Piles, or cylinders, were driven into the sand, then cut to the right length. Later, concrete blocks were put on top to connect the piles. (Chesapeake Bay Bridge-Tunnel)

Chances are good that you will ride across a big bridge this summer. It will swoop up and over a large body of water, giving you great views of the sky overhead and small-looking ships below. You may also ride through a tunnel under a body of water, where it will be noisy and dark. Rarely are these two engineering feats combined.

But about three hours from Washington, you can ride on the Chesapeake Bay Bridge-Tunnel, which turned 50 years old this year.

It runs across a large water expanse with the Chesapeake Bay on one side and the Atlantic Ocean on the other. In 1964 it was named “one of the seven engineering wonders of the modern world.”

Ferry rides and choppy waves

Without the bridge-tunnel, your parents would have to drive hundreds of miles to get from Virginia’s Eastern Shore to the Norfolk-Virginia Beach area.

Before the bridge was built, ferries hauled 50 to 60 cars at a time, or about 50,000 cars a month, across the almost 18 miles of water. It took 90 minutes, and bad weather or choppy waters sometimes delayed the ferry.

The Chesapeake Bay Bridge-Tunnel goes underwater in two spots so ships can get in and out of the bay. (Chesapeake Bay Bridge-Tunnel)

As time went by, more people wanted to get across the bay quickly and on a reliable schedule. So in 1960, thousands of people began work on the engineering marvel. It would take them almost four years.

A bridge and a tunnel

How do you build a 17.6-mile bridge-tunnel that runs over and under water as deep as about 95 feet in some places and as shallow as four feet in others?

“They came up with a plan, or a set of plans, to build the bridge-tunnels,” said Bob Johnson, director of maintenance of the bridge.

First, engineers needed to figure out where the soil under the water was most dense. That’s where they could drive down the piles — the concrete cylinders that would hold up the bridge. They tested the soil by drilling pipe into different points in the bay floor and figuring out where the sand was the most resistant. That would help the piles stay in place. The ideal soil did not run in a straight line across the water; this is why the bridge curves.

They used a machine to drive the piles down into the sand. Then they cut each pile to the height called for in the plan and filled each one with sand and concrete. (About 5,000 piles make up the bridge-tunnel.)

The workers connected three of the piles sitting side by side by securing a concrete block on top of them. That’s called capping. The three piles together are called a bent. Once they had the bents ready, they could put on the road, whose pieces were made on land, shipped on a barge and placed on top of the bents.

The plan also called for two tunnels to provide gaps in the bridge allowing ships to get into and out of the bay. The tunnels, each about a mile long, are connected to the bridge sections at four islands that are each about as big as four football fields.

Connected by islands, tunnels run about a mile each under the bay. (Chesapeake Bay Bridge-Tunnel)

To make the tunnels, the workers first dug a ditch in the sand under the water and lined it with rocks. Then the tunnel, like the road, was delivered in pieces from a site on land. They lowered the tunnel pieces (plugged up, so no water would get in) into the ditch and connected them with concrete. They then unplugged the tunnel pieces so (of course!) cars could drive through.

The future of the passage

The bridge, which cost about $200 million to construct, was completed in 1964. But you could say that it’s never really complete. Johnson, who has worked on the bridge for 20 years, and his crew go out daily to check on the bridge structure, making sure it’s safe and functioning. Between 1995 and 1999, more roadway was added, making the bridge two lanes in each direction. In the next few years, a new tunnel will be built beside one of the originals; a second new tunnel is planned for 2030 or later.

On April 15, the Chesapeake Bay Bridge-Tunnel turned 50, and friends of the bridge threw a party. Even Virginia Governor Terry McAuliffe came.

A rest stop and a restaurant for tourists to stop and breathe the saltwater air awaits on one of the islands. Another island hosts a wildlife refuge that is not open to the public.

More than 100 million cars and trucks have traveled the bridge-tunnel in its 50 years.

To some, the bridge is beautiful, inspiring and a symbol of what people can do. But to people such as Johnson, the bridge is simply something necessary. It’s for someone who might need to go to the doctor’s office, buy school supplies or visit a friend.

“It links the eastern part of Virginia to the rest of Virginia, ” he said. Since there are no ferries running anymore, he added, “it’s the only way to get across the bay now.”

Learn more about bridges

People have been building bridges for thousands of years, and there are many different kinds of bridges. Part of the bridge portion of the Chesapeake Bay Bridge-Tunnel is a truss bridge, in which triangular structures above or below the bridge deck provide support. A beam bridge is a bridge where the roadway simply sits on top of heavy beams. A highway overpass is one example. And a suspension bridge — San Francisco’s Golden Gate Bridge is a well-known example — has hanging cables to provide support. A bridge in Boston, called the Zakim Bunker Hill Bridge, is a cable-stayed bridge, which has cables that run from the deck of the bridge to towers overhead.

Build your own

The United States Military Academy offers free software that challenges users to design a steel truss bridge that can carry two-way traffic across a river. It needs to be safe, but it also needs to stay within a budget. The software, which is used for an annual contest called Engineering Encounters, is geared toward students in middle school and high school. Find out more at www.bridgecontest.org. (Always ask a parent before going online.)

Moira E. McLaughlin