The Marmaray Project is named for the Marmara Sea, which separates the northern and southern passages of the Turkish straits, and from the Turkish word for "rail."

  The Turkish government on March 13 signed a loan worth 400 million euros ($477 million) with the European Investment Bank (EIB) to finance improvements on rail lines connecting to the tunnel and to buy equipment and materials for the tunnel project. To date the EIB has loaned over 1 billion euros to the Marmaray Project.

When completed by 2009 it will carry up to 75,000 passengers an hour.

  The whole Marmaray project, also financed in large part by the Japan Bank for International Cooperation with a budget of 2.5 billion euros, is part of a larger effort to upgrade 76 kilometers of the city's suburban rail line.

Ways and means:

  Istanbul's modern transport infrastructure, such as it is, has been built for the convenience of the modern automobile. Two suspension bridges span the Bosporus. They are the only way, apart from by boat, to cross the strait, but both are inadequate for the task of handling all the traffic. As it is, all commercial trucks must use the second bridge, which is part of the TEM, or trans-European motorway.

  All these modes of transport have proven insufficient to move hundreds of thousands of daily commuters in a city of 12 million people.

  The municipal government of Istanbul began to develop light rail systems only in the past 15 years as the city's population continued to swell and the roads became ever more clogged.

  Now a network of separate lines forms the city's rail system, including a short underground built by the French in 1875. Travelers can even take a metro line to Istanbul Atat International Airport if they can make it to a connecting station and get down the stairs with their bags.

Business people complain about the length of time it takes to get anywhere in Istanbul because of its enervating traffic jams. There are several options for solving this problem, including building a third bridge across the Bosphorus if agreement can be reached on where to site it, as well as extending the rail and tram systems and of course building more roads.

Technical challenges:

  Dredging and drilling platforms float near Istanbul's iconic Maiden's Tower, just across from the Golden Horn, preparing to immerse tunnel sections in the seabed for the intercontinental tunnel.

  Archaeologists oversee the digging on shore, where the project cuts across the oldest part of the city. This issue has particular resonance in Istanbul because the city is so old and historic. Even extending the metro line from the city center has been delayed because trial runs under the historic Pera district caused cracks in the walls of former embassies and other old buildings.

  Most of that area's historic buildings date only from the 19th century, but the old city has structures of incomparable heritage, including the 1,500-year-old Haghia Sophia. As planned, the Marmaray line will go underground at Yedikule, which marks the farthest reach of the ancient Theodosian walls where they meet the Marmara Sea.

  The inter-continental rail line will then cut across the historic peninsula to connect with a station at Sirkeci, the last European stop on the Orient Express, before crossing under the sea to connect with the old suburban line to Istanbul's far eastern reaches.