Rather than shoulders, urban roads usually have raised edges called curbs, which provide a barrier between the street and the adjoining property or sidewalk. Traffic lights and signs help regulate the movement of vehicles along these roads and control the access to some roads. These designations are based on the amount of traffic each type is designed to carry. Most urban roads are residential, or local, roads that allow vehicles to access public and private property. These roads make up 70 percent of total urban-road mileage but handle only 14 percent of all urban traffic.
Collector roads convey traffic from residential roads to larger roads called arterials.
Arterials are used to get quickly from one point to another and can accommodate high volumes of traffic. In large cities, arterials are often similar to highways in construction even though they are located within city limits. Although arterials account for only 17 percent of the urban-road mileage, they account for most of the traffic in cities. Rural roads are also classified as local, collector, or arterial roads. Because of the light traffic and extensive mileage on these roads, design standards are relatively low.