The Fixed Link

Henry Petroski. American Scientist. Volume 85, Issue 1. Jan/Feb 1997.

Few large engineering design and construction projects are undertaken without opposition or controversy. Their completion alters on a grand scale the way things are, and whether such changes are for better or worse often depends on one’s point of view. Thus, in the early part of this century, San Francisco’s plan to build a dam across the Hetch Hetchy Valley, in the Yosemite National Park region of the Sierra Nevada Mountains, was opposed by the environmentalist John Muir and the Sierra Club, which took its opposition all the way to the U.S. Supreme Court. Although the dam was built and today constitutes a vital component in the infrastructure that provides water to the city on the bay 150 miles away, opposition continues. There have been calls to demolish the O’Shaughnessy Dam, as it was named after the city engineer who was the driving force behind its construction, and restore the valley to its pristine beauty. Not all battles between technological developers and environmental conservatives reach such epic proportions, but countless examples of large bridge projects do come close.

In the context of water crossings, fixed links are permanent structures, such as bridges or tunnels, that are much less susceptible to the vagaries of the weather than are ferryboats. Thus fixed links provide more reliable means of communication across a river or between an island and the mainland. Where there are narrow and shallow waterways in heavily populated and trafficked areas, fixed links have generally developed with the economy and society, for they were relatively easy to construct within contemporaneous technological experience and economic conditions. Often, however, where large cities and other significant population centers have long been developing on different sides of wide and deep waterways, dreams of fixed links fall within technological and financial reach only after considerable development has taken place. Then they frequently conflict with the strong social and cultural milieu that has evolved, not to mention the established infrastructure of business and ferry interests, and streets and buildings that would have to be closed, demolished or displaced to make way for a fixed crossing. The epic story that culminated in the Channel Tunnel between England and France spanned almost two centuries. Opposition to that fixed link had much more to do with political and environmental issues and xenophobia than with technological difficulty. British fears of invasion by armies of soldiers and rabid animals from the Continent did more to keep the tunnel from being built than anything else. In America, a bridge across the Mississippi River at St. Louis was little more than a dream of civic boosters before the strong personality of James Buchanan Eads prevailed and went forth with the design and construction of a fixed link able to resist not only the forces of the river itself but also those of ferryboat and steamboat operators, rival Chicago business interests, and a vindictive leadership in the U.S. Army Corps of Engineers. Had Eads not prevailed, St. Louis might have lost its commercial viability and become a veritable ghost town over a century ago.

Controversy Anew

Today, a world-class bridge-the longest over iceforming waters-is nearing completion across the Northumberland Strait between Prince Edward Island and the mainland of Canada, and the opposition and controversy that has surrounded this fixed link have been as fierce as any in recent history. Canada’s smallest province, this 250-kilometer-long island is nestled beside the southernmost shores of the Gulf of St. Lawrence, just off the coasts of two other maritime provinces, New Brunswick and Nova Scotia. The island is known for its crops of fine lobsters, scallops and potatoes. It is also know for being the setting of the “Anne of Green Gables” novels of the early-20th century local writer Lucy Maud Montgomery, a fact that has been turned into a significant island industry. That Anne of Green Gables, Canada’s longestrunning musical, is sponsored by the bridge development company and advertised on its userfriendly World Wide Web site is an indication of how important good public relations are believed to be for the fixed-link project.

When P.E.I., as the island is affectionately known, agreed to join the Dominion of Canada in 1873, it secured from the federal government several concessions. Although a summer-only steam ferry had run between Charlottetown, PE.I., and Pictou, Nova Scotia, as early as 1832, for becoming part of the confederation islanders gained the assurance of “efficient steam communication between the island and the mainland.” At first, this took the form of “primitive, open iceboats” that were not effective in heavy ice or storms, but in 1877 the government in Ottawa agreed to provide a subsidy for more comfortable steam service. Still more reliable year-round service came in the winter of 1918 with the introduction of ice-breaking ferries. Today, dieselpowered ferryboats provide year-round regular service across the narrowest part of the strait very near where the bridge is being built, but ferry schedules remain subject to interruption by such vagaries of the weather as high winds.

The movable links with the mainland that ferries provide an island are frequently subjects of debate. Those who treasure an island culture, relishing its remoteness and isolation and even taking a kind of pleasure in the long, slow ferry ride home from more “spoiled” locations, see a boat ride as a desirable transition between the hectic and the bucolic. There are also those, on the other hand, who are in a hurry to get back and forth between home and business, who have a truckload of perishable goods to take across the water, who grow frustrated with the wait for ferries that may sail only after weather has passed or moderated, and who curse the winter and the ice it brings as well as the summer and the tourists and seasonally long ferry lines it brings. Opponents of fixed links tend not to be overly concerned with economic growth, whereas those favoring fixed links tend to see them as panaceas for ailing economies. On PE.I., the former wished to see their island stay much as they knew it; the latter saw a fixed link as an invitation to greater tourist traffic and a greater participation in the kind of economy that the mainland enjoyed.

Fixed-link proponents generally have an advantage, in that they can pursue technical and financial possibilities with little or no formal authority. They need put forth a proposal only when they have a feasible one that they believe has a chance of winning whatever government or popular support is necessary for its implementation. It is often only then that opponents to a fixed link can react, put forth their objections and rally against the link. Depending on the inclinations of those in political office at the time, proponents or opponents will have an edge.

Solace to an Ailing Economy

Although a fixed link in the form of a tunnel under the Northumberland Strait was proposed as early as 1885, the most serious initiatives seem to have surfaced in the second half of the 20th century, when the PE.I. economy was ailing. The island population, which stood at about 110,000, was experiencing unemployment rates considerably above the national average, and other economic indicators were equally worrisome. To address the problem, the government proposed a series of reforms, which included a fuller exploitation of agricultural resources and the development of tourism as an industry.

The use of ferries to get produce and tourists from and to the island was believed to be an impediment to economic growth, and so in the mid1960s the decade-old idea of a fixed link in the form of a causeway over the relatively shallow strait again came under serious consideration. By the end of the decade, however, any kind of fixed link was rejected by the federal government in favor of an economic-development agreement and improved ferry service. (A causeway is formed essentially by dumping earth and rock in the water to form a high and dry narrow strip of land on which a road can be constructed. Such a fixed-link option across the Northumberland Strait could not maintain support as experience accumulated on the effects of the massive Canso Causeway in Nova Scotia on nearby benthic fisheries. Between 1955 and 1975, lobster catches in Chedabucto Bay declined by 95 percent, and it has been estimated that the resultant loss to the provincial economy was as much as $100 million.)

In the mid-1980s, with a progressive conservative government in Ottawa, there “appeared from nowhere” three “unsolicited private-sector proposals,” including both bridge and tunnel schemes, for a fixed link between PE.I. and New Brunswick. Not unexpectedly, considerable public debate resulted, but when islanders voted in a plebiscite in January 1988, 60 percent of them endorsed going ahead with a fixed link. Opponents of a bridge later claimed that those voting for the link understood that a tunnel was being considered as a viable option. In the meantime, consultants had been commissioned to study the economic, structural and financial viability of a fixed link, construction companies had been qualified to submit proposals, and public consultation had been initiated to consider the environmental and socioeconomic implications of likely schemes for a fixed link. By mid-1988, seven formal proposals were received by the Department of Public Works, including one for a tunnel. To the disappointment and anger of bridge opponents, only bridge proposals were finally accepted as meeting the necessary criteria.

A federal environmental assessment panel was appointed in 1989 to study the concept of a bridge across the Northumberland Strait. After extensive public hearings, the panel rejected a bridge as a fixed-link solution and suggested that a tunnel or improved ferry service be considered instead. Within three months, the Department of Public Works overruled the environmental review, however, arguing that its objections to a bridge could be overcome. A private rereview was then commissioned, and the Minister of Public Works finally determined that a bridge should pose no unacceptable environmental risks and called again for the finalist proposals to be evaluated against environmental requirements and financial criteria.

Environment and Investment

Among the issues of most concern to environmentalists and fishermen alike was that of ice-out, as the breaking up and floating away of winter ice in the strait is known. It is feared by some that delaying ice-out for more than a couple of days even once in a hundred years could alter in a significant way lobster, scallop and herring catches in the region. Early in 1992, the Minister of Public Works reaffirmed that the bridge proposals did meet environmental requirements, however, and the successful proposal was to contain the bid that incorporated a need for the lowest annual federal subsidy A low bid that amounted to $42 million in 1992 Canadian dollars for the subsidy gave the project to Strait Crossing Development Inc., a consortium of three Canadian companies. The government subsidy is a key component in the private financing of the bridge.

The project is to be completed under what is termed a design, build, finance, operate and transfer arrangement. Strait Crossing will assume all costs and financial responsibility, provided it is allowed not only to have the federal subsidy that would normally go to the ferry service but also to keep all tolls collected on the bridge for a period of 35 years, at which time the bridge would be transferred to the government as the owner, maintainer and operator. The government sees this as a good deal because it does not have to find the $840 million needed to build the bridge, no doubt at the expense of other projects, and does not have to continue to subsidize a ferry operation, including the anticipated acquisition of new capital equipment. Strait Crossing is protected against inflation and rising operating costs, but only to a degree. Opponents see the government as being taken and as eventually inheriting a 35-year-old bridge, whose 100-year design life will present uncertain maintenance and, ultimately, decommissioning costs.

Although the story of the Confederation Bridge, as it was recently dubbed, is clearly one laden with, if not dominated by, politics and economics, it is also one of the most ambitious engineering projects ever undertaken. At 11,000 meters, plus another 1,800 or so meters of approach spans, it is one of the longest water-spanning bridges in the world, not to mention the fact that it spans ice-forming water. To address the environmental issue of ice-out and to provide sufficient clearance for shipping, as well as to keep construction costs down, the bridge was designed with as few piers in the deeper water as technologically feasible and with a typical vertical clearance of 40 meters, rising as high as 60 meters above the water at the navigation channel.

The massive concrete piers of the main bridge are being fabricated in two main parts that are designed to be fitted together at their resting place in the strait. The pier bases rest in dredged recesses directly on the bedrock at the bottom of the strait. A pier shaft, which will be the visible part of the structure, slips over the top of the pier base, and the entire assembled bridge is designed so that its sheer weight will keep it in place. As protection against the forces of ice, the pier shafts have incorporated into their design ice shields in the form of conical skirts, up the exterior slope of which the ice will rise and thus be broken under its own weight. The bridge superstructure is of a cantilever design, which means that balanced atop the piers are 190meter-long precast reinforced hollow-box-section concrete spans, which are also post-tensioned-that is, fitted inside with taut cables that not only compress the concrete to obviate cracking but also assist in carrying the load. A 60-meter gap between the tapered cantilevers is filled by dropping in a 60-meter suspended span that produces a continuous and visually graceful span across the wide strait.

The construction of a bridge with such massive components takes special engineering considerations. To avoid having to erect coffer dams or employ caissons in the hostile and annually frozen waters of the strait, all pier and span components are prefabricated in a construction yard on nearby PE.I. Special crawler vehicles capable of lifting and transporting completed concrete components as heavy as 8,200 metric tons carry them to a landing where they are picked up by the heavy-lifting vessel Svanen, which takes them out into the strait and sets them precisely in their ultimate locations with the aid of a computerized satellite global-positioning system. The HLV Svanen was used originally to put heavy girders in place on the Store Baelt Bridge, which connects mainland Denmark with some of its islands and is itself a fixed-link project of historic and heroic proportions. After that project was over, the Svanen had its height increased to 100 meters and its twin 94-meter-long pontoons widened for greater stability and buoyancy Then the heavy-lift vessel was towed across the Atlantic on a submersible barge to do service in the Northumberland Strait.

The Long Drive

Construction on the new fixed link began in October 1993, with the preparation of the 60-hectare construction yard and staging facility. Since the summer of 1995, ferry passengers between Cape Tormentine, New Brunswick, and Borden, Prince Edward Island, have watched the towering Svanen ferry bridge-pier and girder components between the construction yard and their places in the strait. The bridge, which will have high and solid concrete parapets to keep acrophobic drivers from freezing at the wheel midway across, will follow a gently curving route so as to address the problem of drivers becoming hypnotized while traveling down a monotonous 13kilometer straight and narrow concrete channel.

In the summer of 1996, on the ferry ride to PE.I., itself a sinuous route from dock to dock, regular and first-time passengers alike tended to list the vessel by congregating portside so they could view the bridge in progress, with its isolated piers, its gapped cantilevers and its few completed spans. Some gazed wistfully at the stillwide and untouched stretch of water in the middle of the strait. Only as the ferry curved into the small harbor at Borden, with the construction yard off to starboard, did the scale of the bridge become evident. Pier bases and shafts, cantilever and drop-in girders, in varying stages of production, were aligned in rigid rows with the concrete tracks and rail lines along which they would be carried by the turtle-like crawling machinery to be loaded on the Svanen. The construction of the bridge was the talk of the ferry and the island, and guided tours of the construction yard were popular with residents and tourists alike.

The bridge is scheduled to be completed and operational by May 31,1997, at which time Strait Crossing will begin collecting its subsidy and tolls. Tourism is hoped to increase by as much as 25 percent in response to its completion, and the island economy is expected to be revitalized. Opponents are not as optimistic, however, and they point to the hundreds of jobs that will be lost by the closing of ferry service. They also remain fearful of what will happen to the area fishing industry. The strait ice broke up nicely during the winter of 1996, the first year any piers were in place, but the installed piers were then still few and the winter was unusually mild. How the bridge will affect the ice and the environment generally in the long term remains to be seen, say those who still would have preferred a tunnel or no fixed link at all to P.E.I.