Case Studies: the St Lawrence Seaway, TAZARA and the Trans-African Highway

1Three routes, three purposes

Each of these three routes was built to solve a geographical problem. The St Lawrence Seaway lifts ocean ships into the heart of North America. The TAZARA railway gave landlocked Zambia a route to the sea that avoided hostile neighbours. The Trans-African Highway aims to join Africa's capitals by road. Study each the same way: purpose, route and engineering, benefits, problems.

2Case study 1: the St Lawrence Seaway

Purpose and route. Built jointly by Canada and the USA and opened in 1959, the Seaway lets ocean ships sail from the Atlantic up the St Lawrence River into the Great Lakes. With the Welland Canal it forms the core of a waterway about 3 700 km long, from the Gulf of St Lawrence to Duluth at the western end of Lake Superior.

Engineering. Rapids on the St Lawrence and the Niagara Falls between Lakes Erie and Ontario blocked ships. The Seaway proper, from Montreal to Lake Erie, uses 15 locks: 7 on the St Lawrence and 8 on the Welland Canal, which bypasses Niagara (Figure 1). Ships are lifted about 183 m from sea level to Lake Superior, the last step through the Soo Locks. Dams built with the Seaway also produce hydroelectric power.

Figure 1: The Great Lakes–St Lawrence waterway in profile.

• Benefits. Cheap bulk transport of grain from the prairies, iron ore, coal, steel and salt; growth of lake ports and industrial cities such as Chicago, Detroit, Cleveland, Toronto and Hamilton; jobs; hydroelectricity.
• Problems. Ice closes the Seaway for about three months each winter; locks limit ships to about 225 m long and 24 m wide, too small for the largest modern container ships and bulk carriers; competition from railways, lorries and pipelines; invasive species such as zebra mussels, carried in ships' ballast water; high costs of maintaining locks and dredging channels.

3Case study 2: the TAZARA railway

Purpose. Zambia is landlocked, and its economy depended on exporting copper. After Rhodesia (now Zimbabwe) declared independence under a white-minority government in 1965, Zambia's routes south and through Portuguese-ruled Mozambique and Angola became unsafe or closed. Zambia and Tanzania asked Western donors to fund a railway to Dar es Salaam; when they refused, China agreed.

Route and construction. The Tanzania–Zambia Railway (TAZARA) runs about 1 860 km from Dar es Salaam to New Kapiri Mposhi in Zambia's copper region. It was built between 1970 and 1975 with an interest-free Chinese loan and tens of thousands of Chinese, Tanzanian and Zambian workers, crossing swamps, the Great Ruaha valley and steep escarpments with many bridges and tunnels. It uses the 1 067 mm gauge of Zambia's railways.

• Benefits. A secure outlet for Zambian copper and imports; it opened up southern Tanzania for farming and settlement (Kilombero valley, Mbeya); passenger services for remote villages; a symbol of African cooperation and South–South partnership.
• Problems. Poor maintenance and shortages of locomotives and wagons; derailments and delays; financial losses; competition from lorries on the parallel TanZam Highway; and a different gauge from Tanzania's older central line, so wagons cannot run straight through. It has carried only a fraction of the 5 million tonnes a year it was designed for. In 2024 the governments of China, Tanzania and Zambia agreed a plan to rehabilitate the line.

4Case study 3: the Trans-African Highway

Purpose. Planned since the early 1970s by the UN Economic Commission for Africa, the African Development Bank and the African Union, the Trans-African Highway is a network of nine routes, about 56 700 km in total, intended to join Africa's capitals and boost trade between African countries.

• Benefits. Regional trade, as encouraged by the African Continental Free Trade Area; links for landlocked countries; tourism; access for remote regions; political unity.
• Problems. Many missing or unpaved links, especially through the forests and conflict zones of Central Africa; different road standards, axle-load limits and rules in each country; slow border crossings; insecurity; high building and maintenance costs; heavy rains that wash out earth roads. Some sections, such as much of the Trans-Sahara route and the road from Nairobi to Addis Ababa, have been paved; others remain tracks.