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Autonomous vehicles (AVs) are conveyances to move passengers or freight without human intervention. AVs are potentially disruptive both technologically and socially 1-3 , with claimed benefits including increased safety, road utilization, driver productivity and energy savings 1-6 . Here we estimate 2014 and 2030 greenhouse-gas (GHG) emissions and costs of autonomous taxis (ATs), a class of fully autonomous 7,8 shared AVs likely to gain rapid early market share, through three synergistic e ects: (1) future decreases in electricity GHG emissions intensity, (2) smaller vehicle sizes resulting from trip-specific AT deployment, and (3) higher annual vehicle-miles travelled (VMT), increasing high-e ciency (especially battery-electric) vehicle cost-e ectiveness. Combined, these factors could result in decreased US per-mile GHG emissions in 2030 per AT deployed of 87-94% below current conventionally driven vehicles (CDVs), and 63-82% below projected 2030 hybrid vehicles 9 , without including other energy-saving benefits of AVs. With these substantial GHG savings, ATs could enable GHG reductions even if total VMT, average speed and vehicle size increased substantially. Oil consumption would also be reduced by nearly 100%.Many automakers and Google plan to rapidly commercialize AVs (refs 4,8,10), although it will take time to gain widespread market share. AV functionality ranges from lane-keeping and parking assistance features to full control without human input 7 . As of 2014, four US states and Washington DC allow AV testing on roadways, with thirteen more contemplating similar laws; Nevada is the first state offering 'certificates of compliance' for non-testing use of AVs (ref. 4). For more background information, see Supplementary Note and Supplementary Table 1. The US Energy Information Administration (EIA; ref. 11) projects GHG intensity decreases between 2014 and 2030 in gasoline (3.8%) and electricity (8.5%), due to growing renewable energy contributions. However, GHG policies may lower intensities further. The US Environmental Protection Agency (EPA) has proposed a rule to lower average GHG intensity of electricity 30% by 2030 (ref. 12), whereas in California (CA) GHG electricity intensities may fall 55% by 2030 as a result of several policies 13 . We considered GHG intensities of gasoline and electricity based on 2014 and 2030 EIA projections, and 2030 GHG electricity intensities from EPA and CA (applied across the US). Also considered were GHG emissions for hydrogen produced from natural gas reforming, water electrolysis or other methods 14 ; the former two were estimated using GHG energy intensities from EIA for natural gas, and EPA and CA for electricity.Combining GHG energy intensities with vehicle technology efficiencies produced a wide variety of GHG emissions intensities per mile. Passenger car and light truck fuel efficiencies were combined using fleet mix ratios projected for 2014 and 2030 (ref. 11). As shown in Fig. 1 (see Supplementary Table 2 for additional data), there is a 52% decrease in GHG emis...

9Electric vehicles enable clean and efficient transportation, however concerns about range anxiety 10 and battery degradation hinder EV adoption. The common definition for battery end-of-life is 11 when 70-80% of original energy capacity remains, however little analysis is available to support 12 this retirement threshold. By applying detailed physics-based models of EVs with data on how 13 drivers use their cars, we show that EV batteries continue to meet daily travel needs of drivers 14 well beyond capacity fade of 80% remaining energy storage capacity. Further, we show that EV 15 batteries with substantial energy capacity fade continue to provide sufficient buffer charge for 16 unexpected trips with long distances. We show that enabling charging in more locations, even if 17 only with 120V wall outlets, prolongs useful life of EV batteries. Battery power fade is also 18 examined and we show EVs meet performance requirements even down to 30% remaining 19 power capacity. Our findings show that defining battery retirement at 70-80% remaining 20 capacity is inaccurate. Battery retirement should instead be governed by when batteries no longer 21 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT satisfy daily travel needs of a driver. Using this alternative retirement metric, we present results 22 on the fraction of EV batteries that will be retired with different levels of energy capacity fade. 23 24 Key Words: electric vehicles, battery degradation, capacity fade, power fade, battery second 25 life, battery retirement 26

The risk of accelerated electric vehicle battery degradation is commonly cited as a concern inhibiting the implementation of vehicle-to-grid (V2G) technology. However, little quantitative evidence exists in prior literature to refute or substantiate these concerns for different grid services that vehicles may offer. In this paper, a methodology is proposed to quantify electric vehicle (EV) battery degradation from driving only vs. driving and several vehicle-grid services, based on a semi-empirical lithium-ion battery capacity fade model. A detailed EV battery pack thermal model and EV powertrain model are utilized to capture the time-varying battery temperature and working parameters including current, internal resistance and state-of-charge (SOC), while an EV is driving and offering various grid services. We use the proposed method to simulate the battery degradation impacts from multiple vehicle-grid services including peak load shaving, frequency regulation and net load shaping. The degradation impact of these grid services is compared against baseline cases for driving and uncontrolled charging only, for several different cases of vehicle itineraries, driving distances, and climate conditions. Ten-year degradation simulation results show that frequency regulation and peak load shaving at power rates typical for vehicle charging and discharging will not significantly accelerate battery degradation in comparison to the degradation incurred from driving and calendar aging.

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California has issued ambitious targets to decarbonize transportation through the deployment of electric vehicles (EVs), and to decarbonize the electricity grid through the expansion of both renewable generation and energy storage. These parallel efforts can provide an untapped synergistic opportunity for clean transportation to be an enabler for a clean electricity grid. To quantify this potential, we forecast the hourly system-wide balancing problems arising out to 2025 as more renewables are deployed and load continues to grow. We then quantify the system-wide balancing benefits from EVs modulating the charging or discharging of their batteries to mitigate renewable intermittency, without compromising the mobility needs of drivers. Our results show that with its EV deployment target and with only one-way charging control of EVs, California can achieve much of the same benefit of its Storage Mandate for mitigating renewable intermittency, but at a small fraction of the cost. Moreover, EVs provide many times these benefits if two-way charging control becomes widely available. Thus, EVs support the state's renewable integration targets while avoiding much of the tremendous capital investment of stationary storage that can instead be applied towards further deployment of clean vehicles.

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