The thickness of an asphalt driveway depends on the expected load and usage. For most residential driveways in Chicago, a thickness of 2 to 3 inches of compacted asphalt is standard. For driveways with heavier traffic or vehicles, such as trucks or RVs, a thickness of 4 to 6 inches may be necessary. It's also important to have a properly prepared base, typically consisting of 4 to 8 inches of crushed gravel, to ensure the longevity and stability of the asphalt surface. Consulting with a professional contractor can help determine the appropriate thickness for your specific needs.