Urban Road Design Factors and Guidelines
Regulatory Factors
General Policies
Any decision regarding a specific project or urban road design must be consistent with existing urban transport legislation. The state, acting as a guardian of collective welfare, manifests this through laws based on essential factors of well-being.
Social Factors
Public Safety
This is the primary factor in any road design element. Citizen safety during activities involving public roads is paramount.
Environmental Continuity and Land Use
An urban environment possesses a degree of continuity, both functionally and spatially, which can be affected by road infrastructure.
Environmental Preservation
Environmental degradation and pollution impact the population’s well-being in ways that are difficult to quantify but undeniable.
Functional Factors
Pedestrians
Pedestrians, including those with disabilities and special equipment, are considered in road design. Walking is the most natural, accessible, and often economical mode of transport, but it also carries risks.
Passengers
Passengers utilize various vehicles, and their characteristics influence the design of road elements used for boarding and alighting buses and taxis.
Drivers
Drivers are central to motorized transit. Traffic conditions are closely related to their characteristics and psychological factors.
Cyclists
Cyclists use individual transport devices powered by human power, consisting of two aligned wheels. Road designs must accommodate their needs.
Operational Characteristics and Demand
Flow Intensity
The number of vehicles on a road depends on various factors. For new infrastructure, traffic generation models are used to predict flow, linking demand with socio-economic and urban economic variables.
Flow Composition
The size, weight, and mobility of different vehicle types vary significantly. The proportions of each type within traffic flows are also variable.
Speeds
Speed greatly influences demand, as citizens are sensitive to travel time variations. The benefits of road improvements are often measured in terms of time saved due to increased speed.
Road Markings
Classification
According to their shape:
- Longitudinal Lines: Delineate lanes, indicate no-passing zones, parking restrictions, and dedicated lanes.
- Transverse Lines: Indicate stopping points and pedestrian/bicycle crossings.
- Symbols and Legends: Guide and warn users, including arrows, yield triangles, and stop/slow signs.
- Other Boundaries: Unclassified markings not dominated by longitudinal, transverse, or symbolic components.
Depending on their height:
- Flat: Up to 6 mm high.
- High: More than 6 mm and up to 21 mm high, used to supplement flat markings. Increased visibility, especially in rain.
Elements higher than 21 mm, often called studs, can enhance delineation but may pose risks in certain situations.
Materials
Various materials exist with different costs, durability, and installation methods. Selection should consider health and environmental impacts, pavement type, and traffic flow.
- For Flat Boundaries: Paints, plastics, thermoplastics, preformed tapes.
- For Elevated Boundaries: Studs or “cat eyes” made of plastic, ceramic, or metal, with reflectorized surfaces.
Signal Location for Efficiency
Longitudinal Location
Ensures users can maintain the maximum allowed speed.
Lateral Location
Within the driver’s cone of attention (10° from the visual axis), not too far from the road, nor too high or low.
Height
Ensures visibility, considering obstacles like parked vehicles, vegetation, and road geometry.
Longitudinal Lines Classification
- Centerline markings
- Lane lines
- Road edge lines
- Other lines
Centerline Markings
- Broken Centerline: Permits overtaking where geometry allows.
- Double Continuous Centerline: Prohibits overtaking on two-way roads with reduced visibility.
- Mixed Centerline: One continuous line and one broken line.
Lane Lines
- Segmented Lane Lines: Ratio of marked section to gap varies with road speed.
- Continuous Lane Lines: Indicate no lane changes.
Lane Width
Specifies the width of travel lanes.
No-Passing Zones
Carefully defined based on specific criteria due to the high risk of overtaking maneuvers.
Table Usage
The table is used for “MEDIUM GENERATION OF JUNCTIONS AND RECENT MEANS OF EXPRESS TRANSPORT.” It provides values for E1, E2, L1, and L2 at a speed of 40 km/h, used in road design.