Detroit: The New, Improved Prius: Toyota tweaks its iconic hybrid

"If it ain't broke don't fix it" the adage may say. "But by all means improve it," Toyota might reply. Particularly in the case of this - the third generation Prius.

Outwardly the 2010 Prius exhibits only subtle refinements to what Toyota, not without justification, terms its "iconic" shape. As ever, aerodynamics dictate much of the wedge-shaped form.

Although overall height remains the same, the profile has been altered by moving the top of the roof 3.9 inches towards the rear, simultaneously emphasizing the wedge shape, improving aerodynamics and adding more rear head room to a vehicle that boasts five more cubic feet of interior space than the current model.

Additionally, new underbody panels, sharp corner edges, a longer rear spoiler and attention to details in the wheelhouse liner and wheels themselves contribute to a coefficient of drag of .25 (compared to the current model's .26) on what Toyota says is the "cleanest aerodynamic profile of any mass-produced vehicle in the world."

As for the running gear, the 2010 Prius features a powertrain that is 90-percent newly developed, including a new, beltless 1.8-liter four-cylinder gasoline engine that produces 98 horsepower and operates at lower RPM than its predecessor. Hybrid components including the inverter, motor and generator are smaller and lighter, while an exhaust heat recovery system, exhaust gas recirculation and an electric water pump help create 134 net horsepower.

Additional weight savings were found in the transaxle, which also reduces torque losses by as much as 20 percent compared to the current Prius, as well as the use of aluminum on the hood, rear hatch, front suspension axle and brake calipers and high tensile steel in the central pillar and roof reinforcement.

All told, the weight savings, smoother shape and improved powertrain result in a 0-60 mph time of 9.8sec, more than a second faster than the current Prius - all this while achieving an estimated 50 mpg with the car in "Eco Mode", one of three driving settings on the Prius (the others being EV-Drive Mode, which allows driving on battery power alone at low speeds for about a mile, and Power Mode for maximum performance). The 50 mpg mark represents an 8-percent improvement over the current model and a whopping 18-percent improvement over the original 41 mpg Prius.

Other noteworthy features on the 2010 Prius include disc brakes front and rear (replacing the current front disc/rear drum layout) and improved stability as the result of an improved stabilizer, higher caster angle and tuned-bushing.

Electric power consumption has been reduced through the use of optional LED head lamps and an ingenious system that enables the solar roof to power a ventilation system in hot weather, enabling fresh air to circulate while the car is parked, easing the strain on the air conditioning system and, thus, conserving battery power. In addition, Toyota's new Safety Connect safety and security service will be available a few months after the new Prius' launch.

Speaking of which, the 2010 Prius will go on sale in the United States and Japan in late spring, followed shortly by Canada and other countries. Sales target for the first full year of availability in the U.S. are for 180,000 units - up from the 160,000-some sold in 2008 - with a global objective of 400,000 cars in 2010.

All told, more than a million Prius have been sold since 1997 and have logged a combined 37 billion miles. And with this fourth generation Prius poised to hit Toyota showrooms in the coming months those figures figure to be just the start.