The corridor which extends approximately 450 km. between Riyadh, the capital of Saudi Arabia, and Dammam, the main Saudi port on the Persian Gulf, is part of the corridor which extends toward the West to the port of Jeddah on the Red Sea.  This corridor interests the most developed and most densely populated areas of the entire Saudi Arabian Kingdom.  In fact, in 1976, the year in which the S.R.O. began to sense the need to develop the Kingdom's railway network,  the Dammam-Jeddah corridor could already count more than 3 million inhabitants,  more than 43% of the nation's population.

In 1976, the only existing railway in the Dammam-Riyadh corridor was the single-track line connecting Dammam and Riyadh by an approximately 560 km. route through the towns of Dhaharan, Abqaiq, Hofuf, Harad and Al Kharj.  This line which was built in the distant 1930's  was  principally the result of the necessity to transport machinery and equipment via railway to the Port of Dammam which was then destined to the water wells of Al Kharj, one of the nation's most important water reserves.

The decision to build such a long route was the logical consequence of the need to serve the important city of Harad and to cross the dune desert of Dhana in its most narrow spot.  In fact, the desert was the most difficult environmental obstacle to construction and operation.

The Dammam-Al Kharj-Riyadh railway line had standard rail gauge and was run via a VHF radio system directly from the Central Office in Dammam through a direct radio contact between the controller and the driver. There were two passenger trains daily with a rather limited composition, one departing in the morning from Dammam and the other from Riyadh in the afternoon.  There was also one freight train daily  from Dammam to Riyadh with a variable composition of 40 to 60 wagons.

The operational and structural conditions of the railway certainly did not constitute an adequate base for the redevelopment of a new and more efficient railway service capable of handling a growing passenger and freight transport demand.

It was then that S.R.O. realized that it was necessary to begin contemplating the in-depth overhaul of the existing infrastructures and the simultaneous construction of new infrastructures.  Consequently S.R.O. entrusted Technital with the task of developing the final design and supervising the works for the renewal of the existing railway line between Dammam and Riyadh.

The final design foresaw the complete redesign of the horizontal layout of the alignment with the introduction of geometric elements suitable to modern operative standards. A topographic investigation was first launched to define the layout of the terrain and  the existing railway with the survey of the centreline every 50 m. in straight stretches and every 25 m. in curves.

Later, through a specific calculation program, the  geometric elements between the axis points surveyed were defined by computer, thereby allowing the definition of the geometry of the entire alignment, even through the introduction of transition curves not existing in the old infrastructure.  At the same time, the gradients were redefined and the permanent way was fully replaced.

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