Nevertheless, between 1936 and 1940, a route was selected for the bridge and borings were made for a detailed geological study of the route.

The preliminary plans for the bridge featured a 3-lane roadway, a railroad crossing on the underdeck of the span, and a center-anchorage double-suspension bridge configuration similar to the design of the San Francisco-Oakland Bay Bridge. Since this would have required sinking an anchorage pier in the deepest area of the Straits, the practicality of this design may have been questionable. A causeway, approximately 4,000 feet (1,219 m), extending from the northern shore, was constructed with concrete road fragments from 1939-1941.

At that time, with funding for the project still uncertain, further work was put on hold because of World War II. The Authority was abolished by the state legislature in 1947 but was reauthorized three years later in 1950. In June 1950, engineers were retained for the project. Following a report by the engineers in January 1951, the state legistature authorized the sale of 85 million dollars in bonds for bridge construction on April 30, 1952. However, a weak bond market in 1953 forced a delay of over a year before the bonds could be issued.

View of the bridge looking north across the Straits of Mackinac

Engineering and construction

David B. Steinman was appointed as the design engineer in January 1953. By the end of 1953, estimates and contracts had been negotiated, and construction began on May 7, 1954. The American Bridge Division of United States Steel Corporation was awarded a contract of over 44 million dollars to build the steel superstructure. Construction took three and a half years (4 summers, no winter construction) and cost the lives of five men who worked on the bridge. It opened to traffic on schedule on November 1, 1957, and was formally dedicated on June 25, 1958. The bridge officially achieved its 100 millionth crossing exactly forty years after its dedication, on June 25, 1998. The 50th anniversary of the bridge's opening was celebrated in a ceremony hosted by the Mackinac Bridge Authority at the viewing park adjacent to the St. Ignace causeway on November 1, 2007.

The design of the Mackinac Bridge was directly influenced by the first Tacoma Narrows Bridge, which failed in 1940 because of its instability in high winds. Three years after that disaster, Steinman had published a theoretical analysis of suspension bridge stability problems which recommended that future bridge designs include deep stiffening trusses to support the bridge deck and an open-grid roadway to reduce its wind resistance. Both of these features were incorporated into the Mackinac Bridge. The stiffening truss is open to reduce wind resistance. The road deck is shaped as an airfoil to provide lift in a cross wind, while the center two lanes are open grid to allow vertical (upward) air flow, which fairly precisely cancels the lift, making the roadway stable in design in winds up to 150 m.p.h.

Facts and figures

Mackinac Bridge at night

Mackinac Bridge during a snowstorm(Picture taken from a road that leads up to the Bridge View Park).

• The Mackinac Bridge is currently a toll bridge on Interstate 75. Prior to the coming of I-75, the bridge carried US 27.
• The current toll is US$2.50 for automobiles and $3 per axle for trucks. The Mackinac Bridge Authority has proposed raising the rate to $4 for cars and $5 per axle for trucks to fund a $300 million renovation program, which would include completely replacing the bridge deck.
• Every Labor Day, two of the lanes of the bridge are closed to traffic and open to walkers for the Mackinac Bridge Walk.
• Overall length shore to shore: 26,372 feet (8,038 m) or approximately 5 miles.
• Length from cable bent pier to cable bent pier: 7,400 feet (2,256 m).
• Total width of the roadway: 54 feet (16.5 m)

Two outside lanes: 12 feet (3.7 m) wide each

Two inside lanes: 11 feet (3.4 m) wide each

Center mall: 2 feet (0.61 m)

Catwalk, curb and rail width: 3 feet (0.91 m) on each side

• Width of stiffening truss in the suspended span: 68 feet (20.7 m), making it wider than the roadway it supports.
• Height of the roadway at mid-span: approximately 200 feet (61 m) above water level.
• Vertical clearance at normal temperature:

155 feet (47 m) at the center of the main suspension span.

135 feet (41 m) at the boundaries of the 3,000 feet (914 m) wide navigation channel.

• Construction cost: $99.8 million (1957 USD)
• Height of towers above water: 552 feet (168 m)
• Max. depth of towers below water: 210 feet (64 m)
• Total length of wire in main cables: 42,000 miles (68,000 km).
• Total vehicle crossings, 2005: 4,236,491 (average 11,608 per day)
• Speed limit: 45 mph (72 km/h) for passenger cars, 20 mph (32 km/h) for heavy trucks. Heavy trucks are also required to leave 500 feet (152 m) spacing ahead.

Work and Major Accident Fatalities

File:Mackinaw Bridge storm.JPG

The Mackinac Bridge during a thunderstorm

Five workers died during the construction of the bridge.

• Twenty-eight-year old Jack Baker and Robert Koppen died in a catwalk collapse near the north tower on June 6, 1956. Koppen's body was never recovered. For both it was their first day on the job.
• Diver Frank Pepper ascended too quickly from a depth of 140 feet on September 10, 1957. Despite being rushed to a decompression chamber the forty-six-year old died from the bends.
• Twenty-six-year old James LeSarge lost his balance on October 10, 1954 and fell into a caisson. He fell forty feet and likely died of head injuries caused by impact with the criss-crossing steel beams inside the caisson.
• Albert Abbott died on October 25, 1954. The forty-year old fell four feet into the water while working on an eighteen inch wide beam. Witnesses speculate he suffered a heart attack.

All five men are memorialized on a plaque near the bridge's southern end. Contrary to folklore, no bodies are embedded in the concrete.

One worker has died since the bridge was completed.

• Daniel Doyle fell 60-70 feet from a scaffolding on August 7 1997. He survived the fall but fell victim to the 50 degree water temperature. His body was recovered the next day in 95 feet of water.

Two vehicles have fallen off the bridge.

• Thirty-one year old Leslie Anne Plouhar died in 1989 when her 1987 Yugo plunged over the 36 inch high railing. A combination of high winds and excessive speed was blamed.
• In March 1997, a 1996 Ford Bronco went over the edge. It was later determined to be a suicide by driver Richard Alan Daraban.

Trivia

• The Mackinac Bridge is one of two segments of I-75 that is tolled -- the other is Alligator Alley in Florida.
• Travelers across the Mackinac Bridge can listen to a radio broadcast that specifically tells about the history of the bridge, as well as current driving conditions. One fact mentioned on the broadcast is that the painting of the bridge takes seven years, and when painting of the bridge is complete, it begins again.
• The Mackinac Bridge Authority has a "Drivers Assistance Program" that provides drivers for those uncomfortable with driving across the Mackinac Bridge. Those interested can arrange, either by phone or with the toll collector, to have their cars driven to the other end. There is no additional fee for this service.
• The bridge is painted foliage green and ivory white, and at night bluish vapor lamps light up the roadway while maize-colored spotlights shine on the main towers. According to legend, these colors symbolize the state's two largest universities since green and white are the official colors of Michigan State University and maize and blue represent the University of Michigan. In fact, the white-and-green color scheme was inspired by a colorized black and white image showing what the bridge would look like.
• The Mackinac Bridge Walk has been held each Labor Day since 1958. Thousands of people, traditionally led by the Governor of Michigan, cross the five-mile span on foot from St. Ignace to Mackinaw City.
• Residents of the Upper Peninsula ("Yoopers") often refer to Lower Peninsula residents as "trolls" because they live "below the bridge."
• On April 24, 1959 Captain John Lappo of the United States Air Force took his RB-47E Stratojet, a reconfigured bomber, under the bridge. Lappo lost his USAF flying privileges for violating a USAF regulation barring altitudes under 500 feet except during takeoff and landing.
• The bridge and its maintenance crew were featured in an episode of the Discovery Channel TV show Dirty Jobs on August 7th, 2007. Host Mike Rowe and crew spent several days filming the episode in May 2007.

External links

• Official site
• Photos in all seasons
• Information and lots of photos. Many wallpaper sized images.
• 1958 Mackinac Bridge Dedication @ Geocities
• Mackinac Bridge 3c Commemorative Stamp
• Detroit News archives: The breathtaking Mackinac Bridge
• Length Comparison
• Mackinac Straits Bridge at Structurae
• Monitoring the Mighty Mac, Point of Beginning, 2007