Researchers: Christopher Yang, David McCollum, Ryan McCarthy, Wayne Leighty

Abstract

In his Executive Order S-3-05, California Governor Arnold Schwarzenegger highlighted the potential impacts of climate change on California and established greenhouse gas reduction targets for the state.  These targets include reducing emissions to 2000 levels by 2010, achieving 1990 levels by 2020 and reaching an 80% reduction below 1990 levels by 2050.  These targets are among the most ambitious by a major world economy.  Given the expected growth in population and energy service demand in California, meeting these targets, especially the 80% reduction by 2050, will be quite challenging. 

The goal of this study is to identify technology and other potential options for meeting this ambitious, long-term goal in the transportation sector, including light-duty, heavy-duty, agricultural, off-road, rail, aircraft, and marine vehicles.  The analysis focuses on three main areas: travel demand, fuel efficiency and fuel carbon intensity.  The study highlights the various options that could be used to meet the emission reduction targets and creates "snapshots" of option combinations that allow the state to meet the targets across the various transportation modes.  The extent to which advanced vehicles and alternative fuels can contribute to greenhouse gas reduction goals are elucidated, and additional steps that may have to be taken in the transportation sector are characterized.  The study is based upon spreadsheet models of the transport sector, which are used to help identify the challenges, potential benefits, and trade-offs for alternative fuel vehicles and other options associated with meeting the transport-related greenhouse goals for California.

An 80in50 reduction in GHG emissions from the California transportation sector is challenging but potentially feasible. While no one mitigation option can singlehandedly meet the target, the goal can be met in multiple ways, utilizing a combination of technological and behavioral options.

The analytical framework used in this study, and many of its overall conclusions, are not limited to California, however.  Researchers and policymakers from other states and nations will likely face the same issues and challenges as California in their efforts to make deep reductions in transport greenhouse gas emissions over the long-term.

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Project Deliverables

Policymaker Summary  (13 pp, 0.7 MB)
    - Brief report summarizing the motivation, methods, results, conclusions, and policy recommendations of this study

Full Report (Draft) (124 pp, 3.7 MB)
    - Longer report describing all aspects of the project, including results, conclusions and detailed modeling methodology and assumptions
     Download individual sections of the report:

     Policymaker Summary  (13 pp, 0.7 MB)  |  Main Body of Report (75 pp, 2.1 MB)  |  Appendix (39 pp, 1.4 MB) (pending)

Journal paper
    - Submitted to Transportation Research Part D: Transport and Environment.  Forthcoming. . .

Summary Presentation
    - Presentation slides providing an overview of the project, including key results and conclusions

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Project Overview, Results, and Conclusions

Background & Context

Instate emissions refer to GHGs generated from travel taking place completely within the borders of California.
(i.e., both origin and destination of trips are located in California)




Overall emissions refer to GHGs generated from travel with either an origin or destination within California.
(i.e., trips that cross the state's boundaries)




Overall emissions are greater than Instate emissions since the former captures a greater share of out-of-state aviation and marine travel.

Methodology - LEVERS Model and Kaya Framework

The 80in50 project uses a transportation-variant of the Kaya identity to analyze changes in GHG emissions from 1990 levels. This analytical framework is embedded into a spreadsheet model called the Long-term Evaluation of Vehicle Emission Reduction Strategies (LEVERS) model, which organizes the Kaya parameters for technologies and fuels into scenarios; transport emissions are then calculated.  The main drivers for transportation GHG emissions are population, travel demand, vehicle fuel consumption, and fuel carbon intensity. 














Total transportation activity is represented as the product of population (P) and transport intensity (T), which is defined as passenger- or freight-miles per capita (e.g., miles/person). The product of the latter two parameters, energy intensity (E) and carbon intensity (C), defines the amount of carbon emitted per-mile of transport. Altogether, the four parameters describe total GHG emissions from a transportation sector.

Results & Discussion

Silver Bullet Scenarios


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Silver Bullet (SB) scenarios describe futures in which one mitigation option, such as an advanced vehicle technology or alternative fuel, is employed to the maximum extent possible from a technology perspective in 2050.


The figure shows each of the Silver Bullet scenarios and the reduction in GHG emissions relative to the 1990 level and the 2050 Reference scenario. None of the Silver Bullet scenarios achieve the 80in50 reduction goal, implying that no single technology can successfully meet California’s 80% emission reductions goal; a portfolio approach is necessary.


* In the Biofuel Intensive SB scenario, ~60% of transportation fuel supply comes from biofuels. This level is consistent with California consuming 15-20% of total U.S. supply.
* Significant uncertainties surrounding indirect land use change impacts from biofuels production lead to the large variability in potential GHG changes from 1990 levels.







80in50 Scenarios


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None of the individual mitigation strategies examined in the Silver Bullet scenarios can achieve the ambitious 80in50 goal by themselves.  However, several of the options examined in these scenarios are complementary (such as improving efficiency, utilizing alternative fuels and reducing travel demand) and can be combined in a portfolio approach to achieve California’s GHG emission reductions target.

Three scenarios are presented that represent different potential futures for California in which the 80in50 reduction goal in Instate GHG emissions is realized. The scenarios are snapshots of the transportation sector in 2050 and illustrate different mixes of mitigation options in various sectors that can achieve the necessary reductions.  Population is the same in each scenario, equal to twice its value in 1990.






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In the Efficient Biofuels 80in50 scenario, switching from petroleum to biofuels accounts for 232 MMTCO2e of GHG emission reductions, and switching to electricity reduces emissions an additional 40 MMTCO2e. As seen in the figure, most of the reductions from biofuels (144 MMTCO2e) can be attributed to their lower carbon intensity (relative to conventional fuels in the Reference scenario). For electricity, vehicle efficiency improvements (mostly through plug-in hybrid electric vehicle penetration in the light-duty sector) account for nearly two-thirds of the emission reductions (27 MMTCO2e), while the lower carbon-content of electricity as a fuel (14 MMTCO2e) comprises the balance. The broad applicability of biofuels in conventional combustion engines allows dramatic reductions in the GHG-intensity of all modes of transport in this scenario. 

This scenario demands a large quantity of low-carbon biofuels, however. (In the Instate case, 16.2 billion gge are needed, while the Overall emissions case requires 21.1 billion gge.) As in the Biofuel-intensive SB scenario, this would consume about 15-20% of total potential U.S. biofuel production under optimistic estimates. Biofuels consumption is roughly the same level as in the Biofuel-intensive SB scenario, but because of the lower efficiency of vehicles in the Silver Bullet scenario, 16 billion gge can only supply 60% of fuel used in that scenario.  Given a constrained supply of biofuels, efficiency is an important strategy for helping to stretch the biomass resource base.



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In the Electric-drive 80in50 scenario, the largest portion of emission reduction comes from the use of FCVs and hydrogen fuel (159 MMTCO2e), although electric vehicles also contribute to emission reductions (105 MMTCO2e) mainly from PHEVs and BEVs in the LDV sector. Approximately two-thirds of the emission reductions in the scenario can be attributed to improvements in fuel economy associated with electric-drive vehicles (FCVs, EVs, and PHEVs), while most of the remainder can be attributed to the use of low-carbon intensive hydrogen and electricity. Biofuels are responsible for emission reductions in other sectors where hydrogen and electric vehicles are ill-suited. Consumption of low-carbon biofuels is only about 1.0 billion gge in 2050. (The Overall emissions case requires 4.4 billion gge of biofuels.)












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The two largest contributors in the Actor-based 80in50 scenario are reductions in overall travel demand (unlike the other two 80in50 scenarios) and the use of electricity in vehicles (mainly via gasoline and diesel PHEVs). Smaller, efficient electric-drive vehicles, primarily in the LDV and HDV sectors, and the fact that consumers accept reduced vehicle performance in response to very high energy prices both lead to a large improvement in vehicle efficiency. Biofuels consumption in this scenario is just 1.3 billion gge in 2050. (The Overall emissions case requires 4.2 billion gge of biofuels.)















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The Actor-based 80in50 scenario provides the most diverse solution, drawing on a number of strategies to reduce emissions, including both travel demand reductions and technology improvements across a suite of vehicle types and fuels.

The other two 80in50 scenarios, which are more technology-driven, present futures with similar underpinnings, but emphases on different fuels and technologies lead to distinct scenarios for vehicle energy intensities and fuel carbon intensities. Electric-drive 80in50 yields a more energy-efficient system on whole, as a higher fraction of FCVs and BEVs in the fleet mix reduces aggregate energy intensity, while Efficient Biofuels 80in50 relies more on reduced carbon-intensity of fuels to meet the 80in50 goals. Travel demand reductions do not contribute to emission reductions in either of the technology-driven scenarios. If demand were to be reduced, then the required reductions in energy consumption and fuel carbon-intensity to meet the 80% target would decrease accordingly. 

Because the three 80in50 scenarios, especially Electric-drive 80in50 and Efficient Biofuels 80in50, rely heavily on very low-carbon intensive fuels to achieve the GHG target, they are quite sensitive to assumptions about fuels production. The use of higher carbon-intensive fuels (e.g., hydrogen and electricity produced from 'dirtier' methods or biofuels associated with significant land use change impacts) would eliminate many of the emission reductions gained in these scenarios. This is less the case for Actor-based 80in50, however, since reductions in travel demand and increases in vehicle efficiencies bear more of the responsibility for lowering emissions.






Increased vehicle efficiency in Electric-drive 80in50 reduces fuel use more than for Efficient Biofuels 80in50. Less-efficient biomass-to-biofuels conversion processes and lower ICE drivetrain efficiencies lead to increased primary resource requirements in Efficient Biofuels 80in50 compared to the more-efficient hydrogen and electricity production processes and higher FCV and BEV drivetrain efficiencies utilized in Electric-drive 80in50. Efficient Biofuels 80in50 requires 12% more primary energy (mainly biomass) than even in the Reference scenario. The use of hydrogen and electricity in the Electric-drive 80in50 scenario leads to a greater diversity of primary energy resources that includes relatively equal shares of biomass and natural gas, as well as a significant fraction of coal, among other resources.

In the Actor-based 80in50 scenario, fuel use and primary resource use are reduced dramatically below the Reference scenario, as well as the other two 80in50 scenarios. By reducing travel demand and significantly increasing vehicle efficiency across all sectors, a substantial amount of both fuel and primary energy resources are saved. The Actor-based 80in50 scenario reduces fuel requirements by almost 21 billion gge, or about 73%, compared to the Reference scenario, and by 40% and 57%, respectively, compared to Electric-drive 80in50 and Efficient Biofuels 80in50. Similar percent reductions hold for primary resource consumption as well.

Policy Recommendations & Conclusions

1. The modified Kaya equation is a useful decomposition that highlights the major drivers of transport GHG emissions and the targets for mitigation options: population, transport intensity, energy intensity and carbon intensity. 

2. Very low carbon intensity alternative fuels (biofuels, hydrogen and electricity) appear to be feasible means of lowering transportation carbon intensity (C), but carbon intensity can vary widely for these fuels based upon the details of their life-cycle.

3. There is significant potential for greatly improved vehicle efficiency (reduced E) for use in all of the transport subsectors. 

4. The business-as-usual Reference scenario exhibits large growth in GHG emissions (63%) due to growth in population (P) and transport intensity (T).

5. The Silver Bullet (SB) scenarios show that while many mitigation options can yield moderate GHG reductions, no single mitigation option or strategy can meet the 80% reduction goal individually. 

6. Three distinct 80in50 scenarios are presented that meet the 80% reduction goal in different ways, and they show that meeting the goal is a challenging prospect and requires very extensive penetration of advanced technologies and low carbon fuels.

7. Not all vehicle technology and fuel options can be applied to each of the transportation subsectors because of specific requirements for characteristics such as power, weight, or vehicle range.

8. Biofuels are probably most applicable across all transport subsectors.  However they can only be made from biomass and are likely to be limited by biomass resource availability and may also be limited by land use change (LUC) impacts, which may reduce or negate their GHG benefits.

9. Hydrogen and electricity can be made from a wide range of domestic resources, and resource constraints are unlikely to be major impediments to their adoption; however, they may be limited by their applicability to all of the transport subsectors (especially aviation, marine and off-road). 

10. Slowing the growth in travel demand (i.e., reducing transport intensity, T) can help reduce the extent to which technological advances will be required to reduce the amount of carbon emitted per mile of travel (ExC). 

11. It is more challenging to meet the 80% reduction goal with Overall emissions because aviation and marine are two of the more challenging sectors to address from a technology perspective, and demand for these travel modes is growing rapidly, especially in the aviation sector. 

12. Current policies only address some of the transportation subsectors and do not currently address options for reducing travel demand.  These gaps may impede the development of options to address transport GHGs.