Sympathy for the Machine:
A User Experience Report on the 2004 Prius

Let's establish this first: I don't work for Toyota, and I don't own stock in them. But their product designers have done a fantastic job of introducing new technology to mainstream users in a usable, effective, and humane way. As a software designer who deals with similar issues, I think it's worth exploring what they've done.

For four days in November, I drove a rented 2004 Toyota Prius. In case you've been living on a desert island, that's the latest model of their hybrid car. It's more computer than car, actually -- software controls just about everything except the steering -- but it doesn't feel that way.

And that's key. The gas pedal, brake pedal, and general road handling feel comfortable and familiar, though the pedals drive systems that are built entirely differently from standard cars. The wheels are driven by an electric motor, which draws its power from a battery pack; the batteries get recharged by a standard internal-combustion engine, which is turned on and off as needed by a computer. Uphill climbs and hard acceleration cause the engine to kick in more power directly to the wheels. So when you put that pedal down, the expected thing happens: the engine revs and the car leaps under you. Quite satisfying, really.

The brakes are even stranger. Rather than using brakepads, much of the braking is done via the motor itself -- the wheels drive the motor "backwards," and the car's kinetic energy gets sent back to the batteries to recharge them. This regenerative braking is the car's biggest technical breakthrough, but you wouldn't know it from pressing the brake pedal. It feels just like every other modern brake pedal on earth -- firm, predictable, illusively linear. Their engineers must have worked terribly hard to make it feel like a mechanical brake!

So it's familiar. Ordinary non-early-adopter people can drive this thing and feel okay about it, because their primary driving skills transfer perfectly. But some aspects of the user experience are unfamiliar enough that you get a sense of "whoa, this is different!" The key is not a key -- it's basically a remote control -- and you start the car with the literal push of a button (a big, round, sculpted one right next to the wheel). Gear-shifting is done with a little dashboard joystick, not a big center-console column. Most interesting of all is "stealth mode," the silent motion of a car in which the engine is not running. Most Americans are really not used to that, and the coworkers and friends I've driven with think it's the coolest thing since sliced bread.

Transfer of skills for instant usability, check. Cool factor, check. Now what about other design considerations?

Ergonomically, the dashboard controls get mixed reviews from me. The joystick shifting is weird, because the joystick doesn't retain state; you shift gears by flicking it this way and that, and the stick always springs back to its center position. Disturbingly, you can accidentally shift into a different mode by bumping it wrong. (Did I say "mode?" I meant "gear." Same thing, I suppose.) Reverse gear causes a headache-inducing beeping; I guess you're not supposed to stay in reverse for long!

Climate controls and radio/CD controls are virtual -- there's a touchscreen in the center of the dashboard (more about that later) -- so you can't operate them without taking your eyes off the road. It's true that the virtual controls are much brighter and more clearly labeled than they would be if they were physical. But blessedly, there are hard "accelerator keys" on the steering wheel that can be used blindly. As in software UIs, duplication of function for different use contexts is sometimes the right answer.

Visually, the Prius looks pretty good, though its aerodynamic lines, snub nose, and high butt make it resemble a Star Trek shuttlecraft. That'll appeal to some market segments. In contrast, their color schemes are almost all "girlie colors," in my husband's terms -- periwinkle blue, seafoam green, beige, silver, etc. (Are they aiming at women buyers? It wouldn't surprise me.)

In terms of overall function, there's nothing a regular midsize hatchback can do that the Prius can't, and the price difference is negligible. So new users won't feel like they're sacrificing anything by buying one. I gather that this is a key part of Toyota's marketing strategy, but having driven one of these things, I think it helps with the user experience, too -- instead of feeling self-righteous but vaguely cheated, you can feel good about driving a car that's genuinely enjoyable.

Ergonomics, form, functionality. Check.

But there's more. I mentioned the touchscreen in the middle of the dashboard, with virtual controls on it. Well, the default screen for this thing is quite cool. It shows an animated real-time diagram of the car's powerplant: where is the energy going, and in what direction? Is the engine on? Is the motor turning at all? Are the batteries charged or drained? Is engine-braking refilling the batteries? It also shows your current MPG, changing by the second. An alternate screen shows a bar graph history of your MPG over the last thirty minutes of driving.

This is not just a geek's dream. It encourages you to know more about the inner workings of this car, rather than treating it as a mysterious black box. Just as important, it constantly gives you feedback on how well you're driving, if you pay attention. Are you getting the best performance out of the car?

You quickly learn that fast acceleration is bad: the engine always comes on, and your MPG drops like a stone. But coasting to a gentle stop is good, because you can see the car reclaim almost all that energy. It's especially fun to climb hills: to watch the numbers drop and the engine kick on (red arrows) as you start climbing, and then to see the engine shut off, the regenerative braking start (green arrows), and the MPG go to 99.9 (whoo-hoo!) as you zoom down the hill. As an early hybrid owner put it, feedback screens turn ordinary driving into "an eternal battle between Red and Green. Red is bad, because you're burning fuel. Green is good. I encourage green."

After a little while, you might feel visceral reactions. You start to feel pained when the MPG drops, and relaxed when the car coasts along silently with no engine. Subtle hills in the roads become noticeable, because you get feedback from the car that you'd never gotten before. I started to feel like a bicyclist -- straining up hills, coasting down them, and pushing to maintain high speeds against wind resistance. The feedback screens let you feel a sympathy for the machine as it does its work.

And thus your driving habits change. Normally, I'm a harsh driver; I accelerate hard out of stoplights, I drive fast, I close in behind slow drivers. But four days of driving a Prius seems to have changed my approach to driving. Even though my own car doesn't have feedback devices like the Prius's, I know now what these driving habits cost in terms of fuel economy. Quite an eye-opener, and I'm probably a better driver for it.

It should be pointed out here that little of the interaction design in this car is completely new. Red/green battles can be seen in both older Priuses and Honda hybrids, and some conventional cars have instantaneous MPG readings. The 2004 just pulls it all together into a package that works really well, and that appeals to the mainstream market.

Artifacts shape human behavior. The Prius is a fine driving artifact in general, and the design of its feedback screens shapes behavior in a way that is safer for drivers and better for the environment. It asks us to use our brains. And it fosters an emotional connection -- a real one, not one built on ersatz "style" or silly anthropomorphic agents. It's built instead on a thoughtful and honest construction of the human/machine interface, which encourages a deeper knowledge of, and partnership with, the car.

Congratulations to the 2004 Prius designers and engineers. While the 2004 Prius isn't perfect -- and nothing is -- they seem to have accomplished all that a product designer can hope for.

Now, about that months-long waiting list to buy one of these things...