ISTANBUL is one of the world's mega cities with a population of 13.2 million. Anyone who has visited this ancient city will be stunned by its spectacular location on the Bosphorus but shocked by its horrendous traffic jams. At its worst, journeys from one part of the city to the other have to be measured in hours rather than minutes.

While there has been investment in rail transit, this has tended to be in disparate projects, so that currently the 75.3km rail transit system is made up of 15 lines, and only on the European side of the Bosphorus. For example, the city's only heavy metro line connects to a conventional tram at Taksim which links to a funicular and then to a modern tram line. This crosses the Golden Horn to connect with a suburban line at Sirkeci station and a light metro line - quite a rich mix of rail modes in a trip of just a few kilometres.

But this is set to change as the pace of expansion accelerates with six new lines totalling 51.45km under construction, and another five lines comprising 84.5km at the tender stage. Studies on a further 25 lines are underway which would add a massive 301km to the transit network. The new lines under construction are a mixture of heavy metro, light metro and light rail, with the majority of the work again taking place on the European side of Istanbul.

At present, the only railway on the Anatolian (Asian) side of the city - apart from a 2.6km circular tram in Kadiköy - is a commuter line running east from Hydarpasa station. But this spring the first of two new metro lines is due to open. The 21.75km 16-station line runs from Kadiköy to Kartal, and is entirely underground including the depot, which has 16 stabling tracks, four maintenance tracks, a train washer, and a 1km test track. The 4km of track in the depot are designed for driverless operation except in the maintenance area. A fleet of 30 trains has been supplied by CAF, Spain.

Thales, working with Savronik, Turkey, has installed its Seltrac moving block communications-based control system (CBTC), which will allow attended ATO, automatic restarting of trains, and driverless parking. The line is prepared for driverless operation, but this will require the installation of platform screen doors. The metro has a design headway of 90 seconds and a service headway of 2 minutes to achieve a design capacity of 70,000 passengers/hour/direction.

The line is equipped with Tetra radio, an IP-based CCTV system, and is electrified at 1.5kV dc with a rigid overhead line power supply.

The total cost of the project is €751.3m, but a 3.4km extension from Kartal to Kaynarca is under construction, which will add another €150.2m to the cost.

Istanbul Metropolitan Municipality (IMM) is about to award a contract to build the second Asian-side metro: a 17km line, with a 2.7km underground link to its depot, from Üsküdar via Ümrayiye to Çekmeköy. Seven consortia tendered for the contract and Dogus Insaat ve Ticaret submitted the lowest bid at €563.9m.

The project is being funded through a €500m credit agreed with IMM by European banks. The contract will include all civil, electrical and mechanical works, construction, installation, testing and commissioning, as well as maintenance and operation supervision during the first two years of warranty. The line will open 38 months after contract signature. However, the fleet of six-car trains will be procured by IMM under a separate agreement, for which specifications and tender documents are being drawn up.

There are many similarities between this line and the Kadiköy - Kartal line which it parallels to the south. For example, it will be entirely underground with 16 stations, it will be electrified at 1.5kV dc with rigid catenary, and will have a design headway of 90 seconds. However, this will be the first metro line in Turkey to have unattended operation using CBTC, which will necessitate the installation of platform screen doors. This will also be a light metro as its design capacity will be 60,000 passengers/hour/ direction.

On the European side, Istanbul's original heavy metro line, which ran from Taksim to 4 Levent, has already been extended north and south and upgraded. The line now has CBTC, a new train control centre and a depot - for the first 10 years of its life one platform at 4 Levent station was used for maintenance. Construction is underway of further extensions to the north, and south across the Golden Horn to what will eventually become a major rail interchange at Yenikapi.

The Aksaray - Esenier light metro line is being extended 5.6km west to Bagcilar where it will connect with a new 15.9km heavy metro line under construction from there to Ikitelli, Olympic Village and Basaksehir. This line will have the same capacity as the Kadiköy - Kartal metro.

Istanbul's separate transit systems each side of the Bosphorus will finally be connected when the first phase of the Marmaray rail link currently under construction opens in October 2013. This comprises 13.6km of tunnels and three underground stations at Yenikapi, Sirkeci and Üsküdar. The tunnel will connect the existing commuter lines on the European and Asian sides which are being upgraded to form a single 76.3km line from Halkali to Gebze. The project took a major step forward at the end of last year with the award of a €1bn civil/electro-mechanical contract to a Spanish consortium to upgrade and equip the line.

Currently it takes about 3 hours to travel from Halkali to Gebze using a mixture of trains, taxis and ferries, but this will be cut to 1h 44min when the Marmaray project is complete. By this time, Istanbul will have a comprehensive and connected rail network of which it can be justly proud.