Google just introduced its prototype of a self-driving car but already people seem ready to abandon the metro’s long-standing plans for mass transit. What is the point of building a multi-billion dollar light-rail and express bus system, they ask, when the new technology will allow commuters to sit back — even lie down — in vehicles that will magically whisk them wherever they want to go?

While Google has unveiled its model — a two-passenger thingie that looks something like an amusement-park ride — it estimates that production won’t take place until 2020. The company has a greater interest in selling its software than in producing cars. Conventional carmakers like General Motors, Volvo, Nissan and Audi have also been working on driverless cars using vehicle-to-vehicle communications systems that would allow cars to travel together at high speed.

In fact, many cars on the road now have autonomous features like cruise control, blind-spot sensors and forward-collision warning systems (to keep you from crashing into an obstacle). The 2014 Mercedes-Benz S550 can virtually drive itself in congested traffic. And for years ahead, most vehicles will offer more and more such features, but, says Rik Paul, auto editor at Consumer Reports, “The truly driverless car is so far down the road that right now, it’s just a vision.”

At this point, we don’t know which of the many products in development will capture the market, what it will be like or how much it will cost. Remember the video-recording war between Betamax and VHS? It took 10 years for the latter to completely vanquish the former, and today, of course, both are obsolete technologies.

So how might the so-called autonomous car change our lives — and the shape of the city? Here are some thoughts:

Fewer accidents

Self-driving cars could reduce accidents and highway fatalities. In 2012, the most recent year for which statistics were available, there were nearly 40,000 car accidents in the Twin Cities seven-county metro. Most of those were probably minor, but 101 people lost their lives and nearly 14,000 suffered injuries. Depending on which study you look at, driver error is the cause of 90 to 99 percent of accidents. While nobody asserts that the driverless car would eliminate all of them, it could do away with many common causes: distracted driving, drunkenness and inexperience. In theory, safer roads could encourage more folks to walk or use a bike.

BUT, assuming that for the next 10 or 20 years we will be dealing with ahybrids of the driverless car — one that works without an operator but only on the highway, for example — drivers will still be crucial to safety. The safety features, however, could lull them into inattentiveness, making cars more dangerous. And, knowing individualistic Americans, some will want to turn off the safety features or make their use optional.

Less stress

Commuting would be stress-free. On their way to work, passengers could read, work, make phone calls and put on makeup. And nobody would risk poking an eye out with the mascara brush since robot-operated cars would presumably travel at steadier speeds.

BUT, if driving becomes so enjoyable, allowing people to loll in their cars watching movies or ordering shoes on the Internet, they’ll spend more time on the road — and won’t mind long commutes. That would further crowd the roads and increase urban sprawl.

Help for people with disabilities

People with disabilities would be able to drive. Google’s prototype has no gas pedals or steering wheel, just and on-and-off switch. No longer would adult children have to take keys away from their elderly parents. Even the blind might be able to drive. Independence of movement might diminish the need for specialized housing or services like MetroMobility.

BUT unless the cars are voice-operated, some disabled passengers won’t be able to type in destination instructions.

Improved fuel efficiency

Fuel efficiency would improve. Supposedly, the automated car would save gas (if that’s the fuel it uses) because, with its various sensors, it could avoid traffic congestion, drive faster and closer to other cars on highways, presumably drafting them, and find available parking spots through an app. In the most evolved system, you wouldn’t even own a car; you would simply summon one to your house to convey you and perhaps a couple of other passengers to your destinations. Drivers would no longer waste fuel trolling for parking spaces, and, in fact, since cars would be shared, there wouldn’t be as much need for all those ugly parking lots where vehicles spend 90 percent of their time.

BUT already ordinary cars have improved fuel efficiency tremendously, and it’s not certain that autonomous cars would do better. “Fuel efficiency is not what people are discussing,” says Rik Paul. Most carmakers have been testing their driverless sytems on ordinary cars — the Lexus, the Mercedes-Benz and so on — which will get the same miles per gallon they do now. (Google’s Disney-like ride is too lightweight to be road-worthy.)

What’s more, the ability to draft other cars, adds Paul, “is way off in the future.” And there is no proof that car-sharing will become any more popular with driverless cars than it has been with driver-operated cars. After all, there is an already available way to have a car drive you door-to-door; it’s called the taxi. Without car-sharing, we’ll continue to be stuck with all those surface parking lots, which absorb heat, cook pollutants into a noxious brew and collect extra millions of gallons of storm runoff.

No mass transit

With driverless cars, we won’t need mass transit. Light rail and express bus systems will indeed become obsolete when everybody has access to a driverless car. After all, why would anyone hike to a station, ride stuffed next to a bunch of other folks who might smell bad or chew their nails when he or she can ride in exquisite solitariness doing absolutely nothing?

BUT, we don’t yet know how much the driverless car will cost. Manufacturers have kept mum about price tags, and Google is said to have incorporated about $75,000 worth of technology into its model. Not everybody can afford to own cars now, and those who do pay a tremendous portion of their disposable income buying and operating them.

In any case, we should remember that new technologies don’t automatically replace old ones. Yes, it’s true that buggy whips and typewriters are now museum pieces, but the invention of the television did not stop people from going to the movies or listening to the radio. And, even though the Internet allows folks to order whatever they want without leaving home or getting out of their bathrobes, they still go to brick-and-mortar stores to shop. To be competitive these days requires operating in every channel. So if they mean to grow, cities will have to offer all kinds of transportation — cars, light-rail, buses, bikeways, sidewalks, trams, taxis and car-sharing.