What is the main characteristic of flexible pavement?

The main characteristic of flexible pavement lies in its design as a layered system that distributes loads applied by vehicles. This layering typically includes a surface layer made of asphalt, which is reinforced by additional layers beneath that might include granular materials, subbase, and the underlying soil or other foundation layer.

This layered structure allows flexible pavements to absorb and dissipate the stresses that result from vehicle loads. The flexibility of the materials enables the pavement to adapt to the moving loads without cracking, making it well-suited for varying traffic conditions and environmental factors. The ability to spread these loads over a wider area helps to prevent structural failure and prolongs the life of the pavement.

In contrast, other options focus on attributes not inherent to flexible pavements. While solid concrete bases are characteristic of rigid pavements, extensive drainage systems can be a consideration for any type of pavement but aren't a defining feature of flexible pavements specifically, and the material composition described in the fourth option suggests a limitation that does not reflect how flexible pavements can sometimes incorporate varying materials beyond just asphalt for optimal performance.