Photo by Dennis Schroeder / NREL

Light-duty vehicles (LDV) are a huge source of greenhouse gas (GHG) emissions in the United States. To avoid the worst effects of global climate change, we need to cut these emissions by 80% by 2050. What will this mean for LDVs? Just lowering gasoline consumption in conventional LDVs with internal combustion engines (ICEs) will not make enough of a dent in GHG emissions.

LDVs account for 61% of U.S. GHG emissions. The number of LDVs and the distance they travel, or vehicle-kilometers traveled (VKT), are projected to reach 6.3 trillion kilometers by 2050. Compounded by the long time vehicle technology takes to bring to market, these realities and the factors outlined below make multiple strategies for reducing LDV energy use and emissions a necessity.

After reviewing the scientific and engineering literature, the clear consensus is that individual strategies won’t move the needle far enough. Deep cuts can only be accomplished by combining advances in vehicle technology with low-GHG energy sources. These include pairings of:

Improvements in internal combustion engines (ICEs) and bio-based liquid fuels. Even after maximizing energy efficiency measures, traditional ICE LDVs—including hybrids—can only meet GHG targets by replacing a large percentage of gasoline with biofuel.

Greater deployment of battery electric vehicles (BEVs) and the generation of larger amounts of electricity from renewable sources. Although BEVs use only about a third as much energy per kilometer driven as ICE vehicles, BEV driving range is considerably shorter, making it difficult to use BEVs for all trips. Also, in regions where coal-fired power plants generate most of the electricity used to charge these vehicles’ batteries, BEVs will not meet GHG reduction targets.

Hydrogen fuel cell vehicles and development of renewable hydrogen sources. Fuel cell electric vehicles avoid BEVs’ range issues, but still would need hydrogen produced from renewable solar or wind sources in order to meet GHG targets.

Plug-in hybrids don’t have BEVs’ range issues and are less-polluting than ICE vehicles, but they can only travel a limited number of miles powered by electricity, rather than gas. Widespread deployment of autonomous vehicles could dramatically diminish VKT and GHG emissions, but it is still uncertain how quickly these vehicles will enter the market.

While each of these individual strategies only represents an incremental improvement, together they can deliver the meaningful reductions needed to meet GHG emissions goals.

Chris Gearhart’s review ‘Implications of sustainability for the United States light-duty transportation sector‘ is freely available online

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