Editing IPCC:AR6/WGIII/Chapter-8 (section)

==== 8.4.2.2 Co-located Housing and Jobs, Mixed Land Use, and High Street Connectivity ====

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Integrated spatial planning, co-location of higher residential and job densities, and systemic approaches are widely identified with development that is characterised by the 5Ds of transit-oriented development (TOD) based on density, diversity (mixed land uses), design (street connectivity), destination accessibility, and distance to transit. Spatial strategies that integrate the 5Ds are shown to reduce VMT/VKT, and thereby transport-related GHG emissions through energy savings. The effect of urban form and built environment strategies on VMT per capita varies by a number of factors ( [[#Ewing--2010|Ewing and Cervero 2010]] ; [[#Stevens--2017|Stevens 2017]] ; [[#Blanco--2018|Blanco and Wikstrom 2018]] ). Density and destination accessibility have the highest elasticities, followed by design ( [[#Stevens--2017|Stevens 2017]] ). Population-weighted densities for 121 metropolitan areas have further found that the concentration of population and jobs along mass transit corridors decreases VMT/VKT significantly when compared to more dispersed metropolitan areas. In this sample, elasticity rates were twice as high for dense metropolitan areas located along mass transit lines ( [[#Lee--2020|Lee and Lee 2020]] ).

Meta-analyses of the reduction in VMT and the resulting GHG emissions consider the existing and still dominant use of emitting transportation technology, transportation fleets, and urban form characteristics. Varied historical legacies of transportation and the built environment, which can be utilised to develop more sustainable cities ( [[#Newman--2016|Newman et al. 2016]] , 2017), are often not taken into account directly. Metropolitan policies and spatial planning, as evident in Copenhagen’s Finger Plan, as well as strategic spatial planning in Stockholm and Seoul, have been major tools to restructure urban regions and energy patterns ( [[#Sung--2017|Sung and Choi 2017]] ). Road prices and congestion charges can provide the conditions for urban inhabitants to shift mobility demands and reduce vehicle use ( [[IPCC:Wg3:Chapter:Chapter-5#5.6.2|Section 5.6.2]] ). Surprisingly, even cities with higher population densities and a greater range of land uses can show declines in these important attributes, which can lead to emissions increases, such as found in a study of 323 East and South East Asian cities ( [[#Chen--2020c|Chen et al. 2020c]] ). Conversely, the annual CO 2 emissions reduction of passenger cars in compact versus dispersed urban form scenarios can include at least a 10% reduction by 2030 ( [[#Matsuhashi--2016|Matsuhashi and Ariga 2016]] ). When combined with advances in transport technology, this share increases to 64–70% in 2050 based on compact urban form scenarios for 1727 municipalities ( [[#Kii--2020|Kii 2020]] ).

As a reaffirmation of AR5, population density reduces emissions per capita in the transport, building, and energy sectors ( [[#Baur--2015|Baur et al. 2015]] ; [[#Gudipudi--2016|Gudipudi et al. 2016]] ; [[#Wang--2017|Wang et al. 2017]] ; [[#Yi--2017|Yi et al. 2017]] ) (see also Sections 8.3.1 and 8.3.4 on past trends and forecasts of urban population density and land expansion). Urban compactness tends to reduce emissions per capita in the transport sector, especially for commuting ( [[#Matsuhashi--2016|Matsuhashi and Ariga 2016]] ; [[#Lee--2018|Lee and Lim 2018]] ; [[#Lee--2020|Lee and Lee 2020]] ). The relative accessibility of neighbourhoods to the rest of the region, in addition to the density of individual neighbourhoods, is important ( [[#Ewing--2018|Ewing et al. 2018]] ). Creating higher residential and employment densities, developing smaller block sizes, and increasing housing opportunities in an employment area can significantly reduce household car ownership and car driving, and increase the share of transit, walk, and bicycle commuting ( [[#Ding--2018|Ding et al. 2018]] ). In addition to population density, land-use mix, rail transit accessibility, and street design reduce emissions from transport ( [[#Dou--2016|Dou et al. 2016]] ; [[#Cao--2017|Cao and Yang 2017]] ; [[#Choi--2018|Choi 2018]] ). The impact of population density and urban compactness on emissions per capita in the household or energy sector is also associated with socioeconomic characteristics or lifestyle preferences ( [[#Baiocchi--2015|Baiocchi et al. 2015]] ; [[#Miao--2017|Miao 2017]] ). Changes in the attributes of urban form and spatial structure have influences on overall energy demand across spatial scales, particularly street, block, neighbourhood, and city scales, as well as across the building (housing) and transport (mobility) sectors ( [[#Silva--2017|Silva et al. 2017]] ). Understanding the existing trade-offs (or synergetic links) between urban form variables across major emissions source sectors, and how they impact the size of energy flows within the urban system, is key to prioritising action for energy-efficient spatial planning strategies, which are likely to vary across urban areas.

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