TOKYO (AP) -- Your hands don't even need to be touching the steering wheel for it to start spinning back and forth aggressively, all by itself _ slowly guiding the car into the parking spot.

This is a bold and somewhat unnerving concept, a car that parks itself. As a driver, you've got to wonder as the Prius eases back toward the curb: What is this machine thinking?

It's also difficult not to be gripped by a "Look Ma, no hands" thrill -- even if the system only partially fulfills its promise.

But we'll get to the drawbacks later.

First, the logic behind this innovation.

If you know Japan, it should come as no surprise that about 80 percent of its Prius buyers have opted for Intelligent Parking Assist. This is a country of famously narrow streets and cramped lots where squeezing into spaces can be a blood pressure-raising exercise.

In the United States, by contrast, there's generally plenty of room for no-sweat parking and so it's unlikely Toyota will offer the feature there, says Akihiko Saito, a company executive vice president. (Some U.S. city-dwellers might disagee).

Parking Assist relies on a built-in computer, steering sensor and a tiny camera in the car's rear and works like this:

A dashboard display shows the image taken by the camera. When you near a parking space and shift into reverse, computerized lines pop up on the display, along with arrows pointing up, down, left and right.

Using the arrows, you move the lines around until they define exactly where you want the car to be parked. Then you push the "set" button on the display.

Keep your foot lightly on the brake pedal, and the car will start backing up, the steering wheel responding to an invisible hand. Voila, the car will park itself in the spot you've chosen with the arrows.

Have no illusions, however.

Hands-free driving doesn't mean you can read a book or doze off. The system has no artificial intelligence that actually recognizes objects -- so it won't stop for a person or a cat or anything else you shouldn't be running over.

You still have to hit the brakes yourself. And the system is designed so that it will shut itself off if you lift your foot from the brake pedal, making the car go too fast.

Intelligent Parking Assist also will back you into a garage, and can "remember" three parking spots.

And now for the major limitation: The system works only in situations where the car can continuously back up into a space -- not for those tight spots where you must inch your way into a space by going back and forth, wrestling with the wheel.

Unfortunately, such spots are quite common in Japan. And that's precisely when you wish you had a smart car that would graciously help you park.

For me, the parking system also took some getting used to.

You can't turn the car too much before you start parking because the car will get confused and tell you to start over. You must decisively glide straight into pre-parking position before the car will let you begin jiggling the arrows on the panel.

When I tried the system in our tiny parking lot at home, the system kept flashing warnings on the screen that the car was too close or too far from where I wanted to park.

A tutorial at a Toyota dealer is recommended.

Toyota is considering offering Intelligent Parking Assist in other models in Japan but has not decided which ones.

Among helping technologies it has already made available in Japan are an automatic anti-collision system, in which seat belts tighten and the car brakes harder in anticipation of a crash.

Toyota plans to offer that feature later this year in the United States. Honda Motor Co. offers a similar system in Japan but not in America.