billion dollar infrastructural undertakings that, when completed, play a major role in organizing our daily lives. They serve as vital conduits for the movement of our cars, trains, and water; they transport the gas later burned to create our electricity and heat; they allow for the shipping of goods from one side of the planet to the other. Many of the world's most iconic megaprojects were built in the first half of the 20 century. Here is a sampling of five of the world's most expensive and complex projects underway today. 1. The world's longest overwater bridge: Qatar-Bahrain Friendship Bridge Qatar and Bahrain are separated by just 25 miles of the Gulf, but because the former country is a peninsula connected to Saudi Arabia and the latter an island, getting from one to the other via road takes five hours. The Qatar-Bahrain Friendship Bridge will cost $2 billion to build and work is expected to commence later this year. Though the initial plans included only a road connection, a rail link along the corridor that would add $5 billion to the price tag is now being studied. The cable-stayed bridge should be complete in 2013, and reduce the commute between the two countries to half an hour. Though the project will be the world's longest overwater bridge, 6,000 people are expected to use it each day. 4. The world's longest natural gas pipeline: The Trans-Afghanistan that would transport the gas from the shores of the Caspian Sea to the Indian Ocean. Turkmenistan has some of the world's most plentiful supplies of natural gas, but its resources haven't been exploited to their full potential because of the political and economic volatility of the surrounding region. The 56-inch pipes won't be built in a day, though. At 1,040 miles, the corridor stretching across Afghanistan will be one of the world's longest and cost $7.6 billion to construct, if the funding can be secured. The Asian Development Bank leads the project's development and is still negotiating with the shaky Afghan government, which would receive transport fees through the deal. 3. Expanding the Panama Canal Before 1914, freight-laden ships needed to sail around the tip of South America to get from the Atlantic Ocean to the Pacific. The carving of the Panama Canal cut down trip distances dramatically - from 14,000 miles between New York and San Francisco before to 6,000 after. The project, then, was a brilliant innovation in reducing the cost of international trade. In fact, today it's so popular that it's rapidly running out of space: by 2012, there's likely to be more traffic than the canal can handle. In response to the oncoming logjam, in 2006, Panama's voters endorsed a $5.25 billion plan to double the artificial river's capacity by 2014, and the country began preparations in 2007. The project will be one of the largest canal programs in human history, employing up to 40,000 construction workers building a 4 mile-long access channel and brand new locks on both the Atlantic and Pacific. Once the dredging is done, there should be few capacity problems for decades. 4. The world's longest tunnel: Gotthard Base Tunnel Switzerland lies at the heart of European trade routes, from Italy in the south to Germany in the north. But transporting freight and passengers across the country isn't so easy because of its mountainous landscape, which creates winding, slow-moving roads. In 1994, the country's voters elected to fund several new railway tunnels under the Alps that will dramatically improve the situation. The largest element of the plan is the Gotthard Base Tunnel, which will run more than 35 miles when it opens in 2018 and claim the crown of world's longest tunnel. Construction on the $6.4 billion project began in 2003. More than 2,000 workers labor daily to make it a reality. The project is run by AlpTransit, a wholly-owned subsidiary of the Swiss Federal Railways.
