The future seemed very close when GM showed off Electrovan - in 1966, only to permanently garage it because nobody could afford it.
Is it any closer now?
I gunned GM's fuel-cell version of the Chevrolet Equinox onto the Jones Falls Expressway. The retrofitted sport utility vehicle is as powerful as you could wish and, lacking pistons, a transmission or even a combustion chamber, quiet as a baby buggy.
But despite GM's aggressive push to get these cars into America's driveways, the future will have to wait a while longer.
The car is here - made available by GM so a new generation of writers can go gaga. But the hydrogen economy needed to fill it up isn't. Until the average driver doesn't have to burn half a tank of hydrogen traveling to the pump, fuel cells will be like solar panels and electric wind farms: expensive exceptions in a fossil-fuel- powered world.
GM knows this, which is why it's getting stations to install pumps and pushing Congress to grease the process.
Without a network of hydrogen tanks, nobody will buy the cars. Without any cars, nobody will build the tanks.
At next week's Washington Auto Show, the company will demonstrate a prototype like the one I drove - there are about three dozen now - and announce two local families who will get to keep and drive one for a few months. (There's a Shell station near Washington with a hydrogen pump.)
The goal of "Project Driveway" is to get as many as 100 fuel-cell loaners placed with households in Washington, New York and Los Angeles.
If anything, experts are surprised the technology has developed this fast.
Despite decades of research costing billions, companies even a couple of years ago were having trouble making fuel cells small, powerful and reliable enough to drive a mass-production car. One problem, which GM appears to have overcome, was getting vehicles to start in cold weather.
"You were driving it - that's a lot different than something in a couple of test tubes," said David E. Cole, chairman of the Center for Automotive Research in Ann Arbor, Mich., on the phone yesterday. "It doesn't mean the economics are there ... but this is moving pretty fast right now, maybe a little faster than people thought."
GM is coy about what the car might cost. But the decision to introduce the prototype as an Equinox - bearing the moderate-priced Chevrolet marque - wasn't an accident, company representatives said.
A mass-production GM fuel-cell car is likely to be smaller than an SUV - probably in the Chevy Volt frame that's also being considered for ethanol and plug-in electric versions. In any body, Cole thinks, a fuel-cell car could sell for less than $40,000. Honda has said it will lease fuel-cell cars in Los Angeles this summer for $600 a month.
That's not bad for NASA technology - even 40 years later. If all goes well, "early adopters" will embrace fuel-cell cars by GM, Honda, Toyota and others, financing further development, spurring pump installation and generating a virtuous cycle of investment and lower and lower prices.
The technology certainly seems ready, to judge from the Equinox with 800 miles on the odometer I drove. Expecting a golf-cart effect, I was surprised by the zip and responsiveness. Fuel cells peel electrons off hydrogen atoms to drive an electric motor connected to the front wheels.
There is no transmission, which means that, if this really is the car of the 21st century, GM's Allison Transmission plant in White Marsh will have to find a new line of work. There is no spark, no flame. The only exhaust is water vapor.
But there are challenges beyond pump scarcity. It's far from clear that hydrogen will be cost-competitive with gasoline as a fuel. The Equinox's range is 200 miles, tops. The fuel cells must be replaced after 50,000 miles. How much will that cost? Industry claims of modern hydrogen safety ring true, but the image of the hydrogen-powered Hindenburg going down in flames is hard to erase.
And while the Equinox is pollution- and carbon-free on the road, the hydrogen that propels it is extracted from fossil fuels with huge amounts of electricity, which also is largely derived from fossil energy. GM says natural gas will be a relatively cheap and eco-friendly source of hydrogen.
Technology likes to move in measured steps, not leaps. Going from gasoline to hydrogen is almost as far as going from steam to gasoline. Someday fuel-cell cars may be an economic staple, and if they are GM will be rewarded.
Because the company is years behind Toyota and Honda in developing hybrid gas/electric vehicles - which GM boss G. Richard Wagoner Jr. admits was one of the company's biggest mistakes - the stakes for it are especially high.
But the fuel-cell future poses no threat to the Allison plant anytime soon.