资源环境科技发展态势分析平台

By emitting no tailpipe emissions, electric vehicles (EVs) have the potential to completely decarbonize the US transportation sector. But the US transportation sector currently remains far from zero emissions, as the composition of the current on road vehicle fleet is mostly gasoline vehicles. EVs represent a growing yet small share of all vehicles on the road today.

This report details the current role that EVs play in reducing greenhouse gas emissions (GHG) in the US transportation sector. It also looks forward to 2025 and beyond to assess the potential for EVs to reduce future GHG emissions. We summarize our most important findings here.

First, EVs represent about one percent of all passenger vehicles on the road today, and though some truck EVs are in development, they have not yet entered the market in significant numbers. Thus, to date, EVs have had little impact on overall GHG emissions in the US. However, EV sales have grown rapidly in recent years, and there is the potential for continued exponential growth in the future.

Second, even with accelerating growth in the next few years as more EV models enter the market, they will continue to have only a modest effect on transportation sector GHG emissions. This is because the passenger vehicle fleet takes several decades to turnover, and truck fleets take even longer. Therefore, most gasoline vehicles on the road today will still be on the road in 2025, which limits the increase in the share of the fleet that will be electric by that time. Even optimistic forecasts of new EV sales will have only a limited impact on overall GHG emissions. Even if 15% of new vehicle sales are EVs in 2025, 85% of sales will still be gasoline vehicles and those will remain on the road for many years.

Third, in the longer term, as many EVs reach cost parity with gasoline vehicles some time after 2025, we expect sales volumes to increase significantly especially for passenger vehicles. However, for most larger vehicles, such as large passenger trucks and heavy-duty trucks, continuing technological progress will be essential for lowering costs to achieve competitiveness with vehicles powered by gasoline and diesel. By then trucks will contribute a larger share of GHG emissions than passenger vehicles, making them a major focus of efforts to decarbonize the transportation sector.

We present a range of forecasts about how quickly light-duty (car and light truck) EVs will enter the market in the longer term. To attain even the mid probability forecasts, government policies to promote EV demand and supply will be essential at least until full parity between EVs and gasoline vehicles is reached. Even then fleet GHG emissions do not go zero because of heterogeneity among vehicle sizes and EV buyers, and the slow turnover of the fleet.

We find that a barrier to high levels of EV penetration of the fleet in the medium to longer term is uncertainty over the cost of high-speed widely available charging capability. Fast charging availability outside the home appears critical for widespread adoption of EVs. Yet, there remain uncertainties about how to bring costs down enough for widespread commercial fast-charging in the long-run.

Finally, we review government policies that will play a critical role in accelerating the transition of the fleet, with the associated gradual reduction in GHG emissions. We discuss existing policies including state sales mandates, which target increasing the supply of EVs, and subsidies and rebates, which increase demand. We highlight the role of continual improvements in fuel economy for gasoline and diesel vehicles throughout the transition to EVs. And, we identify additional policies and ways to improve current policies to spur demand, hasten fleet turnover, and ensure sufficient charging capability.

In the discussions below, we refer to all electrified vehicles as EVs, and these include full plug-in battery electric vehicles and fuel cell vehicles powered by hydrogen. Both of these vehicle technologies have zero tailpipe emissions, but full lifecycle emissions that include producing the fuel and the vehicle are not zero. Our focus in this paper is on EV fleet penetration and tailpipe GHG, so we touch only briefly on fuel and battery emissions.