Develop the access grid

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Spatial planning: Step 4

The access grid refers to the street layout that in turn determines permeability or the efficiency of movement in an area. The street layout by its very nature also determines block sizes and configurations that strongly affects land use potential, real estate dynamics, future adaptability, the cost of infrastructure provision and matters such as urban safety and environmental management. It is therefore the first critical step in the design of the urban structure.

Urban designers are generally faced with three types of scenarios when undertaking precinct planning and design:

In some precincts, a combination of the above scenarios may be evident.

Scenarion 1:
Brownfields development

In this scenario, it may be necessary to do infill development, redevelopment or a combination of both. The existing access grid must be reviewed in relation to the precinct vision, design objectives and the challenges and opportunities highlighted in the precinct status quo report. Some element of reconfiguration of streets and blocks may be necessary, depending on the alignment of the existing grid to the precinct vision and objectives.

Scenario 2:
Greenfields development

In this scenario, urban designers have the opportunity to develop the access grid in its totality, responding to the precinct vision, design objectives and site features such as topography, hydrology and key site features. Good design will always be site-responsive.

Scenario 3:
Informal development

In this scenario, informal development has taken place with little or no regard for street provision, future infrastructure or green space provision. Depending on factors such as the size of the informal settlement and the land on which it is situated and environmental constraints such as floodlines, in situ ugrading can be undertaken either through a ‘reblocking’ approach or through ‘re-layout’.

Assessing the current access grid

In a brownfields environment, the first step is to assess and classify the existing lay-out, and to assess its benefits and drawbacks in relation to the stated precinct vision and design objectives.

01

Conventional layouts

02

Fused grid lay-out

03

Land use distribution comparison between layout types

04

Informal development

Develop or optimise the access grid

The movement network selected for the urban hub should achieve the following objectives:

Allow permeability for a range of users;
The urban hub should be low-speed pedestrian-friendly environment, and pedestrian movement must be prioritised within the interchange zone;
The access grid must be site responsive and should;
- Ensure street orientation supportive of both connectivity and legibility
- Be aligned with desire lines to especially the interchange zone and other major attractions in the hub
- Be aligned to contours for more even travel paths
- Respond to major infrastructure installations
The access grid must be well-connected to both the metro grid and to surrounding neighbourhoods.

Rectangular blocks of 50 – 50 m wide and 150 – 200 m long have successfully worked in many cities globally under conditions of mixed land use, high density and public transportation.

Figure: Development of the access grid

In designing block lengths, it is necessary to consider land use and optimal stand sizes, the availability of land (more intersections are land consumptive) as well as ease of pedestrian movement. Ideally, longer street blocks should feature mid-block pedestrian throughways and midblock street crossings. The requirement for site-responsiveness inevitably results in some degree of grid warping.

Explore more on urban hub access and movement network design

Land use distribution	Traditional grid	Conventional loop and cul-de-sac	Fused grid
Residential	46.8	54.5	52.2
Commercial and institutional	6.6	3.8	6.6
Recreation and open space	12.1	10.1	12.1
Streets	31.7	28.8	26.4
Vacant land	2.7	2.7	2.7
Total land area	100	100	100