One of the more impressive engineering feats on the East Coast is the Chesapeake Bay Bridge-Tunnel ($15 toll in peak season), which opened in 1964 at the mouth of the Chesapeake Bay and was effectively doubled in 1999 by the addition of an extra set of driving lanes. Almost 18 miles long, the structure consists of one high-level bridge, two deep tunnels, four islands, and many miles of raised causeway. Southernmost Sea Gull Island closed to the public in 2017 as the construction of a parallel tunnel began; completion is anticipated in 2022. The existing bridge-tunnel will remain open to road-trip traffic.