A hybrid automobile started looking like a good idea to me in the late nineties, when Honda introduced the Insight and Toyota announced the Prius for the US market (they've been selling a version of the car in Japan for years already). As my previous vehicle began reaching advanced age, the reasons started accumulating.

• ULEV or SULEV - The air in the Triangle in the Summer is in the top 10 worst
• Low fuel consumption - price hike resistance
• Tax Break - $2000 at the moment (our government has decided to phase them out)
• Both the Toyota Prius and Honda Civic Hybrid are 100% practical, drivable vehicles (The Insight is useful too, if your needs match its capabilities)
• Test drove it; had a blast

This one is "blue moon pearl". Click a picture to see a larger version.

Starting with the power plant...

Toyota redesigned the Prius when they brought it to the US market. They bumped its electric motor up to 44 horsepower, which is enough to pull the car around by itself for low-speed maneuvering. Prius drivers call this "stealth mode" because the car is completely silent.

Toyota also upped the gas engine to a 16-valve DOHC VVT-i 4 cylinder, 1.5L engine that provides 70 horsepower. An ingenious planetary gear system combines the two in either series or parallel to achieve a maximum of 114 HP, which is not insubstantial in a small, relatively light vehicle. In raw numbers, the acceleration doesn't seem that great; however, when driving you realize that the power curve is a better guide. It's not like any single-engine vehicle.

Here's a look under the hood (click for an enlarged image)...

When you first step on the accelerator, the 274V primary batteries drive the high torque electric motor to get the car moving forward quickly. The gas engine, if not already running, cuts in quickly, and both the motor and the engine pull the car up to speed.

One reviewer at Edmunds summed it up this way:

"But the Prius' big trick is marrying this engine with an electric drive motor. That unit delivers 44 hp across a wide powerband (1,040 rpm to 5,600 rpm) and 258 lb-ft from 0 to 400 rpm. Together, the system produces enough oomph to propel the 2,765-pound sedan with élan in the city and at highway speeds up to 100 mph. And, even at that speed, it manages 23 mpg. Also, when we pressed the throttle at 70 mph, it still had a little left for passing."

Just starting the car is different. There's no starter motor to wear out. The electric motor doubles as the starter. You twist the key all the way and let it go. The car then starts itself; just a little bump and the engine is running. There's no way to grind this starter, because the Prius knows when it's running.

The Prius also knows when the gas engine is needed, and will turn off the gas engine when it is not. When coasting on level ground, sitting at a light, or rolling downhill, the gas engine cuts off unless it is needed to charge the batteries or turn the AC compressor. Even when it's running the engine is very quiet.

The battery pack is situated in the back of the trunk. It forms a little "bench" that makes a ridge across the back of the trunk, and is surprisingly small. There are a couple of fan vents on the rear window deck to help cool the batteries under heavy use; I haven't heard them run despite some long round trips up to Maryland. There is a small conventional 12V battery in a side compartment in the trunk. This is useful in case a jump start is ever needed.

Another clip from Edmunds:

The orange wires that are just visible under the hood are the ones that carry the 274V required to drive the electric motor. The large silver object with the Toyota Hybrid System label is the voltage converter. Below it are the electric motor and two generators. The gas engine is on the right below the air cleaner. This is the same engine that powers the Toyota Echo all by itself.

An article in IrishCar Magazine recently covered a Toyota Prius entry in a rally race from Sweden to Jordan.

The Prius uses an Electrically Controlled Variable Transmission (ECVT) that is unlike a conventional Continuously Variable Transmission, or CVT. There are no complex pulley and belt arrangments to wear out. The Prius uses a durable planetary gear system to couple the drive motor and engine in a way that effectively mimics the CVT: a smooth power curve from full stop to full speed, with none of the engine speed variation and "stepping" found in conventional automatic transmissions.

There's a great Article on howstuffworks.com that provides detail on the Toyota Prius Hybrid System, including animations and diagrams.