The Trans-Iranian Railway (Persian: راه‌آهن سراسری ایران, romanized: Râh-âhan-e Sarâsari-ye Irân) was a major railway project begun in Iran in 1927 and finished in 1938. It was built under the leadership of Iran’s ruler at that time, Reza Shah. The railway was entirely funded using money from Iran. It connects the capital city, Tehran, to Bandar Shahpur (now called Bandar-e Emam Khomeyni) on the Persian Gulf in the south and Bandar Shah (now called Bandar Torkaman) on the Caspian Sea in the north. The route passes through the cities of Ahvaz and Qom. In 1961, under the leadership of Reza Shah’s son, Mohammad Reza Pahlavi, the railway was extended from Bandar Shah to a new endpoint in Gorgan. During land reforms in 1963, as part of the "White Revolution," the Trans-Iranian Railway was expanded to connect Tehran with Mashhad, Tabriz, and Isfahan. The original 1938 route from Bandar Shahpur to Bandar Shah was named a UNESCO World Heritage Site in July 2021.

Before World War I: the Russian scheme

In 1889, 1900, and 1905, some private Russian people suggested building a railway to connect the Russian Empire with British India. However, the Russian government refused these ideas because it worried that the railway might harm Russia’s control over trade in Iran and worsen relations with Britain. In 1889, Russia and Naser al-Din Shah Qajar of Iran agreed that no railways could be built in Iran without Russia’s permission. But by 1910, this agreement was canceled during the Iranian Constitutional Revolution. Iran became more worried about Russia’s influence, saw anti-Russian groups grow, and faced a new threat from Germany. To protect its trade interests, Iran decided to build a railway.

To fund the railway, raising enough money was a big challenge. The Russo-Japanese War in 1905 made it hard for Russia to get money, so it could not help pay for the project. Britain was also asked for help, but it could not agree, which delayed the railway’s start. Nikolay Khomyakov, leader of the Russian parliament, and I.A. Zveginstov, supporters of better relations between Russia and Britain, promoted a plan for a railway linking India and Europe. This was meant to stop Germany’s growing influence in the region. Germany had control over the Berlin–Baghdad railway, which connected Germany to the Ottoman Empire (modern-day Turkey, Syria, and Iraq), and planned to extend it to Tehran. Despite Russian government officials opposing the idea, some supported it.

By December 1910, a group called the Trans-Iranian Railway Consortium was formed, made up of twelve Russian banks. In 1911, nine of these banks worked with major French banks, which provided the money needed for the railway. However, the British were needed to officially start the project. The British wanted to help Iran’s economy but did not want to join the consortium through a proposed loan of four to six million pounds. Sergey Sazonov, Russia’s foreign minister, pushed for the loan, saying it would help Iran avoid bankruptcy. Lord Curzon, Britain’s leader in India, refused the loan, fearing Russia wanted to take control of India. Sazonov strongly disagreed with this accusation. Finally, in 1912, Russian, French, and British investors formed a group called Société d'Etudes to study the railway project.

In 1916, Arthur von Gwinner, head of Deutsche Bank and the Baghdad Railway, announced plans to build a part of the railway from Baghdad to Khanaqin. This made Russia rush to get British support and French funding for the Société d'Etudes. Russia focused on building the northern part of the railway from Astara to Tehran, while Britain cared more about the southern part, which it already controlled near the Persian Gulf.

At the same time, the Balkan Wars in the Ottoman Empire (1912–13) caused political instability, delaying the railway project. Investors in the Société d'Etudes hesitated because Iran’s economy was weak. Sazonov suggested appointing a strong leader in Iran to help the project. Javad Sa'd al-Dowleh, a former Iranian leader, agreed to work with Russia and Britain to use money from the Société d'Etudes to build the railway without needing approval from Iran’s new government. However, Sir Edward Grey, Britain’s foreign minister, refused to force Iran to choose Sa'd al-Dowleh as leader, fearing it would anger Iran’s new government.

The Balkan Wars made Russia and Britain realize a war with Germany and its allies might soon happen, showing the need for better cooperation between them. Sazonov grew frustrated with Britain’s refusal to support a railway route that included India and threatened to build the northern route alone. Fearing the coming war, Grey finally agreed to support the railway under the Balmoral conditions. By this time, Britain had strengthened its control over the Persian Gulf.

By June 1914, surveys for the Enzeli-Tehran section of the railway began, and by 1915, plans for the Astara-Tehran part were completed. However, progress was slow. Soon after World War I started, Russia stopped its promise to build the Tehran-Khanaqin line as agreed in the Potsdam Agreement.

After World War I

After the major disruption of World War I, Reza Shah Pahlavi started a project to build a standard-gauge railway across Iran. This railway had a track width of 1,435 mm (4 feet 8 and a half inches). The project was part of many reforms that helped Iran modernize during the time between the world wars. Even though Iran was technically independent, it was financially weak and struggled after the war. However, during the 1930s, Iran saw economic growth, more industries, higher exports, and increased agricultural production.

British and Russian officials believed railways were the best way to solve Iran’s transportation challenges. Iran’s population was spread out, and the country had few rivers, high mountains, and difficult desert areas. Some Americans and British people disagreed with the Trans-Iranian Railway, suggesting cheaper transportation methods like the U.S. Army’s Motor Transport Service. This service moved about a quarter of the goods the railway transported to the Soviet border. Some British critics, like General Percy Sykes, opposed the railway because it ran north to south instead of west to east. A west-to-east route would have allowed the British to reach their military bases in India and Mesopotamia directly and avoid giving Russia or other countries economic advantages.

Some Iranians also opposed the railway, arguing that money should be spent on building roads instead. However, if a government official criticized the heavy taxes the railway required, they could be arrested and accused of working with Britain to keep Iran underdeveloped for their own benefit.

Although the railway was expected to lower transportation costs, it actually had little effect on reducing prices. The railway was very expensive, costing Iran 2,195,180,700 rials by 1938–1939. Most of the money came from taxes on goods like sugar and tea, which were produced in factories set up as part of Reza Shah’s reforms.

In 1924, an American company called Ulen made an agreement with Reza Khan (later Reza Shah) to study the feasibility of building a railway line between Khorramshahr and the Caspian Sea. After becoming Shah in 1925, Reza passed laws to fund the railway using taxes on goods like sugar, avoiding new foreign debts that had caused problems before World War I.

To plan the railway, two test lines were built at the northern and southern ends of the proposed route. The United States formed a partnership with German companies to address competition from other countries. Starting in 1927, an international group called "Syndicat du Chemin du Fer en Perse" (including the American Ulen and German companies) began constructing the test lines. The Americans built a section from Bandar Shahpur through Ahvaz to Dezful. The Germans built a line from Bandar Shah on the Caspian Sea to the foothills of the Alborz Mountains near Shahi (Qaem Shahr). The Americans left the project in 1930 due to delayed payments from the government.

In 1933, Iran signed a contract with the Danish company Kampsax. Kampsax had experience building railways in Turkey, and the Shah chose them because they were from a small country, reducing political risks for Iran’s independence. Kampsax divided the project into 43 parts, subcontracting work to companies in Europe, the U.S., and Iran. Engineers from Kampsax supervised each part, with coordination from Tehran. The contract required Kampsax to finish the railway by May 1939. They completed the project under budget and ahead of schedule, with the railway officially opening on August 26, 1938.

The first Iranian person to operate a train on the line was named Hossein Orang. The railway passed through difficult mountainous regions, with some sections having steep slopes of up to 1 in 36. Engineers used techniques like railway spirals to navigate these areas. One famous spiral, called the Three Golden Lines (Se Khat Tala), is located in the Mazandaran branch near the Veresk Bridge. This section allows trains to ascend or descend quickly by looping through the same area at different heights. The railway has 1,394 km of track, 230 tunnels, and 4,100 bridges. Its highest point is in Arak at 2,220 meters above sea level. However, Kampsax used lighter rails (67 to 75 lbs per yard), which limited the weight of trains that could travel on the line.

During construction, several geological challenges were faced, leading to changes in the railway’s route:
– A tunnel through a salt dome was abandoned because water erosion would destroy the salt.
– A tunnel through solid rock was stopped after encountering soft gypsum that filled the excavation quickly.
– A tunnel through pumice could not be blasted or dug because tools got stuck.
– A tunnel encountered a large underground cavern, requiring a bridge inside the tunnel.
– Poor water supplies made it hard to mix durable concrete and mortar.
– Large bridges, like the Veresk Bridge, were needed to cross the Alborz Mountains.

In 1936, Beyer, Peacock & Company provided Iran with four Garratt 4-8-2+2-8-4 locomotives (works numbers 6787–6890). These became class 86.01 in 1938. Until the Anglo-Soviet invasion of Iran in 1941, these were the only standard-gauge British locomotives in Iran.

German companies supplied 65 steam locomotives for the railway’s opening in 1938. These included:
– 49 2-8-0 Consolidations: 24 from Krupp (class 41.11), 16 from Henschel & Son (class 41.35), and 9 from Maschinenfabrik Esslingen (class 41.51).
– 16 Henschel 2-10-0 Decapods (class 51.01).

The Trans-Iranian Railway also acquired 10 locomotives used by Kampsax during construction. These were Gölsdorf two-cylinder compound 0-10-0 freight locomotives, originally built for Austrian State Railways between 1909 and 1915. When Iran introduced a new numbering system in 1938, these locomotives retained their original Austrian numbers.

World War II

During World War II, the British and Russians claimed they invaded Iran because the Iranian government did not remove Germans from the country. These Germans were believed to plan a takeover of power. However, another key reason for the invasion was the important location of the Trans-Iranian Railway, which was part of a route called the "Persian Corridor." This route was vital for moving supplies and oil. Despite efforts by Iran's leader, Reza Shah, to stay neutral, the Allies decided to remove him from power. They placed his son on the throne instead, allowing them to use the railway to transport oil to Britain and supplies to the Soviet Union.

In August 1941, British, British Indian, and Soviet forces invaded Iran to protect oil supplies and secure the Persian Corridor, which connected the Persian Gulf to Soviet territories in Central Asia. In September 1941, the Allies took control of the Trans-Iranian Railway. British engineers operated the Southern Division, which ran from Tehran to Bandar Shahpur on the Persian Gulf. Soviet forces operated the Northern Division, which ran from Tehran to Bandar Shah on the Caspian Sea.

To improve railway operations, British engineers built new railway yards at Bandar Shahpur, Ahvaz, and Andimeshk. They also created a junction at Ahvaz for a new line to Khorramshahr. To increase locomotive numbers, engineers built a yard at Abadan to transfer locomotives from ships to barges, which transported them up the Karun River. A crane on the Karun River at Ahvaz helped move locomotives onto the railway. When the British first took control of the Southern Division in 1941, the railway could move only one freight train per day. By the first quarter of 1942, it transported 978 tons of freight daily. By September 1943, this number increased to 5,400 tons per day due to new locomotives, wagons, and skilled workers.

At the Ahvaz locomotive depot, the Southern Division had two German 2-10-0 locomotives, seven German 2-8-0s, and other locomotives from Austria and Britain. Most of these were in poor condition. In December 1941, British engineers began sending LMS 2-8-0 steam locomotives and freight wagons to Iran. By February 1942, 27 of these locomotives were in service. Some German locomotives were later used on the Northern Division operated by the Soviets. Between February and August 1942, 96 oil-burning LMS 2-8-0s and 19 coal-burning locomotives were added to the Southern Division. In 1942, 24 diesel-powered switchers were also delivered for use in Iran.

In December 1942, the US Army Transportation Corps (USATC) took over the Southern Division from British forces. The railway had 144 tunnels, where smoke and oil fumes made working conditions difficult for steam locomotives. Limited water supplies and the hot climate in southern Iran also challenged steam operations. The USATC decided diesel-electric locomotives were better suited for the route. They converted 13 ALCO RS-1 locomotives into ALCO RSD-1s and ordered 44 more for use in Iran. These 57 locomotives were initially used on the southern part of the Southern Division between Bandar Shahpur and Andimeshk.

For traffic between Andimeshk and Tehran, the USATC introduced 91 S200 Class steam locomotives and added 3,000 freight cars. In April 1943, 18 more ALCO RSD-1s arrived, allowing the USATC to return some British locomotives to the British Middle East Command and expand diesel operations northward. By September 1943, diesel trains reached Qom, and by May 1944, they regularly served Tehran. Freight traffic increased to an average of 6,489 tons per day in 1944.

In May 1945, transportation to the Soviet Union ended. In June 1945, the USATC removed its RSD-1 locomotives and handed control back to British authorities. Soon after, the British returned the railway to the Iranian State Railways, which later became the Islamic Republic of Iran Railways.

After World War II

The railway was extended from Bandar Shah to Gorgan in 1961.

In 2014, the Kazakhstan-Turkmenistan-Iran railway link, which is part of the International North–South Transport Corridor, was completed and began operating. This link connects Kazakhstan and Turkmenistan with Iran. A new railway line was also built to connect Gorgan to Etrek in Turkmenistan. Railways in countries that were once part of the Soviet Union use a track width of 1,520 mm (4 ft 11 + 27⁄32 in), known as the Russian gauge. This requires Iranian Railways to provide special services at the border with Turkmenistan to help trains switch between different track widths.