Function of Roadway System for Urban Areas
Urban areas are associated with cities and towns. AASHTO refers to suburban areas as the area surrounding an urban center, which are usually residential areas on the outskirts of a large city or town. Suburban areas may contain company facilities and industrial parks, but are primarily filled with housing and associated retail businesses. Note: In Abu Dhabi the term “suburban” is not used in its planning and design documents. Consequently, this Manual does not provide design criteria for suburban areas.
The functional classification of urban roads and streets is usually less clear than that of rural roads, as urban roads and streets generally are flanked by dense development that requires frequent access at the boundary of the road. Historical requirements for curb side parking and other uses (e.g. public transport routes or bicycle routes) further complicate functional definitions.
Most urban arterial roads continue to function as major through traffic routes, but the management of these roads often requires space to be dedicated to public transport or bicycle use in preference to private car travel. There is also a trend on outer urban roads for speed limits to be lowered to address pedestrian safety issues while sections of inner city streets (formerly through arterial routes) are sometimes converted to pedestrian areas or shared zones.
Consequently, the function of particular sections of road may change over time in accordance with community values. To better define urban roads and streets based on context sensitive street design, the Abu Dhabi Urban Planning Council defines urban streets with a two name convention as described in Section 2.4.4. The first name is the context name, based on the land use context, and the second is the street family name, based on the transport capacity.
Urban functional classifications are defined as follows:
1. Principal arterial system.
In general, the urban principal arterial system carries the highest traffic volumes and accommodates the greatest trip lengths. The following are the main characteristics for streets and roads of the urban principal arterial system:
- serves the major traffic movements within urbanised areas connecting central business districts, outlying residential areas, major intercity communities and major urban centres;
- serves a major portion of the trips entering and leaving the urban area, as well as the majority of the through traffic desiring to bypass the city; and provides continuity for all rural arterials that intercept the urban area.
The principal arterial system is segregated as follows:
a. Freeways and expressways.
Freeways and expressways may be connecting links in the urban area, and they may be extensions of rural or other principle arterials. These routes may traverse the urban area from one boundary to another or may simply connect to another connecting link. Also, freeways and expressways may provide access to circumferential routes around the city or provide links to the central city.
b. Other principal arterials.
These routes consist of a connected urban network of continuous routes having the following designations and characteristics:
- provide service to, through or around urban areas from rural arterial routes, and may be connecting links;
- serve generally as an extension of a rural arterial road;
- typically the access is controlled by regulation; and
- provide for an integrated network serving the entire urban area.
2. Minor arterials.
Minor arterials include all arterials not classified as principal arterials.
These routes have the following general characteristics:
- place more emphasis on land access than principal arterials;
- provide service for trips of moderate length and at a somewhat lower level of mobility than urban principal arterial routes;
- provides access to geographic areas smaller than those served by the higher system; and
- provides intra-community continuity, but will not, for example, penetrate neighbourhoods.
3. Collector streets.
In urban areas, collector streets serve as intermediate links between the arterial system and points of origin and destination. These facilities typically have the following characteristics:
- provide both access and traffic circulation within residential neighbourhoods and commercial/industrial areas, and
- may penetrate residential neighbourhoods or commercial/industrial areas to collect and distribute trips to and from the arterial system.
4. Local streets.
The streets functionally classified as urban local streets generally have the following characteristics:
- constitutes the urban streets not designated as part of a higher classification;
- serves primarily to provide direct access to abutting land and higher order systems;
- offers the lowest level of mobility and highest land access services; and
- discourages through traffic movements.
Provides typical percentages of urban functional classifications.