A number of technologies come together in both the Honda Insight and Toyota Prius to make them the amazingly clean and efficient cars that they are.

Low Aerodynamic drag - Features such as smooth underbody panels are an important part of improving efficiency.

Weight savings - Reducing weight reduces amount of energy needed to propel the car, and permits smaller, more efficient motors & batteries.

Hybrid powertrain - The most complex technology in the Insight & Prius, with remarkable similarities & differences.

Other energy saving and emissions reducing technologies - While body technologies and the hybrid powertrain lead to better efficiency and greenhouse gas emissions, it is largely gasoline engine and catalytic converter technologies that lead to lower levels of smog-forming emissions.

Which Car is More "Advanced?"

Neither. Each car contains significant advancements not found in the other.

The Insight has more advanced body construction technology (aluminum-alloy body reduces weight improving efficiency). The Insight has more advanced aerodynamic features. The Prius has a more advanced system for controlling fuel vapor emissions (bladder fuel tank).

In terms of gasoline engine, the cars are also very equal. The Insight's engine uses lean-burn technology (altered air-fuel ratio), while the Prius uses the Atkinson cycle (altered compression ratio). These are different engineering solutions both aimed at improving efficiency.

On the hybrid/electric side of the powertrain, the Prius uses a more complicated setup than the Insight. However, even with the Prius's two electric motor/generators vs. the Insight's one motor/generator, both cars are able to operate almost identically in terms of when and how the electric motor is used as opposed to the gasoline engine.

These differences ignore the fact that the Prius & Insight have a remarkable number of similarities, and both take a very similar strategy to combining hybrid electric technology with other technologies to create a "greener" car.

Perhaps at the end of the day, what really matters isn't how simple or advanced a car is, but what it delivers in terms of efficiency, emissions and other elements of performance.