Strait of Messina Bridge

The world's longest suspension bridge.

What: The world's longest suspension bridge

Where: Connecting sicily to mainland italy

Cost: $5 billion

Crux: A single 2-mile-long span. The 10-lane bridge would be capable of flexing 30 feet during earthquakes of up to 7.1 on the Richter scale.

During the Punic Wars, Roman consul Gaius Cecilio Metello
wanted to march elephants into Sicily across a wooden bridge; in 1870 a 2-mile tunnel was proposed to link the island with the mainland; and in 1971 a fixed link was declared a "prevailing national interest." But the area's 100 active seismic faults--including four directly through the Strait of Messina itself--and powerful winds and ocean currents have long been formidable engineering obstacles.

Italian prime minister Silvio Berlusconi pledged in June 2002 to build the bridge at last, but its construction remains a huge undertaking. Advances in computer modeling mean structures can be designed lighter and stronger, making possible a single 2-mile-long, 10-lane span suspended from 4-foot-diameter cables hanging from 1,000-foot towers built on the mainland and the island. The span would beat the current world-record holder, Japan's Akashi Kaikyo suspension bridge, by 66 percent. The land-based towers eliminate the problem of building support bases in the turbulent water; a suspension bridge allows the span to flex up to 30 feet during earthquakes. But the wind remains treacherous to the bridge and to large trucks and trains crossing it, says Khaled Mahmoud, director of long-span bridges at Hardesty & Hanover, a New York engineering firm that first began sketching Messina designs in 1969. Using computer and wind-tunnel models, engineers have designed steel box bridge sections that will act like giant aircraft wings to deflect the wind, mitigating the same vortex shedding that bedevils tall buildings. The bridge project remains stalled, however; the Italian government can't manage the enormous expense on its own, and private investors fret there won't be enough traffic to recoup their outlay.