2022 CabRide Bulgaria: the sub-Balkan railway Burgas - Karlovo - Sofia

The question of studying the construction of the railway line was raised in 1909 at the regular session of the National Assembly. Funds are allocated for this, and work on the study of the line from Sofia to Sliven began the same year. The Sliven - Zimnitsa section has already been completed and put into operation on May 23, 1907.
Despite the great importance of the highway, its overall construction is hampered mainly by the study of the passage of the three watersheds connecting Stara Planina and Sredna Gora - Galabets saddles between the Kamar and Zlatitsa-Pirdop valley, Koznitsa - between Zlatishko-Pirdopska and Karlov. and The Guard at Kalofer. These natural obstacles forced the research services of new railway lines to make repeated changes to the already studied routes and search for options and solutions for overcoming them for nearly 30 years (since 1909). In 1940 the final route of the line from Makotsevo to Sopot was adopted.
After the First World War the construction of the section Tulovo - Kazanlak with a length of about 15 km was completed and put into operation on November 21, 1921. Through it Kazanlak is connected with the line Gorna Oryahovitsa - Tulovo - Stara Zagora (Main railway line 4).
The construction of the rest of the Sub-Balkan Line is regulated by the Railway Expansion Act of 1923, amended in 1925. In both laws, however, the line is considered not secondary but secondary. This perception is further reflected mainly in the parameters of the sections Dabovo - Sliven and Iliyantsi - Makotsevo.

The section Dabovo - Tvarditsa (length 26.4 km) was put into operation on November 18, 1928, and Tvarditsa - Sliven (length 44.1 km) - on December 7, 1930.

At the same time, the construction of the section Iliyantsi - Makotsevo with a length of about 46 km began. It was completed and put into operation on December 6, 1931.
Curves with small radii are allowed in both sections - about 250-300 m and a maximum slope of 15 ‰. Unnecessary ascents and descents of the line on the terrain are allowed, especially when crossing the rivers, mainly in order to obtain a lower height of the bridges and to reduce the volume of excavation works. The lengths of station platforms and tracks are insufficient.

In the period 1925 - 1934 the construction of other parts of the Sub-Balkan line between Makotsevo and Kazanlak began. We work mainly with funds and conscription from the interested population. What was done during this period was insignificant, unfinished, and from 1934 to 1938 no work was done on the line at all.
In 1937-1938 new researches were made for the section Karlovo - Kalofer - Kazanlak and a new route was established. Unlike the old one, it crosses the Strazhata watershed without tunnels, is 51 m lower and is about 2100 m shorter than the old one, offering a number of other advantages.

In order to carry out the construction on the new route Karlovo - Kazanlak in the spring of 1938, two construction sections were established - in Karlovo and in Kazanlak. Simultaneously with their organization, the plans are prepared and the line is traced. For a year and a half, 990,000 m3 of earthworks and rock works, 21,300 m3 of masonry on bridges, culverts and retaining walls have been carried out.
At that time, the section in the western direction Karlovo - Sopot with a length of 5,630 km was built, which began to operate on November 20, 1939.

The construction of the section Sopot - tunnel "Koznitsa" began in the spring of 1941. Due to irregular funding, construction work is slow. Only the earthworks and facilities from Sopot station to Rosino station have been completed and part of the railway has been laid.
The final completion of the Sub-Balkan line took place after September 9, 1944. Construction began on both sides - from Makotsevo and from Sopot. On September 14, 1947 the section Sopot - Klisura was put into operation, and in 1949 - the interstation Makotsevo - Dolno Kamartsi. Simultaneously, work is underway on the most complex part of the route Dolno Kamartsi - Klisura, on which large bridges and tunnels must be built.
Until then, no preliminary basic geological studies have been carried out in Bulgaria for such facilities, and their construction is carried out mainly by hand or with the help of small and insufficient mechanization. In 1949, 923 m were dug in the Koznitsa tunnel, in 1950 the builders reached 1723 m. On June 6, 1951 the breakthrough of the longest railway tunnel in Bulgaria (5808.5 m) was completely completed. The Galabets tunnel was drilled on November 2, 1951 and finally completed on November 21, 1951. By the end of 1951 the construction works were completed and the railway in the section Dolno Kamartsi - Klisura was laid. This part of the line is built with a minimum radius of 500 m and a maximum slope of 15 ‰.
The first train passed the route on September 7, 1952, and the grand opening of the Sub-Balkan line took place on December 21, 1952.