Tehuantepec Dry Canal

The Tehuantepec Dry Canal is a major interoceanic ship railroad across the Isthmus of Tehuantepec in southern Mexico. It is one of two major trade routes connecting the Atlantic and Pacific Oceans across Central America and competes with the Nicaragua Canal to handle the bulk of inter-oceanic shipping. As of 2021 it handles a narrow majority of inter-oceanic cargo.

The present Dry Canal evolved from the Tehuantepec Inter-Oceanic Railway, an inter-oceanic line which physically carried ships. The modern network consists of essentially massive-scale train ferrying of goods between the southern terminus at Salina Cruz and the northern terminus at Coatzacoalcos.

Origins
The Tehuantepec Isthmus has been eyed as a potential route across Central America since the Spanish colonial period. However, it emerged as a serious contender for an inter-oceanic linkup only in the 1870s and 1880s, with talks to build a canal across the shortest possible route - Panama - at loggerheads in the face of grievous disputes between France, the Confederate States of America and Colombia over ownership of such a canal.

As the political disputes ground onwards, the most successful alternative to emerge was a program promoted to the United States by James Buchanan Eads: The construction of a massive ship railway across the Isthmus. The railway would load then-modern liners and freighters onto a 350-foot trestle akin to a mobile drydock, which would then be pulled by a fleet of locomotives across the Tehuantepec Isthmus - a distance of 200 kilometres. The audacious scheme was initially ridiculed, but Eads' fervent lobbying - and the prospect of the breakaway Confederacy holding a stake in a Colombian canal and potentially carving out American trade for exclusion - won the plan steadily greater acceptance. The American and Mexican governments ultimately concluded an agreement in the 1880s to construct the ship railroad.

Construction of the inter-oceanic route was challenged by both thick jungle in the northern section of the isthmus and inaccurate elevation mapping in the southern, but ultimately the selected route would take the railroad through Chivela Pass, the lowest possible ridgeline it could pass through. Eads himself would not live to see the project come to fruition. American and British funds flowed into southern Mexico to cut back much of the jungle and plot out the route, with much of the ridgeline handled by extensive blasting to create a level and somewhat lowered route with greater shelter from the winds - again at immense cost. It was soon discovered that wind conditions through the pass could occasionally generate gusts sufficient to sandblast paint off the hulls of carried ships, creating a risk of knocking them off the trestle altogether; the problem was solved by heightening the sides of the trestle with robust supporting structures to keep ships fully upright.

While the construction of the portage railway was less costly in lives and men than a wet canal, nearly 8,000 workers were killed during the construction of the railway. By the time it opened in 1911, the Tehuantepec Inter-Oceanic Railway had actually outlasted competing canal plans: France's efforts in Colombia had crumbled, the Confederacy was still mired in post-Civil War debt and unable to fund so much as a cobblestone footpath, and efforts to build a canal through Nicaragua were stymied by infighting between the Centroamerican constituent powers.

Original ship railroad
The original Tehuantepec Inter-Oceanic Railway was effectively a temporary solution to the canalization problem, coming at a time when oceangoing ships were steadily growing larger. The ship could handle liners of up to 600 feet in length, but extensive upgrades would be required for the system to carry larger vessels. Nevertheless, the railway proved relatively successful in the early going, allowing for entire vessels to be hauled across the Isthmus within a couple of days.

The issue of oversized vessels was resolved in the 1930s, when a French-Centroamerican consortium concluded work on a second route, canalizing existing waterways through Lake Nicaragua. While many smaller ships continued to make use of the isthmian railroad, larger ships tended to take the Nicaraguan route. This period coincided with a general downturn in traffic through the Isthmus.

Dry Canal transition
The importance of the Tehuantepec route increased abruptly with the onset of the Cold War and the emergence of Colombia, Centroamerica and Haiti into the socialist sphere. Fears of Centroamerican closure of the Nicaragua Canal ran rampant, and covert and overt efforts commenced to try and safeguard transit through the waterway in the name of saving global trade. These culminated in the Christiansted Agreement of 1959, in which the Centroamerican government agreed to treat the Canal as an international waterway and prohibited its closure, but did not prohibit them from imposing tolls.

By this time, modern ships had vastly outgrown the Tehuantepec route, with most modern oceanic transports far too large to be carried. A Mexican proposal to upgrade the network was well-received by the United States and other Western Allies, however. The proposal envisioned transforming the railway from a portage canal to a "dry canal," effectively a massive shore-to-shore transfer system designed to rapidly offload cargo onto deck-level railways and trans-ship it to vessels at the other side. The proposal would eliminate the engineering impossibility of ferrying kilometre-long freighters through the mountains by train and substantially speed loading and offloading times.

Through the 1960s, work proceeded to upgrade the network, finally concluding in 1967, when the American freighter MV Laurentian Giant pulled up to the loading platform at Coatzacoalcos and unloaded its holds onto waiting fleets of railcars. Within a day, the cargo had been pulled across Mexico to be loaded onto a waiting second ship.

The remodeling of the ship railroad was as much an economic boon for shippers as it was an economic shot across the bow of the Three Central American Jaguars: It was an effort to divert lucrative trade away from Nicaragua, strengthening US ally Mexico and weakening Soviet ally Centroamerica in the hopes of undermining the socialist project in Latin America. The project drove substantial investment into southern Mexico, including an expansion of the corridor to add more loading docks and rail lines, nearly tripling its handling capacity. The system underwent smaller adjustments to allow a train ferry system to be utilized. Cargo ships gained the ability to carry entire lines of loaded train cars aboard, then pull up to the drydock and connect their deck rails to the network, at which point the cars could simply be released onto the tracks and pulled across.