Why is the Audi A2 considered a pioneering car?

I've heard that the Audi A2 has been lauded for its innovative design and features, but can you explain exactly what makes it stand out?

The Audi A2 was one of the first cars to utilize an all-aluminum construction, making it significantly lighter than its competitors. This not only improved performance, but also made the car more fuel-efficient.

The A2 also featured a highly aerodynamic design, with a drag coefficient of just 0.25. This not only reduced wind noise and improved handling, but also contributed to its impressive fuel economy.