Thursday, October 21, 2010

A Brief Introduction to Pavement Design: A Fifteen Minute Writing Exercise

According to Southworth and Ben-Jospeh in Streets and the Shaping of Towns and Cities, roads, parking lots and other automobile related infrastructure count for 50% of land use in most U.S. cities. Roads date back to Roman times. Whereas the idea of engineered roads was introduced approximately 200 years ago. In the U.S., the majority of the roads have been built. Engineers are now focused on the management and maintenance of our already existing infrastructure.

Pavement is an engineered structure on the ground that facilitates the movement of goods and people. Pavement is implemented for all weather mobility for higher safety, efficiency and fuel economy. Pavement design can have a huge impact on the environment, energy consumption, connectivity, labor, maintenance, etc. There are many different types of pavement, some dirt roads are coated with one thin layer of pavement to increase fuel economy by reducing rolling resistance. Coating dirt also helps decrease dust and noise. Other pavements are very thick, like the deep pads used for rail road subsurface.

The pavement subsurface helps displace the load from vehicles or trains. The majority of the damage to roads comes from trucks. A truck traveling down the interstate is similar to the damage inflicted by 5,000-10,000 sport utility vehicles. Trucks are limited to 40,000 ton carrying capacity due to safety and stopping distance. More damage is done to the roads when trucks implement high tire pressure or have less tires to displace the load. However, there are trade offs. If trucks were able to carry 10% more weight, green house gas emissions would decrease due to efficiency.