Voronoi City – Beyond the 4 sided Grid

 

We tend to consider the orthoganal 4 sided grid to be the ubiquitous city form, indeed other forms ares rearely considered when planning large areas.

But it wasnt always this way.  I would advise anyone interested in City Planning to read a classic review article – Hexagonal Planning in Theory and Practice Ben Joseph and Gordon Journal Urban Design No.3 2000.

Between 1900 and 1934 there were a number of proposed residential street pattern designs based on hexagonal forms by well known planner such as Charles Lamb, Noulon Cauchon and Barry Parker. Despite the theoretical advantages of this form they lost favour with the official approval, in the United States, of the Radburn layout based on loops and culs-de-sac.

The savings of time travelled through the diagonal streets in hexagonal layouts were stressed by Charles Lamb. He also stressed how this enables the even growth of a city from a single place through the creation of long European styles boulevards.

These ideas influenced a number of classic city plans at the beginning of the 20th Century such as those for Canberra and New Dehli, as well as plans for Hampstead Garden City, and part of Withenshaw.

There are other advantages, as the most efficient pattern for covering a surface hexagonal layouts can save around 10% in infrastructure costs, including a 10% reduction in road per house. Also three way intersections have improved sight lines and fewer collision points than 4 way crossroads. With feeder roads they can avoid the need for stop lines although this is not recommended in mixed traffic areas with pedestrians.

Cauchon also pointed out that if a hexagonal grid was pointed north then no building would be entirely north facing and all buildings would receive some sunlight throughout the day.

Hexagonal Planning was dealt a blow in the 1932 Presidential commission on housing where Thomas Adams favoured the Radburn type layout off a grid.  The main concern being the awkward shaped lots created in hexagonal layouts, though the advantages of hexagonal layouts when planning at a city scale were acknowledged.  Adams also distorted the evidence, adding extra units his own favoured layouts to make it appear the per unit cost was lower.  The ease of metres and bounds orthogoonal subdivision, and layouts based on the set-square, easier to design on corner lots,  also meant that these triumphed.

Today, as alternatives to conventional loop and culs-de-sac layouts are sought by planners the advantages might not seem so great.  Radburn layouts have fallen out of favour and in higher density schemes on an orthogonal grid corner units might not have a garden at all, whereas on hexagonal layouts it is possible for all units on a block to have gardens the same size.  Computer design also makes none set square planning much easier.

This study is an attempt to mesh some of the advantages of hexagonal and orthogonal layouts.

The accessibility advantages of hexagonal layouts at a city and town ship scale, in terms of infrastructure and accessibility is the starting point.  Although as you step down in scale and also deal with issues of existing landforms etc. it is necessary to distort layouts and introduce gridded and leaf like street patterns.

As soon as you distort a hexagonal grid you get what is known as a ‘voronoi’ pattern.  This is a pattern of all points closet to a specific point of interest.  As the grid is distorted it is not possible to have all cells being six sided, some could be 5, 4 or three sided.  This provides a palette of geometrical forms.  These points of interest could be open spaces, community facilities or transit stops.  If each cell were hypothesised as having the same population then higher density cells would be smaller, focussed on accessible places and corridors, with larger cells between.  The voronoi principle can be adopted at different spatial scales ensuring that all places on the plan are a maximum distance from different facilities such as fire stations, clinics, schools and shops.  

Connector street patterns would connect the points of interest, necessarily splitting hexagaons into quadrilaterals, a distorted grid.  This enables the advantages of the distorted grid, as for example set out by Paul Murrain, to be combined with that of the ‘meta grid’ of hexagons that organises neighbourhood scale.  

Between main roads that radiate out from a city centre or first ring roads the neighbourhood hexagons would create focal points for neighbourhood facilities such as local schools and shops away from heavily trafficked through routes.  

The following drawings illustrate how this concept might be realised on a 800m diameter hexagonal grid, showing how a variety of medium-low density housing forms can be accommodated, including perimeter blocks, with a variety of parking forms including parking lanes, courtyard parking and parking squares.

It illustrates that a more organic layout emerges, similar to the way in which traditional settlements enlarge over time, with a greater variety of views, and a more legible layout where it is easier to find your way towards points of interest.

Also because open spaces are more accessible and have a greater proportion of houses overlooking it a slightly smaller proportion of open space can be used to the same effect.  

The majority of junctions are three way, but on the main arteries strategically placed cross-roads are used with the express purpose of forcing traffic to stop and slow down, using the principles of ‘design by negotiation’ to avoid signalised junctions.

Culs-de-sac are only used to access the central parts of blocks that might not otherwise be accessible.

 

 

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