Editing IPCC:AR6/WGIII/Chapter-10 (section)

=== Box 10.3 | Vehicle Size Trends and Implications on the Fuel Efficiency of LDVs ===

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'''Vehicle size trends.''' On a global scale, SUV sales have been constantly growing in the last decade, with 39% of the vehicles sold in 2018 being SUVs ( [[#IEA--2019d|IEA 2019d]] ). If the trend towards increasing vehicle size and engine power continues, it may result in higher overall emissions from the LDV fleet (relative to smaller vehicles with the same powertrain technology). The magnitude of the influence vehicle mass has on fuel efficiency varies with the powertrain, which have different efficiencies. Box 10.3 Figure 1 highlights this relationship using data from the same literature used to create Figure 10.4. Higher powertrain efficiency results in lower energy losses in operation, and thus requires less energy input to move a given mass than a powertrain of lower efficiency. This pattern is illustrated by the more gradual slope of BEVs in Box 10.3 Figure 1. The trend towards bigger and heavier vehicles, with consequently higher use phase emissions, can be somewhat offset by improvements in powertrain design, fuel efficiency, lightweighting, and aerodynamics ( [[#Gargoloff--2018|Gargoloff et al. 2018]] ; Wolfram et al. 2020). The potential improvements provided by these strategies are case specific and not thoroughly evaluated in the literature, either individually or as a combination of multiple strategies.

'''Lightweighting.''' There is an increasing use of advanced materials such as high-strength steel, aluminium, carbon fibre, and polymer composites for vehicle lightweighting ( [[#Hottle--2017|Hottle et al. 2017]] ). These materials reduce the mass of the vehicle and thereby also reduce the fuel or energy required to drive. Lightweighted components often have higher production emissions than the components they replace due to the advanced materials used ( [[#Kim--2016|Kim and Wallington 2016]] ). Despite these higher production emissions, some studies suggest that the reduced fuel consumption over the lifetime of the lightweighted vehicle may provide a net mitigation effect in comparison to a non-lightweighted vehicle ( [[#Kim--2013|Kim and Wallington 2013]] ; [[#Hottle--2017|Hottle et al. 2017]] ; [[#Milovanoff--2019|Milovanoff et al. 2019]] ; [[#Upadhyayula--2019|Upadhyayula et al. 2019]] ; Wolfram et al. 2020). However, multiple recent publications have found that in some cases, depending on, for example, vehicle size and carbon intensity of the lightweighting materials employed, the GHG emissions avoided due to improved fuel efficiency do not

offset the higher manufacturing emissions of the vehicle ( [[#Luk--2018|Luk et al. 2018]] ; [[#Wu--2019|Wu et al. 2019]] ). In addition, these advanced materials may be challenging to recycle in a way that retains their high technical performance ( [[#Meng--2017|Meng et al. 2017]] ).

'''Co-effects on particulate matter.''' Lightweighting may also alleviate the particulate matter (PM) emissions arising from road and brake wear. BEVs are generally heavier than their ICEV counterparts, which may potentially cause higher stress on road surfaces and tyres, with consequently higher PM emissions per kilometre driven ( [[#Timmers--2016|Timmers and Achten 2016]] ). Regenerative braking in HEVs, BEVs and FCVs, however, reduces the mechanical braking required, and therefore may compensate for the higher brake wear emissions from these heavier vehicle types. In addition, BEVs have no tailpipe emissions, which further offsets the increased PM emissions from road and tyre wear. Therefore, lightweighting strategies may offer a carbon and particulates mitigation effect; however, in some cases, other technological options may reduce CO 2 emissions even further.

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'''Box 10.3, Figure 1''' '''| Illustrationof energy consumption as a function of vehicle size (using mass as a proxy) and powertrain technology.''' FCVs omitted due to lacking data.

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