View source for Walkability/New construction

If [[walkability]] is achieved by building brand-new neighborhoods, how long would it take to "break even" considering the carbon emissions of the construction & materials?

==Simplified model==
* consider the carbon footprint of making a new building, per person living there.
* assume a full extreme lifestyle change: people go from "USA average" amount of driving, to zero driving.
In such a case, it would take about 7-8 years to pay itself off:
<tab name="(see maths)">
{{dp
|<nowiki>building.construction_ghg_by_floor_area</nowiki>
|<nowiki>530.43 kg/m^2</nowiki>
|<nowiki>CO2 emissions involved in making a building, per unit of floor area</nowiki>
|<nowiki>Includes all materials and construction processes.</nowiki><br /><small>But probably doesn't include furnishings.</small><br /><nowiki>
</nowiki><br /><nowiki>
Source:</nowiki><br /><nowiki>
Case Study on Carbon Footprint Life-Cycle Assessment for Construction Delivery Stage in China</nowiki><br /><nowiki>
by Xiaojuan Li, Chen Wang, Mukhtar A. Kassem, Shu-Yi Wu, and Tai-Bing Wei</nowiki><br /><nowiki>
https://www.mdpi.com/2071-1050/14/9/5180</nowiki><br /><nowiki>
Sustainability 2022, 14(9), 5180; https://doi.org/10.3390/su14095180</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Quote: "...the area carbon-emission intensity is between 400 and 800 kgCO2/m^2, and the average area carbon emission of the building is 647.99 kgCO2/m^2 compared to other research results for emissions around 412.87 kgCO2/m^2"</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
So I decided to take the midpoint between both figures.</nowiki>
}}
{{dp
|<nowiki>gasoline.ghg_by_energy</nowiki>
|<nowiki>71.30 kg / million btu</nowiki>
|<nowiki>CO2 emissions of burning gasoline</nowiki>
|<nowiki>https://www.eia.gov/environment/emissions/co2_vol_mass.php</nowiki>
}}
{{dp
|<nowiki>average_us_vehicle.fuel_usage</nowiki>
|<nowiki>489 gallons gasoline/year</nowiki>
|<nowiki>The average American vehicle uses this much gasoline (measured in energy units)</nowiki>
|<nowiki>Top Numbers Driving America's Gasoline Demand</nowiki><br /><nowiki>
https://www.api.org/news-policy-and-issues/blog/2022/05/26/top-numbers-driving-americas-gasoline-demand</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Note: Since the statistic is mentioned specifically in relation to gasoline, we can '''probably''' assume that it excludes diesel-powered vehicles such as semi trucks. But the website doesn't specify that, so it's anyone's guess.</nowiki>
}}
{{dp
|<nowiki>usa.registered_vehicles</nowiki>
|<nowiki>275.9 million</nowiki>
|<nowiki>Number of registered vehicles in the USA</nowiki>
|<nowiki>Top Numbers Driving America's Gasoline Demand</nowiki><br /><nowiki>
https://www.api.org/news-policy-and-issues/blog/2022/05/26/top-numbers-driving-americas-gasoline-demand</nowiki>
}}
{{dp
|<nowiki>usa.population</nowiki>
|<nowiki>334416477 people</nowiki>
|<nowiki>Number of people living in the USA</nowiki>
|<nowiki>United States Population (Live) - Worldometer</nowiki><br /><nowiki>
www.worldometers.info › world-population › us-population</nowiki><br /><nowiki>
Last updated April 7 2022</nowiki>
}}
{{dp
|home_space
|400 square(feet) per person
}}
{{dp
|private_fraction_of_building
|70%
|Percent of the building's floorspace that is private living space
|The rest is hallways, stairwells, and common rooms.
}}
{{calc
|building.construction_ghg_by_floor_area * home_space / private_fraction_of_building
|years (average_us_vehicle.fuel_usage * gasoline.ghg_by_energy * usa.registered_vehicles / usa.population)
}}
</tab>

The real-life figure might be higher, because...
* can't really expect a full change to ''zero'' driving, just a lot less than before
* the calculation didn't include interior furnishings of the building, as far as I know
The real-life figure might be lower, because...
* the footprint of heating the new place{{x|i.e. an apartment or condo in a multi-unit residential building}} would probably be lower than the old place{{x|i.e. a single-detached suburban home}}
* less construction in other ways (especially road maintenance)

In any case, the carbon payoff of new construction could be worth it if there's no better option for [[Walkability/Existing housing]].

<!-- TALK: should i try to find a different case study that deals with per capita (or total emissions and total number of residents) instead of guesstimating floor space per person -->