NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

A Reliable Muddle: Transportation Scenarios for 

the 80% Greenhouse Gas Reduction Goal for 2050

California Air Resource 

Board Scenario Meeting

Marc Melaina

Karen Webster 

October 28, 2009

Sacramento, California

NREL/PR-560-47003
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Presentation Overview

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Intro: Reducing LDV GHGs to 80% below 1990 levels

• Transportation sector-specific emissions data and policy concerns.

Part 1: Metrics for the 80% goal: A Pyramid Framework

• Three Metrics of the Pyramid Framework

 Vehicle Miles Traveled (VMT)

 Vehicle Fuel Economy (FE)

 Fuel Carbon Intensity (CI)

• Detailed Scenarios

• VISION tool

Part 2: Major LDV GHG Abatement Strategy: A Portfolio Approach

• Policy interactions and the technology innovation process

Conclusion: A multi-faceted policy and technology approach will be 

required to reach the 80% goal.
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Portfolio of Major Transportation Policies that Influence 

VMT, FE and CI for GHG Reductions

VMT Reduction

• Reduce vehicle miles traveled (VMT) with public transportation, 

land-use planning, mode switching

• Also: higher fuel prices

Corporate Average Fuel Economy (CAFE)

• Sets an average fuel economy (FE) for new light duty vehicles.

Renewable Fuel Standard (RFS)

• Reduces fuel carbon intensity (CI) through use of biofuels.

Low Carbon Fuel Standard (LCFS)

• Reduces fuel carbon intensity (CI) through use of variety of 

alternative fuels and vehicles.

Zero Emission Vehicle Mandates (ZEV)

• Increases fuel economy (FE).
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Factor Increases between 2008 & 2050 

VMT: +80%, FE: +20%, CI: -1%  GHGs: +50%

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Reduction Target

AEO 2008

Three Metrics Provide a Simple Conceptual Framework: 

Guiding Equation is C = VMT * CI / FE

GHGs in 2050: 692 MMTCe

GHGs in 2008: 455 MMTCe

National Annual Energy Outlook ‘Reference’ Metrics for 

Light-Duty Vehicles
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What GHG reductions are achievable from 

reducing each of the 3 metrics? 

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2 Illustrative Scenarios for 

the U.S.: 

‘GHG-1’ and ’GHG-2’

•Each GHG scenario achieves 

the 2050 goal

•Scenarios are illustrative, not 

predictive

•Intent of scenarios is to 

demonstrate types of change 

needed for 80% GHG goal

•Baseline is AEO 2008.

GHG-1: Modest improvements in VMT and FE; 

CI improvements achieve remainder of 2050 goal reductions

GHG-2: Aggressive improvements in VMT and FE; 

CI improvements achieve remainder of 2050 goal reductions

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Multiple Pathways: A variety of suggestions have 

emerged with differing emphasis on metrics

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Source: DRAFT NREL Analysis
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Specific scenario characteristics can be 

elucidated with Argonne’s VISION model.

Argonne model for estimating fleet-wide energy use, oil

use and carbon emissions. Inputs include:

Advanced vehicle market penetration, VMT/LDV, Fuel 

characteristics, New car fuel efficiency, Fuel-Cycle carbon 

coefficients (from GREET, based on AEO)

VISION’s calculations are based on vehicle survival and 

age-dependent vehicle usage characteristics. 

Market penetration and fuel economy assumptions are 

determined exogenously (scenario development). 

Uses market penetration 

and fuel characteristics to 

project future vehicle fleet 

and fuel pool.

Calculates total 

vehicle miles traveled 

and fuel consumed.

Factors in vehicle fuel 

efficiency and fuel 

carbon coefficients.

Produces fleet-wide 

energy usage and 

emissions
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A large number of input options are combined 

Gasoline, 

CI = 93.4 gCO2e/MJ

Diesel , 

CI = 93.2 gCO2e/MJ

Ethanol , 

CI = -10 – 75 gCO2e/MJ

Hydrogen, 

CI = 15 – 300 gCO2e/MJ

Electricity, 

CI = 50 – 225 gCO2e/MJ

Biodiesel , 

CI = 0 – 90 gCO2e/MJ

Gas ICE,

Efficiency 

ratio = 1.0

Diesel ICE,

Efficiency 

ratio = 1.2

E-85 FFV,

Efficiency 

ratio = 1.0

FCV, 

Efficiency 

ratio = 2.3

PHEV, 

Efficiency 

ratio = 3.0

Fleet-wide 

VMT, FE & CI
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VISION models the entire population of light-duty 

and heavy-duty vehicles and fuels over time.

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Total Light Vehicle Market Penetration

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2000 2010 2020 2030 2040 2050

FCV

D PHEV

SI PHEV

D HEV

SI HEV (E85/H2)

SI HEV (Gsln)

CNG

Diesel

E-85 FFV

EV

Gasoline ICE

Total Light Vehicle Stock

0%

20%

40%

60%

80%

100%

2000 2010 2020 2030 2040 2050

FCV

D PHEV

SI PHEV

D HEV

SI HEV (E85/H2)

SI HEV (Gsln)

CNG

Diesel

E85 FFV

EV

Gasoline ICE

Share of Total Energy

0%

20%

40%

60%

80%

100%

2000 2010 2020 2030 2040 2050

Ethanol (E85)

Ethanol (blend)

Electric 

Hydrogen

Bio-Diesel

F-T Diesel

CNG

Diesel

Gasoline

NOT REAL DATA – EXAMPLE ONLY
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VISION is a ‘stock flow’ or ‘bucket’ model that explicitly 

tracks vehicle and fuel characteristics over time.

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Vehicle Survival in VISION

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Number of years model has been on the road

Survival Rate

VISION

Source: DRAFT NREL Analysis

Source: NHTSA, http://www-nrd.nhtsa.dot.gov/Pubs/809952.pdf
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VISION-CI

Modified version of the Argonne VISION model.

Incorporates fleet-wide average fuel carbon intensity 

calculations for different fuels and aggregate vehicle 

fleet scenarios.

Scalable for region-specific analyses.

Capable of storing and analyzing multiple regions and 

technology scenarios.

Currently incorporating data for California, Texas and on 

a national level.

A work in progress.
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Examples of Single Technology Scenarios that would 

fall within the GHG-2 National Compliance Pathway

Many different combinations of vehicles and fuels are conceivable.

These are simplified examples of (unlikely) “silver bullet” success 

stories.

Source: DRAFT NREL 80 in 2050 Transportation Scenario Analysis

VMT (billion miles) 4,621

FE (mpg) 35.1

CI (MMTCe/Quad) 4.3

Producing enough ethanol for this scenario 

may not be feasible. Current projection for 

corn stover cellulosic CI is 3.0 MMTCe/Quad

FFV fleet running on Cellulosic 

Cellulosic

VMT (billion miles) 2,911

FE (mpg) 29.7

CI (MMTCe/Quad) 4.3

Low-C Electricity

VMT (billion miles) 1,710

FE (mpg) 75.2

CI (MMTCe/Quad) 11.7

Current projection for a renewable grid CI in 

2050 is 22.4 MMtCe/Quad. Assume 37% VMT 

on electricity.

PHEV fleet running on Cellulosic 

Ethanol and Low-Carbon Electricity

VMT (billion miles) 4,621

FE (mpg) 42.5

CI (MMTCe/Quad) 5.2

Current Projection for biomass derived 

hydrogen CI is 10.22 MMTCe/Quad, and for 

solar derived 5.67 MMTCe/Quad

FCV fleet running on Hydrogen
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Biofuels Limitations 

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The amount of biofuel available for transportation is still unclear. 

Source: DRAFT NREL Analysis
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Considerations

The Transportation Sector is Unique

• Long-term support for a portfolio of transportation-specific 

policies is key to deep reductions in GHGs

Scenarios developed in VISION elucidate issues to be 

addressed for achieving 80% in 2050.

No Silver Bullet

• Though support for specific technologies is warranted (e.g., 

batteries), there is no clear winner among viable long-term, lowcarbon vehicle/fuel combinations

• Communication among stakeholders (e.g., autos and fuel suppliers) 

is key to effective alignment of more stringent policies

Local and Regional Variability

• Due to the broad range of vehicles, fuels, market conditions, and 

the geographic distribution of low-carbon energy resources, policy 

impacts will vary from city-to-city and region-to-region
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Questions?