exploring sidewalks: impact similar to housing..?

When constructing a building or a house, there is need for access to the building. The more wealthy a nation the more sophisticated the infrastructure will be . After dirt roads, a stabilized road is build, followed by a constructed road , and only much later, when a country really climbs the progress ladder, sidewalks and pedestrian walks are added. And only later, when a country is very rich, it will start adding bicycle networks, like Denmark and the Netherlands.
So its interesting to have some idea of the roads and sidewalks impacts , besides the building impacts. Especially when a neighborhood is evaluated, both should be included. No houses without infrastructure, planned or unplanned . As we found out in a our “Urban Harvest research” for a local district, [1] one of the most interesting options to create a “ 0-impact built environment” on neighborhood level was to free land and save on maintenance by taking out half of the roads, and make these one way roads. : it provides more productive land, reduces maintenance and provides in-system materials for other more crucial construction works, necessary to keep a 0-impact neighborhood option alive.(producing its own materials , to have Embodied land limited to what is available as land in the area).
When looking at individual buildings , part of sidewalks and roads should be included in the impact from the function provided. We need data to see how relevant this is compared to the building impact. It could be significant , since I noticed that many countries construct sidewalks with tiles in solid concrete foundations . Which by the way seems a weird and material wasting way of doing. Below a small investigation providing some basic data as a start.

different ways of making sidewalkssidewalks

The Netherlands:
If we address only roads on municipal level , and assume half of these have sidewalks, on both sides (low estimate) , and assume these are average 1 meter wide (low estimate), in that case The Netherlands has 121000 km1 of sidewalk ( as much as length of roads) of 1 meter wide, which makes a total of 121,3 km2 of sidewalk.
The Netherlands has 17 million inhabitants, makes 7,5 m1 ( average ) or 7,5 m2 (1 mtr wide) of sidewalk per capita. Or 18 m2 per household unit ( 7 million housing units in NL). (of course, multifamily houses require less per unit or capita, and detached houses more.)
Globally
The table below , (with estimates based on public available stats on roads and sidewalks) shows similar data for other countries and continents, with however some significant differences.
Sidewalks per capita go from 0,8 m2 to 15 m2 in Australia. I already noticed when in Australia that they like to steer things along planned path’s … But 15 is even double from the Netherlands…! By the way: for a first estimated impression , its assumed for all countries and continents that half the (local) roads have sidewalks on both sides. Which of course is for discussion ( and research).

sidewalks tabel

Next question is: how is a sidewalk constructed? In the Netherlands a sidewalk is made of a sand bed and loose laid concrete tiles, of about 5 cm thick and 30×30 cm in size. Which is easy to open and close for small roads works, with easy recyclable tiles and sand. For most other countries I noticed during visits , the construction is different, usually some of big or small tiles or cobble stones laid in a concrete foundation. Which creates significantly impacts, as we will see.
Suppose 50% of all roads worldwide have sidewalks ( 2 sides) and 50% of these are made of concrete beds and finishings. And are 1 meter wide.
That is globally 13 million km1 sidewalk in concrete ,or 13 billion m2 sidewalks in concrete. (~ 2m2 per capita). I made an educated guess this is a 15 cm concrete bed and 5 cm cement layer to hold the finishing tiles. ( which is a low estimate ), this gives 2,6 billion m3 of concrete ( or ~ 0,37 m3 /capita )
if replaced every 20 years, its 130 million m3 (286 million tonnes)/year, which is about 1,5 % of total yearly global production of concrete (20 billion tonnes). The embodied energy at 0,75 MJ/kg , comes down to 214 billion MJ and the CO2 emissions at 0,1 kg CO2/kg leads to 28 billion kg, or 28 megaton.
residential areas
Now these are some first impressions based on rough data and country wide averages. If we look at residential areas in more detail, things are a bit different . Some real research has been done by Deilmann in the city of Dresden, and he estimates that in the residential areas it comes down to 1 m2 of sidewalk per m2 of housing-floor. [2] This implies that we have as much space reserved for our houses as for walking outdoors. So for every m2 house, in any evaluation tool or LCA of a house an equal amount of sidewalks should be added to the equation!
And what about the impact? An average house in the Netherlands weighs 1000 kg/m2 . If I compare this to a m2 of sidewalk of the concrete bed type, this weighs 0,2 m3 of concrete, or 0,2x 2400 kg/m3 is 480 kg , about half. However we are now constructing timber-frame and biobased houses at around 500 kg/m2 floor. Which would bring this to same level of resource consumption! By mass weight that is. Next step is of course the Embodied energy impact of that mass: which will be higher for concrete as for timber-frame houses, and subsequently for sidewalks: Sidewalks have -possibly- more impact as housing…! A more in depth analyses is required, (for instance with the MAXergy approach [3]) , and with more reliable data of course. But the data so far suggest that this is an immense burden to our societies!

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References:
1 Urban Harvest + , a 0-impact built environment evaluation methodology, pilot case study general description see http://www.maxergy.org/urban-scale/
2 Deilmann, Clemens; Gruhler, Karin; Hennersdorf, Jörg, One m² infrastructure for one m² floor space?! in: Sruma, V.; Srumova, Z. (Eds.) : CESB 07 PRAGUE – Conference Central Europe towards Sustainable Building. Proceedings. Volume 1. Prague : Czech Sustainable Building Society, 2007, S.158-163
3 MAXergy, A exergy based methodology , including a closing cycles calculation tool. see www.maxergy.org

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