Growing Roads

May 2010

Growing With You

May 30, 2010 11:13 PM
Pirijan Ketheswaran

Briefly: What are Growing Streets?

When a road is newly paved or redone, saplings are planted on top of a root guide at specific nodal flex points alongside a street. Then the pavement poured around these nodes and into the street is perforated in such a way that, over time, as the tree grows it's roots will be guided to push out and up and break the road surface along those perforations in a controlled way.

Breaking up the perforations will create a cobblestone effect that will act as a traffic calming measure to encourage pedestrian use around the same time desired walkable access to nearby activities and amenities are developed. Additionally, local grasses planted in the perforations along with the highly permeable nature of the system, act to effectively absorb excess storm-water to prevent runoff and overloading sewage systems.

The following three illustrations show, Generally, how this the Growing Road will mature with a neighbourhood:

Early Stage:

These newly created roads - with only un-seperated perforations - will initially act as smooth high flow roads to accommodate lower density and higher vehicle use.

In this example I've chosen to draw the perforations (the dashed lines) as concentric rings, but the actual pattern could be a something unique to each neighbourhood.

The Purple Lines are pedestrian sidewalks.

The Blue Line at the bottom is a bicycle lane or at least the space for one to be put in later as road use changes.
(-- both of these are paved normally)

The Diamonds represent the nodes where the saplings will be planted and grown.

  • and the dashed lines represent the perforations in the concrete that will be pushed apart at later stages.
  • So right now, the road is smooth and accommodating to high speed car transport

Mid Growth Stage of the Trees:

Over time, the typical single-detached suburban home typology is later complimented with slightly higher density buildings and mixed uses.

The trees (represented by the diamonds) have matured somewhat and their root systems have expanded to push out the first 2 to 3 concentric ring sections:

This gradually-occurring partial cobbling of the road will slightly slow traffic down to encourage pedestrianism as the area starts to make the transition to a more walkable neighborhood as nearby services and density are built.

Final Stage

the Final stage is very long term (depending on the tree species), and in that time the growing road neighbourhood has matured a lot in that time. In this case, it's got more a lot more density and social services (community centre) that encourage the reclamation of the streets by pedestrians more than ever.

Coinciding with this, the trees have grown to full size and their roots have spread under and pushed out all the perforations to create a meandering fully cobblestone road.

Additionally, the absorptive potential of the spaces between the plates at this stage is even higher than it initially was. The importance of groundwater reclamation will only increase as future weather conditions are increasingly affected by global climate change trends and local heat island effects.

Cross section of an Individual Node

The above image shoes an illustrated cross section of a node in the final stage.

  1. the tree itself
  2. the concentric perforated plates (colours correspond to earlier figures)
  3. the guided roots of the tree are pushed out by
  4. an inflexible root guide that pushes out the taproot growth pattern so that the farther plates get eventually pushed up too.

Use and Feasibility

It is envisioned that Growing Streets will be installed in new suburban neighbourhoods, as well as older established ones. Where the long-term intent is to gently transform a typical car-dependent suburban/residential neighbourhood typology into a higher value more pedestrian friendly, mixed-use community that is both of social/cultural and economical higher quality.

As seen in the above cross section, Growing Roads are a relatively low-tech design. However, any increased costs to developers can be recouped by the higher market value of residences. Higher property tax based on market value assessments, both in the short and (especially) long-term, are the incentive for municipalities.

Growing Roads have many Benefits

  • They give residents a sense of the future development of their community (towards intensification, mixed use and walkability).
  • The physical transformation of roads is a tangible reminder to both residents, government and development interests of the aspired goal of future neighbourhood development over time to create more walkable environments.
  • trees are apolitical. Tree species sets the timeline for development - and can't be backtracked or delayed by frequently changing political interests and councils.
  • permeable streets absorbs excess precipitation and helps avoid storm-water drainage overloading sewage systems flooding sludge into lakewater.

As well as Challenges

(Regrettably I'm no engineering expert so, or course, there are an inevitable few practical issues that need to worked out)

  • Issues of de-ice-ing, pot holes
  • Road longevity and dealing with weight and traffic volumes
  • Maintaining sitting and slope over time so that stormwater doesn't pool

Thanks for Viewing my Idea




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