Urban Street Design: Principles, Paving, and Elements
Urban Street Design: Traffic Coexistence and Shared Spaces
Traffic Coexistence in Shared Streets: The movement of pedestrians, vehicles, bicycles, and buses often occurs on the same street, without strict differentiation between various modes of transport. In these shared streets, it is often challenging to allocate dedicated parking or pedestrian circulation space. Furthermore, bus movement can be difficult, and financial considerations are complex. These streets typically have a limited total section width, preventing the assignment of separate traffic lanes. There is also no single predominant traffic type, as their overall use is not excessively high.
Criteria for designing these streets prioritize the pedestrian experience within the road space. This is achieved by:
- Using differentiated materials and textures to distinguish areas.
- Incorporating traffic-calming elements and physical barriers to prevent unauthorized entry.
- Implementing clear signage for pedestrian protection and defining entrance points to buildings with bollards or other physical barriers.
- Utilizing gardens and street furniture to define environmental and traffic zones.
Intersection Design: Enhancing Safety and Mobility
Security and convenience for both pedestrians and drivers are paramount at intersections. Effective design ensures adequate mobility by categorizing intersections into three main types:
- Elementary Intersections: These are roads that intersect without any channeling elements. Traffic is governed by priority rules, with or without branching, and basic signage at crossings.
- Channelized Intersections: These feature small islands, roundabouts, or other elements to guide traffic flow. They are suitable for areas with large surface areas and high traffic volumes, or for intersections with more than four branches.
- Signalized Intersections: Traffic is regulated by traffic lights, typically used in areas with higher traffic movement. The goal is to facilitate the most natural movement possible, clearly and simply.
It is advisable not to overuse roundabouts; a few well-designed large roundabouts are often better than many small ones. Roundabouts should ideally be between 5 and 7 square meters. If smaller than 5 square meters, they should be clearly marked by road markings. Landscaped roundabouts typically range from 20 to 30 square meters. As a general rule, a roundabout solution can be chosen if traffic volumes are similar across all intersecting branches.
Street Paving: Materials and Design Considerations
The materials used for street paving depend on various parameters and the load levels they will support. This includes considering the sidewalk and underground services beneath the roadway (water, gas, electricity), as these often require opening trenches for repair and maintenance. The main characteristics of paving materials are categorized into three areas:
- Structural and Functional: This considers the pavement’s resistance to traffic loads, its behavior under various traffic conditions, its ability to resist external agents (weather, collisions), and its drainage function.
- Economic: Key economic factors include installation costs, speed and ease of construction, use of local materials, ease of cleaning, possibility of repair and replacement, accessibility for utility work (ease of opening and closing inlets), and overall durability.
- Formal and Aesthetic: This encompasses texture, color, paving patterns, level variations, and the overall aesthetic consideration for both the medium and long term.
Common Pavement Types in Urban Spaces:
- Concrete Pavements: Include mass concrete paving, poured concrete surfaces, and concrete pavers.
- Bituminous Pavements: Derived from petroleum products, these include bituminous mixtures and hot mix asphalt.
- Stone Pavements (Petreos): Examples include gravel surfaces, natural stone paving, and carved stone pavers.
- Hydraulic Pavements: These are made from cement mortars and concrete, such as continuous in-situ terrazzo, terrazzo tiles, or cement tiles.
- Ceramic Pavements: Derived from clay, examples include edge-set brick (e.g., Toledo style) and ceramic tiles.
Urban Limits and Complementary Elements
These elements define boundaries and complement the urban environment. They include:
- Curbs: Define the edge between the roadway and sidewalk.
- Basins and Fords: Depressions in the pavement, such as trenches or swales, designed to facilitate water drainage or pedestrian/vehicle movement across specific points.
- Grates and Covers: Surface elements that provide access to underground services and infrastructure (e.g., manhole covers, storm drain grates).
- Kilometer Markers: Used for distance indication along roads.