Tünel, the 2nd underground railway in the world

The Tünel (English: Tunnel ) is a short underground railway line in Istanbul, Turkey. It is an underground funicular with two stations, connecting the quarters of Karaköy and Beyoğlu. Located at the northern shore of the Golden Horn, the underground railway tunnel goes uphill from close to sea level and is about 573 metres long.[1] Inaugurated on January 17, 1875, the Tünel is the second-oldest subterranean urban rail line in the World after the London Underground (1863), and the first subterranean urban rail line in continental Europe; though the first full subway line with multiple underground stations in continental Europe was Line 1 of the Budapest Metro (1896)

 In the XIX century, the districts of Galata and Péra were the most important trading areas of Constantinople. Galata, at the bottom, was where trading took pace, where the stock exchange and the customs stood. On the hill there was Péra, with its hotels, its embassies, its dwellings. To go from one district to the other, one had to go through very narrow and very sloping lanes, going up to 24 %, where circulation of vehicles was impossible.

To mitigate these difficulties of circulation and exchange, the French civil engineer Eugene-Henri Gavand have the idea, in 1867, to build an underground funicular tilted plan. 

In 1869 it obtains, after thousand and one adventures, from the Sultan Abdülaziz, the Emperor Ottoman, the concession for the construction of the underground funicular. 

May 8, 1871, a limited company, with the English capital, "The Metropolitan Railway of Constantinople from Galata to Pera" is founded and the first work began on June 30, 1971. 

May 5, 1874, work ends. The "Tünel" is built. Energy necessary is produced by two steam machines of 150 CV. 

Tünel will be brought into normal service only after one year of testing transportation with cattle. 

In end, January 18, 1875 it is opened with the public!

 The Tünel consists of a single brick-lined tunnel measuring 554.8 metres (1,820 ft) long, 6.7 metres (22 ft) wide and 4.9 metres (16 ft) high. It has one station at either end. The lower station is named Karaköy (located on the eastern end of Tersane Avenue at 41.0229°N 28.9749°ECoordinates: 41.0229°N 28.9749°E), and the upper station 

Tünel Meydanı - Tünel Square (located on the southern end of Istiklal Avenue at 41.0278°N 28.9719°E). The upper station stands 61.55 metres (201.9 ft) higher than the lower one. The slope of the tunnel varies along its length from 2 percent to 15 percent. It was originally built with two parallel lines,but now has a single track with a short duplex section in the middle, where two trains pass side by side.

 The parabolic profile met two aims: initially to immediately enter in underground, while reserving above the tunnel, greatest height of possible ground under the foundations of the houses; then to allow the down-train on the basis of Galata to start automatically by releasing the brakes, and without the help of the steam machine. Once the train moving, one gradually opens the vapor introduction to maintain the movement, which without that would not be long in stopping; because the train on the basis of charged Péra, can actuate the empty train of Galata, only over one length 390 m.

The line is with double track, and in straight line. At the top, and in the axis of each way, one placed a large grooved pulley 4,50 m in diameter. 

On each one of these large reels is rolled up a flat cable, whose end is fixed at the circumference of the pulley, and the other attached to the vehicle of the one of the tracks. These pulleys are fixed on the same shaft, the cable is held one while it is rolled up on the other. 

This use of reels placed in the axis of each way removes the return pulleys, necessary when the cable is rolled up several helical times around a drum. Instead of a round cable a flat cable was employed, which is placed more easily in the groove of the pulley, and the wear and tear of the cable caused by its rolling up is in particular decreased. On the other hand these turns of superimposed cables the ones with the others, offer a disadvantage: there is a very notable speed variation, due to the difference in diameter of the circumference which is held. By supposing a thickness of cable of 18 mm, a 600 m length; the maximum diameter is 6 meters, the minimum diameter is 4,70 meters for a mean velocity of 4 m per second, the minimum speed will be 3,56 m/s, and the maximum speed of 4,52 m/s, it is a significant variation [.. ] 

Each train is composed of two vehicles; ahead, a platform for the transport of the cars, the horses, the goods, and even of the travellers of 2nd class standing; behind, a closed traveller car, being able to contain 90 people. 

The platform, when it is not there vehicles or goods can carry 60 people. 

A train can thus transport 150 people [.. ] When the two cars pass each other, the free interval between them, is only 0,20 cm. This reduction is without disadvantage, the travellers entering and outgoing of the cars by the side external with the way, and them cars offering door only on this face there, are closed completely on the other face. "

 In 1911, the concession is transferred to the Company "Dersaadet Mülhakatindan Galata ve Beyoglu Beyninde Tahtel' arz Demiryolu" (Company of underground railway between Galata and Beyoglu). 

March 1, 1939, the government nationalizes the Tünel and transmits it to the IETT (Establishment of public transport with electricity of Istanbul). 

 November 3, 1971, after 96 years of service, the first funicular with cabins made of wood, with two parallel tracks and driven by steam machines, gave way to the new funicular which is still in service currently...