Chesapeake Bay Bridge-Tunnel

Distinguished as an ‘Outstanding Civil Engineering Achievement’ by the American Society of Civil Engineers in 1965, the Chesapeake Bay Bridge-Tunnel is nothing short of a modern engineering wonder. Dipping over and under open waters with a complex chain of artificial islands, tunnels, and bridges, the Chesapeake Bay Bridge provides a direct link between Southeastern Virginia and the Delmarva (Delaware, Maryland, and Virginia) Peninsula. The bridge-tunnel complex is 17.6 miles long from shore to shore, and it cuts 95 miles from the journey between Virginia Beach and points north of Wilmington, Delaware.

The majority of the bridge-tunnel complex is above the water, supported by more than 5,000 piers. But due to the importance of shipping in the bay, the crossing was sunk deep beneath the bay in two mile-long tunnels, to allow the passage of ships. Four artificial islands, each with approximately ten acres of surface, provide the portals by which the road enters the tunnels. It’s quite an eerie experience to be driving along and see the road you’re on disappear into the bay. Millions of cars have crossed the Chesapeake Bay Bridge-Tunnel since it opened in 1965. It’s possible that many just crossed it for the thrill of it!

Holland Tunnel

By the early 1920’s, ferries across the Hudson River, the only mode of travel between New York City and New Jersey, strained to handle more than 20,000 vehicles a day. Fed up with the traffic congestion to and from the city, New York City officials decided to build an automobile tunnel under the Hudson River – one that would double the daily traffic load across the river. The biggest challenge was ventilation. Without some way of eliminating all the poisonous carbon monoxide from the automobiles in the tunnel, most drivers would pass out before reaching the other side!

Engineer Clifford Holland came up with a brilliantly simple solution: big fans. Inside four massive ventilation buildings on both ends of the tunnel are 84 powerful electric fans that draw fresh air into the tunnel and blow dirty air out. Each fan is 80 feet in diameter. That’s almost as tall as a 10-story building!

Unfortunately, fans this big can also be quite dangerous. In 1949, a chemical truck loaded with 80 drums of carbon disulfide exploded in the tunnel, injuring 69 people and causing $600,000 in damage to the structure. The ventilation buildings actually fanned the flames of the fire. As a result, strict standards were established in tunnels throughout the world for the transportation of chemicals and explosives.

New York Third Water Tunnel

Six hundred feet below the busy streets of New York City, engineers are boring a 60-mile-long tunnel – the largest tunnel in America. This tunnel won’t carry cars, trains, or even people, but it will deliver 1.3 billion gallons of water daily to nine million area residents. New York City’s $6 billion Third Water Tunnel is one of the nation’s largest and most complex public works projects ever attempted.

In 1954, New York City recognized the need for a new tunnel to meet the growing demand on its 150-year-old water supply system. Construction began in 1970 on the Third Water Tunnel, a tunnel designed to improve the dependability of New York City’s entire water supply system. The majority of the tunnel is being carved with a 450-ton, 19-foot diameter rock-chewing device called a tunnel boring machine. Unlike the older water supply tunnels in New York City, water control valves in the Third Water Tunnel will be housed in large underground chambers, making them accessible for maintenance and repair.

When completed in 2020, the size and length of the Third Water Tunnel, its sophisticated valve chambers, and its depth of excavation will represent the latest in state-of-the-art tunnel technology.