The type of pavement is dependent on the number, weight and speed of vehicles expected. Obviously, the more load expected on the pavement, the stronger the pavement section must be. Typically, the pavement section consists of several parts: existing base, subgrade, pavement, pavement surface, and drainage features. The existing base is the native earth material that is either cut or carefully compacted into place to form the general shape of the roadway. It is hoped that the existing base can carry most of loading placed on the pavement. The subgrade is a modified soil, asphalt or concrete layer above the existing base used to make up for bearing deficiencies in the existing base and to provide a relatively smooth surface for the pavement. The pavement is a protective topping for the subgrade and existing base to prevent erosion and saturation by water (since most earthen materials will eventually break down in the presence of water). In many cases, the pavement also provides some loading support. The pavement surface is designed to facilitate vehicle movement by minimizing friction but still providing sufficient friction for vehicle tire stability. If the pavement is the "roof for the pavement section, then the ditches, gutters and storm sewer system are the gutter system necessary to carry the drainage water away from the roadway where it cannot cause problems.
Existing base materials are any native material, with rocky material generally being the most stable and clay materials being the least stable. Subgrade materials usually consist of crushed limestone, lime or cement treated natural materials, asphaltic concrete or other load spreading materials. The pavement generally consists of reinforced concrete, hot mixed asphalt concrete, or penetration asphalt pavement. Depending on existing base materials, thicker sections may be required.
In general, streets experiencing high traffic volumes or heavy trucks shall be made of reinforced concrete and be curb and guttered. Other nonresidential streets can be either reinforced concrete or hot mix asphalt. Major and minor residential streets shall be hot mixed asphalt when street is curbed but may be two-course penetration pavement when streets are not curbed.
The City Engineer shall approve all street designs. The designer shall submit geotechnical data with the design to validate the sections proposed. The following is a table of minimum designs. Designs less than these minimums will not be considered.
Roadway Class | Minimum Wheel Loading (lbs.) | Minimum Asphalt Section | Minimum Reinforced Concrete Section |
Major City Thoroughfare | 18,000 | 2" Class D HMAC 8" Class B HMAC 6" Treated & Compacted Subgrade | 8" - Class "C" RC 6" - Treated & Compacted Subgrade |
Normal City Thoroughfare | 18,000 | 1.5" Class D HMAC 6.5" Class B HMAC 6" Treated & Compacted Subgrade | 8" - Class "C" RC 6" - Treated & Compacted Subgrade |
Arterial | 18,000 | 1.5" Class D HMAC 6.5" Class B HMAC 6" Treated & Compacted Subgrade | 8" - Class "C" RC 6" - Treated & Compacted Subgrade |
Collector | 9,000 | 1.5" Class D HMAC 6.5" Class B HMAC 6" Treated & Compacted Subgrade | 8" - Class "C" RC 6" - Treated & Compacted Subgrade |
Major Residential | 5,000 | 1.5" Class D HMAC 8" Treated & Compacted Subgrade | 6" Class "C" RC 6" - Treated & Compacted Subgrade |
Minor Residential | 5,000 | 1.5" Class D HMAC 8" Treated & Compacted Subgrade | 6" Class "C" RC 6" - Treated & Compacted Subgrade |