Open-Graded Friction Course

Open Graded Friction Course (OGFC) has been used since 1944 in the United States to improve the frictional resistance of asphalt pavements. An important safety feature of an open-graded asphalt surface is that it reduces the splash and spray that you would see with other types of pavement. These pavements are also frequently used to reduce road noise in urban areas. This is an advantage of asphalt pavements.

Asphalt Concrete

A high-quality, thoroughly controlled, engineered mixture made by heating asphalt cement and mixing it with aggregates and mineral fillers. Typical proportions are 94 to 96 percent aggregate and 4 to 6 percent asphalt cement.


In 1924, a group of engineers working at Bell Telephone Laboratories invented a measurement and a scale that would help the world quantify the measure of sound. The team devised a new unit of measure called the decibel (dB), named in honor of the laboratory’s founder and telecommunications pioneer Alexander Graham Bell. Later, the (A) was added to denote decibel levels to which the human ear is most sensitive.

Porous Asphalt

Porous asphalt pavement is a paved surface comprised of asphalt, gravel, and stone, formed to create a permeable surface. Stormwater which passes through the pavement may completely or partially infiltrate the underlying soil, the excess being collected and routed to an overflow facility through perforated underdrain pipes.

Sound Walls

A common, but less effective, road noise mitgation tool constructed along roads and highways to reduce road noise.


Noise is defined as “unwanted sound.” Like all other sounds, noise is a form of acoustic energy. An understanding of the physics of sound and how humans respond to it is required to understand noise.