How the Mackinac Bridge ties a state together

Every September for the past 22 years, tiny St. Ignace at the southern tip of Michigan’s Upper Peninsula has welcomed a host of big rigs for the Richard Crane Memorial Truck Show. The weekend’s highlight is the Saturday evening Parade of Lights across the Mackinac Bridge into Mackinaw City on the southern “mainland” and back to St. Ignace.

With almost 200 trucks escorted by the Michigan State Police, the Mighty Mac sparkles like a 5-mile-long set of Christmas lights, as train horns echo over the straits connecting Lake Huron and Lake Michigan. (Full disclosure: Since 2003, this author and his wife have sponsored the Parade of Lights.)

This National Historic Civil Engineering Landmark celebrates its 61st birthday in 2018. Looking at it, you wouldn’t think that it’s a senior citizen. Designed and built to withstand most any assault by nature (and man), the Mighty Mac shrugs off Michigan’s fiercest cold, ice and winds while providing a crucial lifeline connecting the divided state.

Constant maintenance, including never-ending painting, also helps the bridge hide its age and carry ever increasing numbers of vehicles. In July 2017, for example, 609,916 vehicles crossed, some 5,000 more than the previous July.

To keep pace, Mighty Mac is scheduled to have its first major repairs starting in 2024, some 70 years after construction began. Crews will remove and replace all the decking and the 1,500 horizontal cross beams in the suspended span.

They will also replace the five long “stringer” I-beams that run the length of the bridge roadway below the cross-beams. The project is expected to take three years—almost as long as it took to build the span in the 1950s.

A bridge too far?

When the Mackinac Bridge opened on Nov. 1, 1957, it answered a need that had become increasingly pressing since Michigan became a state in 1837. The deep, glacier-carved gash was a major impediment for those wanting to exploit the Upper Peninsula’s mineral and timber riches, and the growing tourist industry.

The first semi-regular ferry service opened in 1881, though “regular” meant subject to weather conditions. Some ferries even carried railroad cars, increasing the flow of goods and people. But ferries were slow, relatively expensive and unpredictable, so delays and backups were the rule.

Calls for an all-weather link increased after the Brooklyn Bridge was completed in 1883. An engineering marvel, the Brooklyn Bridge was the first steel-wire suspension bridge ever built. The achievement inspired hopes that a similar bridge could span the Straits of Mackinac.

According to the Mackinac Bridge Authority’s official history, the Lansing Republican, newspaper on February 5, 1884, reprinted a story from the Grand Traverse Herald declaring “the experiment to provide all-year service across the straits by boat had failed, and that if a great east-west route were ever to be established through Michigan a bridge or tunnel would be required.”

In 1887, tycoon Cornelius Vanderbilt, the top investor in the island’s Grand Hotel, also called for a bridge. “We now have the largest well-equipped hotel of its kind in the world for a short season business. Now what we need is a bridge across the straits.”

But even with his backing, nothing happened. In fact, things got worse with the advent of the automobile. In 1923, the state started its own ferry service, but motorists still experienced miles-long backups and hours of delay.

Crossing troubled waters

Finally, in the midst of the Great Depression, the state authorized preliminary feasibility studies for a bridge. The legislature created the Mackinac Straits Bridge Authority in 1934 to conduct the studies and explore financing options.

The MSBA concluded a two-lane highway and one-track railway bridge could be built across the Straits for around $33 million. Between 1934 and 1936, the MSBA tried twice to get a federal loan for about 70 percent of cost as a Depression-era work project. President Franklin D. Roosevelt and the Army Corps of Engineers supported the plan, but the Federal Emergency Administration of Public Works rejected it.

Nevertheless, the state kept working on plans. This included building a 4,200 foot-long, $700,000 causeway on the UP side—a step that would ultimately reduce the final cost by at least $3 million, according to “The Official Picture History of the Mackinac Bridge” by Lawrence A. Rubin (Kiwanis Club of St. Ignace, Mich., 1979).

By 1940, the MSBA had picked a route and conducted studies of the route’s geology, ice and current data, potential traffic and other key issues. They scrapped the idea of a railway bridge in favor of a double suspension bridge for motor vehicles only.

The studies, and an event in Tacoma, Wash., touched off considerable debate over the project’s feasibility. The geologic data revealed that much of the underlying rock was honeycombed with voids. Could it support the massive load of a bridge?

And if Nature’s rock was solid enough, could man’s construction withstand the fierce currents, frequent high winds and the relentless grinding of winter ice? On Nov. 7, 1940, the Tacoma Narrows suspension bridge had spectacularly collapsed when high winds set the roadbed rippling like a jump rope until it fell. It wasn’t nearly as long as the Mackinac Bridge would be.

And not least, could the bridge pay for itself? The state envisioned issuing bonds, but critics predicted there’d never be enough traffic to cover the loan.

‘A symphony in steel and stone’

World War II halted virtually all planning, though the debates continued through the 1940s. Proponents slowly won converts, and in 1950, the state formed a new Mackinac Bridge Authority. The MBA issued a favorable report in 1951, and the legislature authorized seed money to start work in earnest.

In 1953, the MBA made a crucial decision. It hired renowned bridge engineer David B. Steinman as the span’s designer. Three years after the Tacoma Narrows bridge failure, he published an influential paper on suspension bridge stability. His recommendations included using open grid roadways to reduce wind resistance and improve aerodynamic stability. He also called for stronger trusses to provide greater support.

The Mackinac Bridge would be the first real-world test of his conclusions. His design would withstand 115,000 pounds of ice pressure per lineal foot of circular pier. That’s about five times greater than the highest amount ever recorded. The bridge could also withstand winds more than 2.5 times higher than the then-record of 78 miles per hour.

It also would be flexible. The center span is designed to shift as much as 35 feet east or west in high winds, though movement is slow and gradual, according to the Bridge Authority.

In an essay, Steinman once wrote, “A bridge is a poem stretched across a river, a symphony of stone and steel.” To a dedicated bridge designer, a bridge is geometry transmuted into poetry and music.” He was about to conduct his masterpiece.

Across the straits

In 1954, MBA issued $99.8 million in bonds (1954 dollars), and construction began May 7, 1954. With late 1957 as the target opening date, time constraints dogged the project from the start. Winter weather would halt much of the work, so crews worked full speed as long as they could.

The authority hired Merritt-Chapman and Scott Corp., one of the top marine foundation builders, to construct the foundations, and the American Bridge Division of United States Steel Corp. to build the steel structures. Merritt-Chapman assembled the largest bridge marine construction fleet to that time, while U.S. Steel mills in a number of locations began fabricating components.

For the “shorewalk superintendents” who watched from the shore, much of the action in 1954 was out of sight. Crews worked to install cofferdams and caissons for the foundations. As they drove the enclosures into bedrock as much as 200 feet down, barge-mounted cranes used clamshell buckets to scoop out the overlying sediment.

Once secured, the caissons and cofferdams were filled with clean crushed stone. Next came a special kind of marine grout that flowed through the stone and hardened into concrete.

GPS didn’t exist in 1954, and surveyors couldn’t just stick a pole in the water. Instead, they set up six triangulation survey towers, three on each side of the centerline of the bridge route, as well as seven tall land-based survey towers. They relayed their measurements via walkie-talkies to ensure correction location to within one-tenth of an inch.

Work on the bases of the two towers and 27 smaller foundations continued into January 1955 before winter halted progress. The partly completed caissons and cofferdams withstood the ice and cold perfectly. Crews quickly finished them when work resumed in early spring.

The gawkers on shore soon had plenty to watch. Pre-fabricated steelwork for the tower superstructure had been pre-fabbed in Ambridge, Pa. These were shipped by rail more than 500 miles to the Straits. Cranes hoisted the sections ever-higher, while other crews began installing the horizontal steel trusses that would support the roadway.

The towers were aloft as the 1956 work season and much of the focus shifted to spinning the massive steel cables. Before they could start laying the cable, they had to build a catwalk from one end of the bridge to the other. The floor of the catwalk was simple chain-link fencing, with handrails and stability supports, all held up by thick wire ropes.

Rubin wrote that an elderly lady who had watched the catwalk process wrote the Bridge Authority asking how in the world they expected cars to climb that high, steep narrow road.

The term “spinning” is somewhat misleading. The pencil-thick wires that form the cable aren’t woven or twisted together. Instead, two suspended wheels running in opposite directions pulled several wires at a time off 16-ton spools from one anchorage to the other, where they were secured. The wires were compressed into bundles, or strands, of 340 wires each, and it took 37 strands to make each 2-foot-plus thick cable.

The crews worked late into the night to finish the cable before winter, checking alignment and adjusting as needed after dark when temperature was more consistent. Steinman was so charmed by the visual effect of their work lights that he added permanent lighting to the design.

The cables were completed in November 1956, barely ahead of winter. While that project was going on overhead, crews below had installed and partially paved truss spans reaching out from the shores. They had hoped to finally link the Upper Pennisula and Lower Michigan with steel by the end of the work season, but weather forced them to stop in December with only 325 feet to go, Rubin wrote.

Though work on the bridge structure stopped for cold weather, in St. Ignace, crews spent the winter of 1956-57 assembling parts of the suspended span. Built in 120-foot long sections, they were put together on tracks so they could be rolled onto barges waiting at the shore. The first section went up on June 5. Amazingly, the crews had placed all of the sections before the end of July.

With the Nov. 1 opening date looming, the pace intensified. Some crews were busy laying decking, including the open grid grating that startles first-time visitors and paralyzes some motorists. Overhead, workers wrapped the cables tightly with thin wire and applied a protective watertight red-lead paste. Still other teams installed lighting, finished work on the cable anchorages, and, built the administration building and toll booths on shore.

The last bit of asphalt was laid only a few days before Nov. 1, but the Mighty Mac opened on time and on budget.

The job had a remarkable safety record, though five men died during construction. Two fell some 550 feet from a catwalk, one died in a diving accident, one fell in a caisson, and one drowned after a short fall into the water. Contrary to urban legend, there are no bodies buried in the concrete piers.

Don’t be afraid

Gephyrophobia means fear of crossing bridges. Some people don’t know they have it until they confront a bridge like the Mackinac Bridge. Each year, the Mackinac Bridge Authority’s Drivers Assistance Program sends workers to chauffeur some 1,200-1,400 motorists across the span.

That includes motorcyclists and even the occasional trucker, according to a May 25, 2013, story by ABC news reporter Gillian Mohney. She reported that one trucker who comes through about once a month spends the trips under a blanket in his sleeper.

It’s easy to understand why the Mac is so daunting. The roadway soars to 200 feet above the water, and the open grate decking that improves its aerodynamic stability can spark some colorful language and pucker factor, especially on one’s first ride (as this writer discovered for himself).

If you need help on the mainland side, pull into the extra lane just past the Jamet Street entrance ramp and call 906-643-7600. From the north, ask a toll collector to make the call.

Land Line thanks the Michigan DOT Communications Office for their assistance with this article.