The current bridge is believed to have been built in 1864, for about $3,000.
This makes a tunnel somewhere between 6 and 7-1/2 milonglong; the current bridge is 3.1 miles long.
This setting (the current bridge was built in the 1920s) captured Eakins's eye; one pier of the previous bridge figures prominently in "The Pair-Oared Shell".
The study will initially consider 80 alternatives to the current bridge that local residents, officials, environmental groups and others have proposed.
According to the agency's preliminary estimates, it would cost $1.1 billion to rehabilitate the current bridge, and about the same to replace it.
But the owner of the current bridge, the Ambassador Bridge, is moving ahead with a plan to build a new, privately owned bridge to replace the one he owns.
Mr. Breen said it would actually consist of two identical bridges, one for northbound traffic and one for southbound, each with full shoulder-breakdown lanes, which are missing from the current bridge.
For one thing, they say, the current bridges are already exceeding capacity, as put on vivid display when a crack was discovered on the double-deck I-64 bridge in 2011, closing it temporarily.
Hazel Morton, 81, who has lived in the valley since 1952, long before the current bridge was built, said that every six months or so bodies would fall into her neighborhood.
The current bridge charges $3.75 for cars; trucks (about 12,000 of which cross here each day during the busiest part of the week) pay by weight, averaging, Mr. Stamper said, $12.
