Classification of Urban Highways and Streets: Hierarchy and Network Planning
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A city's system of arterial roads, streets, and squares resolves a combined set of planning, technical, and aesthetic tasks that shape both the appearance and the daily functioning of the city. The primary tasks it addresses are:
- providing the shortest and most convenient routes for urban traffic and pedestrians between the city's different functional zones and within them;
- organizing surface runoff and the removal of stormwater;
- accommodating engineering networks and utilities;
- ensuring adequate ventilation or protection from winds;
- establishing the architectural and spatial composition of the city and creating compositional axes.
Why is movement one of the central functions of a city?
Movement ranks among the most important functions of the modern city, and today it is standard practice to separate vehicular traffic from pedestrian traffic within the urban environment. Mass movements of population and goods are carried out by urban transport, while pedestrian routes are treated as a distinct system.
The degree of population mobility and the intensity of transport loading depend on the size of the city, its functional profile, and its planning structure. Reducing the time residents spend travelling to a minimum is the core task facing urban planners.
Under current standards, in the largest and major cities the total travel time from place of residence to place of work should not exceed 40 minutes one way, and in all other populated places it should not exceed 30 minutes.
What types of transport serve modern cities?
Modern cities rely on several kinds of public street transport: the tram, trolleybus, bus, and taxi. In the largest cities the metro (underground railway) takes on great importance. For the cities of the future, promising modes include monorail lines, conveyors, and moving pavements.
Contemporary town planning strives for a high level of equipment and refinement of urban communication routes — arterial roads and streets. Convenient service of the population by urban transport, a sufficiently high travel speed, safety, and economy can all be achieved only when streets are strictly differentiated by purpose and by the types of traffic they carry (Fig. 1).
How are city streets classified?
Current standards for the design of cities divide all streets of populated places into classes according to their function and traffic role:
- I — high-speed roads;
- II — arterial roads of citywide and district significance;
- III — roads of local significance: streets of residential, industrial, and warehouse districts, and driveways;
- IV — pedestrian roads.
Figure 2 presents a modern typology of streets and squares.
What are arterial streets and how do they differ?
Arterial streets carry the main flow of mass urban transport and are divided into citywide and district categories. The citywide arterials are further split into:
- a) roads of continuous traffic, which provide transport links between residential and industrial districts, with intersections at other streets on different levels;
- b) roads of regulated traffic, which provide transport links within the city between residential districts and the public centre, with intersections at other streets on the same level.
The design travel speed on arterial roads is 60–80 km/h, depending on the size of the city and the conditions of the urban-planning situation. District-level arterials provide transport connections within a district as well as with citywide arterials; their intersections with other streets are made at a single level, and the design travel speed is up to 80 km/h.
How are local streets and roads subdivided?
Streets and roads of local significance are subdivided according to the movement they serve:
- residential streets, which provide vehicular and pedestrian links between residential districts and micro-districts and the arterial streets, with a design travel speed up to 60 km/h;
- roads of industrial and utility-warehouse districts, intended for hauling materials and goods and connecting to freight-traffic roads, with a design travel speed up to 60 km/h;
- pedestrian streets and roads, intended for pedestrian links with workplaces, institutions, service enterprises, recreation areas, and public transport stops;
- settlement streets, which serve transport links within the residential zone toward the public centre and the institutions and service enterprises of the settlements, with a design travel speed up to 30 km/h;
- driveways, intended for transport links within micro-districts, with a design travel speed up to 30 km/h.
What is the cross-sectional profile of a street?
Establishing the cross-sectional profile is an important planning factor in the design of streets. The cross-sectional profile of a street is a cut taken at its most characteristic point, where the principal elements are visible — the carriageway, the pavements (sidewalks), and the strips of greenery.
The cross-sectional profile is set according to the size of the city, the estimated intensity of movement of all types of urban transport and of pedestrians, the prevailing number of storeys of the surrounding development, terrain conditions, methods of draining surface water, and the placement of underground utilities.
The width of the carriageway is determined with regard to the intensity of the traffic flow and its composition. The width of a single traffic lane is taken as 3.5–3.75 m depending on the dimensions of the vehicles. The minimum number of lanes for arterials is 4, and for streets of local significance 1 (or 2).
On arterials with heavy traffic (about 1000 vehicles per hour) a local service carriageway is designed. On citywide arterials a dividing strip (up to 6 m wide) is provided along the axis and is set aside for landscaping.
How are pavements and dividing strips arranged?
The pavement is separated from the carriageway by a dividing strip with plantings. The width of the pavement is taken as a multiple of a single pedestrian movement lane (0.75 m) and must be no less than 4.5 m. Near public buildings the width of pavements reaches 6–9 m or more.
In the profile of residential streets, the correct placement of dividing strips set aside for plantings is of great importance. The plantings in these strips are intended to protect pedestrians from the adverse effects of exhaust gases and dust. The overall width of the street is defined within the red lines.
What is the red line of a street?
The red line is the outer boundary of the street on the pavement side, facing the built-up frontage. Between the red line and the development a setback is established — no less than 6 m on arterials and no less than 3 m on streets of local significance.
