For water crossings, a tunnel is generally more costly to construct than a bridge.
For weight capacity reasons it may be more feasible to build a tunnel than a sufficiently strong bridge.
For aesthetic reasons choosing a tunnel instead of a bridge is a better idea in order to preserve the above-ground view, landscape, and scenery.
Another problem is that bridges usually require a larger footprint on each shore than tunnels.
There are a mixture of bridges and tunnels, such as the the Chesapeake Bay Bridge-Tunnel in the United States.
The Chesapeake Bay Bridge-Tunnel (CBBT) is a 23 mile (37 km) long facility that connects the Delmarva Peninsula with southeastern Virginia.
It was opened on April 15, 1964. Since 1964, more than 67 million vehicles have crossed the Chesapeake Bay Bridge-Tunnel.
