Road - INTRODUCTION
TYPES OF ROADS
Highways
Urban Streets
Rural Roads
ROADWAY ENGINEERING
Roadbed
Base Course
Wearing Course
Bituminous Pavement
Concrete Pavement
ROAD PLANNING AND ADMINISTRATION
HISTORY OF ROAD CONSTRUCTION


AUTOMOBILE
AUTOMOBILE INDUSTRY
PUBLIC TRANSPORTATION
TRUCK


Highways


Highways | High-Speed Roads | Types of Highways | Highways Access Control

Highways are high-speed roads designed to connect major cities. There are many different types of highways. Highways differ primarily in the amount of access control they have and, therefore, in the amount of traffic they are designed to carry. (Highways, High-Speed Roads, Types of Highways, Highways Access Control)




Highways

A complex freeway interchange near Los Angeles, California, shows a typical cloverleaf pattern that facilitates easy and safe route changing. Interstate freeways have limited access and maintain low gradient, straight routings for maximum long-range visibility and safety. (Highways, High-Speed Roads, Types of Highways, Highways Access Control)

Highways with fully controlled access can handle the most traffic and are built to the highest construction standards. Interstate highways, freeways, and expressways are examples of fully controlled-access highways. Vehicles that enter or exit these types of highways can do so only at certain points along the highway, generally by using special entrance and exit ramps. The ramps allow vehicles to access the road without disturbing the flow of traffic. Incoming vehicles must merge with flowing traffic, and vehicles leaving the highway use exit ramps that guide them off the highway without blocking the traffic behind. Intersections with other roads are avoided by using either bridges known as overpasses to carry one roadway over another or short tunnel-like structures called underpasses to carry one roadway under another. Finished strips called shoulders on the edges of highways allow drivers of disabled vehicles to make repairs or await assistance without blocking traffic. (Highways, High-Speed Roads, Types of Highways, Highways Access Control)

Highways with fully controlled access generally have two or more lanes for each direction of travel and often include medians (dividers in the middle of the road) to separate traffic moving in opposite directions. In Europe, highways with fully controlled access are called motorways, motor-routes, or autobahns. (Highways, High-Speed Roads, Types of Highways, Highways Access Control)

Some highways offer only partial control of access. These types of highways handle less traffic than do highways with fully controlled access. Highways with partially controlled access may intersect other roads at the same level (called at-grade), rather than using overpasses or underpasses. Vehicles can enter highways with partially controlled access at intersections rather than using ramps. However, the right-of-way is often given to one direction of travel, rather than requiring all traffic to stop at the intersection (see Traffic Control). Giving the right-of-way to one direction of traffic helps keep traffic moving at higher speeds, although typically not at speeds as high as those on a highway with fully controlled access. One benefit of highways with partially controlled access is that they are much cheaper to construct than highways with fully controlled access. Many U.S. and state highways are roads with partially controlled access. (Highways, High-Speed Roads, Types of Highways, Highways Access Control)

Highways | High-Speed Roads | Types of Highways | Highways Access Control