The standard for road asphalt thickness is not fixed but is determined comprehensively based on factors such as road grade, traffic load, material type, and design specifications. The following content will systematically introduce the asphalt thickness requirements in different scenarios.
General Thickness Range
In conventional design, the total thickness of the asphalt concrete surface layer is usually 15 to 20 centimeters. This range applies to most ordinary highways, but the specific value needs to be adjusted according to the actual project.

Classification by Road Grade
The asphalt layer thickness varies significantly between different highway grades, mainly based on traffic volume and usage requirements:
Expressways and Class I Highways: The asphalt layer thickness is generally 120 to 180 millimeters (12 to 18 centimeters), using a double or triple layer structure to withstand heavy traffic.
Class II Highways: The asphalt layer thickness should preferably be 60 to 120 millimeters (6 to 12 centimeters), with a relatively simplified structural design.
Class III Highways: The thickness is usually 30 to 50 millimeters (3 to 5 centimeters), and can be constructed using the mixing method; if a layered surface treatment method is used, the thickness can be reduced to 15 to 30 millimeters.
Class IV highways and rural roads: Thickness requirements are lower, generally 10 to 30 mm. For example, the asphalt concrete pavement thickness of some rural roads is not less than 6 cm (60 mm).
Structural Layer Thickness Subdivision: Asphalt pavements are often divided into multiple layers, each with a thickness designed according to its function.
Top Layer (e.g., AC-13): Approximately 4 cm thick, directly bearing wheel wear, requiring good skid resistance and smoothness.
Intermediate Layer (e.g., AC-20): 5 to 6 cm thick, primarily responsible for load transfer and waterproofing.
Bottom Layer (e.g., AC-25): 6 to 8 cm thick, serving as a transition layer between the base layer and the top layer, enhancing overall structural stability.
Base Layer and Subbase Layer: Typically using materials such as cement-stabilized crushed stone, the base layer thickness is approximately 20 cm, and the subbase layer thickness is determined by design (generally not less than 15 cm).