Engineers in Turkey have managed to successfully construct a tunnel beneath the Bosphorus Strait – a feat which defied the most ingenious minds of antiquity.
While building a tunnel beneath the Bosphorus Strait of today's Turkey has long been the ambition of emperors and sultans throughout history, it is only now in the early 21st century that engineering technology has finally developed to the point where such an epic project can become a reality.
The new 13-kilometre Marmaray tunnel, which runs below the Bosphorus Strait between the Kazlicesme and Ayrilikcesme stations in Istanbul, may be the final realisation of a dream cherished by Roman and Turkish rulers for many centuries, yet it took engineers from Siemens only two months to complete once work began in earnest.
Following a delay of four years in the commencement of construction due to the discovery of Byzantine archaeological remains in the excavated soil, the Siemens team was given just six months by officials last year to finish the first phase of the project.
That brief schedule was tightened even further to a mere two months due to the government's desire for the Marmaray tunnel to be up and running by the 90th anniversary of the Republic of Turkey.
"That was a challenge, but we met it successfully," said Javier Raposo of Siemens Rail Automation in Istanbul.
Construction of the tunnel was hugely challenging and complex given the huge volume of passenger traffic expected, as well as the susceptibility of the area to heavy earthquakes.
Trains run through the tunnel at two-minute intervals in order to maintain a passenger flow of around 75,000 people per hour when operating at maximum capacity - the equivalent of one million commuters in a single day.
This rapid-fire rate of movement was achieved via the deployed of a "moving block system," comprised of several sophisticated systems for the comprehensive signalling and control of all vehicles. The system is capable of gathering data on the velocity and location of each individual train via small sensor plates embedded in the tracks, coordinating the movements of the entire fleet of vehicles, and providing reciprocal feedback on the speeds at which each of them are permitted to travel at which segments of the tunnel.
This essentially means that the movements of each train running on the system can be automatically adjusted depending on the locus and speed of its peers.
"The crucial feature of our train control system is that it knows what conclusions must be drawn on the basis of the information," Raposo said. "It always knows how fast each train is traveling, when it stops, and when it starts up again it knows the positions of the individual trains, and it recalculates the driving speed and braking distance for all the CBTC trains that are on a given route."
The need for efficient tunnel transportation beneath the Bosphorus is keener now than ever before given that approximately a third of Istanbul's 15 million-strong population traverse it during their daily work commutes, yet were previously only served by a ferry service and three highly congested bridges.
The opening of the MarmaRay means Istanbul commuters will now be able to travel between Europe and Asia in just five minutes.
In addition to providing far greater convenience to Istanbul commuters and lightening the city's traffic burdens, the tunnel is also a marvel of seismic-proof engineering, capable of withstanding earthquakes measuring up to nine on the Richter scale.
Additional measures have also been introduced to preserve the lives and safety of commuters in a worst case scenario. Sensors trigger an alarm should an earthquake or water ingress occur, shutting gates at either end of the 1.4-kilometre segment of the tunnel which runs beneath the seabed, as well as compelling trains to stop prior to reaching it.
Turkish officials hope the tunnel, which is the first standard gauge rail connection between Europe and Asia, will have a transformative impact upon commerce and transportation in the nation's biggest city. The government has billed it as "the tunnel of the century" and is now avidly promoting its potential to become "China's non-stop connection with Western European markets."