A half-century ago ferryboats were banned on East-West routes in San Francisco Bay because they were deemed competitive threats to local bridge toll revenues.
Today, a motorist sitting in an idling car atop the Golden Gate Bridge at rush hour can't help but notice the empty blue bay and know the plan worked too well.
But the notion of reviving ferryboat competition and utilizing the ''unused highways'' of the bay is now being posed as a solution to lure commuters from clogged bridges and freeways.
''I felt like high-speed marine transportation was all Star Trek. But since we've been looking at this, I've found that there are 4,000 high-speed vessels in the world and we're in the dark ages in the Bay Area,'' says Marin County Supervisor Robert Roumiguiere.
Ideally, Mr. Roumiguiere says he would like to put 10 percent of Bay Area commuter traffic on the water.
Already a private ferry company that services one north-south route to San Francisco has launched service with a twin-hulled catamaran ferry.
This week transit officials were zipped on a cushion of air at motor-boat speeds from San Francisco to Alameda on a test run of a 54-seat Hovermarine ferry.
It took 17 minutes to travel directly over the water - much less than the time it takes to drive across the bridge and down the coast.
The $1.5 million experiment by Harbor Bay Isle Associates uses a chartered British Vosper Hovermarine vessel that developers say could operate without subsidy fares of $3.50 to $6 one way.
Five groups here have proposed new water commuter routes for high- speed craft built for passenger traffic. They would run at more than 25 knots an hour, or twice the speed of today's conventional ferries.
High-speed ferry potential is being widely reevaluated because of packed freeways and crowded transit systems, according to a study of 10 US cities issued this month by the federal government's Urban Mass Transit Agency (UMTA).
''Hot spots'' where ferry development is being pursued are San Francisco, New York City, Boston, and along the coast of Alaska, says Pat Cass, who prepared the UMTA report.
Although regional transit authorities are promoting the idea, most of the impetus for development of the concept has come from the private sector.
The burst of interest, says Ms. Cass, has corresponded with the incentives created by tax law changes in 1981 and 1982.
Though the consensus among authorities is that public transportation is a money-losing operation, many view the ferry business as potentially profitable.
Two conventional ferry systems operating on the north-south corridor, which is exempt from the ban on ferries elsewhere in the bay, are able to recoup losses by using the boats for off-rush-hour tourist cruises.
Hydrofoils rather than hovercraft would be the best craft to use on San Francisco Bay, says Nicolas Hetzer, whose company had been the lone voice for ferry service here since the mid-'70s.
Dr. Hetzer is now proposing four hydrofoil routes on the bay that would reach as far north as Pittsburg, 40 miles from San Francisco.
''I spent six years (promoting this), and there was no interest whatsoever,'' Hetzer says. ''They just tried to get rid of us politely. We get calls now every day from government and newspapers.''
Although there are several permit and legal requirements even to start these programs here, two of the toughest will be the East Bay ban on ferries and the federal Jones Act.
The ban on ferries is tied to the sale of bridge construction bonds in which investors were promised there would be no ferry competition.
The Jones Act prohibits the use of foreign-built water craft from operating commercially between two domestic ports.
A protectionist trade policy, the act would prevent the use of the advanced vessels built in Britain - a pioneer country in the high-speed water business - from being used in the Bay.
Locals are quick to point out the aesthetic value of commuting by ferry. And transit officials have no doubts it would be popular.
''When the bridge was completed in the 1930s, we (35 ferry companies) carried more people in an hour on ferryboats than in an hour on the (Bay) bridge today, '' says San Francisco Supervisor Quentin Kopp, chairman of the Metropolitan Transit Commission .