Light-Duty Vehicles Module

This Stochastic Energy Deployment System (SEDS) module covers the light-duty vehicles (LDVs) sector for the United States. It evaluates car and light truck technologies currently in the market and others at the R&D stage, which are likely to enter the light-duty market during SEDS' simulation horizon.

Available technologies compete for market share through a vehicle choice model. Various vehicle attributes are used in determining technology market shares. Macroeconomic and fuel price information from other modules are used in estimating new vehicle sales and vehicle operating costs. Vehicle survival and age-dependent usage models track LDVs that enter the market until they are scrapped.

The inclusion of specific technologies allows for extensive analysis regarding policies. For example, the module can give probability bands around hybrid deployment (and corresponding decrease in sales of competing technologies) when the ethanol subsidy amounts are varied.

Focus of Analysis

This module can analyze the effects of fuel prices; technology specific price incentives; exogenously evaluated changes in technology cost, fuel economy, and performance due to government-sponsored research programs; and consumer perspective of various technologies.

Alternatively, the module can evaluate the fuel cost and vehicle price necessary for a technology to enter and sustain in the light-duty market. The module generates fuel consumption and carbon dioxide emissions estimates for each scenario simulated.

Limitations of Analyses

A limitation of the module is that it does not model consumer driving patterns, consumer preferences or show the effects of temporary price incentives.

Also, the module cannot simulate regional differences and variations in LDV survival rates in the different parts of the United States. Other items that cannot be simulated explicitly include behavioral differences relating to new technology preferences, variations in driving patterns of consumers, multiple daily charging scenarios for plug-in hybrid electric vehicles (PHEVs) powered by internal combustion engines or fuel cells, and effects of temporary price incentives.

Technologies of Interest to U.S. Department of Energy

The module has fifteen slots for light vehicle technologies, with two vehicle types (car and light truck) for each technology. Aside from conventional spark-ignited gasoline-powered internal combustion engine (SI-ICE) vehicles and conventional compression-ignited diesel-powered internal combustion engines (CI-ICE) vehicles, it has slots for gasoline/ethanol flexible-fuel SI-ICE vehicles, advanced gasoline/ethanol SI-ICE vehicles, advanced diesel CI-ICE vehicles, gaseous fuel (compressed natural gas [CNG] and liquefied petroleum gas [LPG]) ICE vehicles, electric vehicles, three types (gasoline-, gasoline/ethanol flexible-fuel-, and diesel-powered) of charge-sustaining hybrid electric vehicles, gasoline/ethanol flexible-fuel plug-in hybrid electric vehicles with 10- and 40-mile all-electric range, hydrogen fuel cell vehicles, and PHEVs and hydrogen fuel cell vehicles with 10- and 40-mile all-electric range.

For each of these technologies, the R&D module within the LDV model contains estimates of vehicle purchase price and fuel economy based on R&D funding levels. For each technology three funding levels can be chosen by the user: base, target, and over target.

Overview of Methodology

Total new vehicle sales are estimated as a function of driving age population, prior year fuel cost, and growth in gross domestic product. The vehicle sales are then allocated to cars and light trucks. Historical vehicle sales for the period 1975-2005 are included in the module's database.

A vehicle choice model determines market share of new vehicles for earlier described technologies. All technologies need not be included in each simulation run. Each technology has its car and light truck version, and each is characterized with nine attributes:

  1. Purchase price
  2. Fuel cost per mile
  3. Range on full tank and/or charge
  4. Maintenance cost
  5. Zero-to-60 mph acceleration time
  6. Luggage space ratio to conventional vehicle
  7. Fuel availability relative to gasoline
  8. Home refueling option
  9. Make and model availability.

Aside from these nine vehicle characteristics, a term representing perceived bias for or against a technology is also included.

A nested multinomial logit formulation is used within the vehicle choice model. Market shares are determined in two steps. During the first step vehicle technologies are subdivided in three groups:

  1. ICE-powered vehicles that use gasoline, diesel, ethanol/gasoline, or CNG/LPG
  2. Electric drive vehicles excluding fuel cell technologies
  3. Fuel cell vehicles.

The vehicle choice model determines market shares for technologies within each group. The results of the first step are used in estimating market shares weighted vehicle characteristics for each vehicle technology group. The multinomial logit model is applied again to allocate market shares among the three technology groups. Each technology group's market share is subdivided among technologies within the group by using the results of the first step.

After the vehicle choice model is applied, two constraints are imposed on vehicle sales: vehicle manufacturing growth constraint and a hydrogen fuel availability constraint. The vehicle manufacturing constraint ensures that new vehicle sales for a specific technology do not grow more than a set amount in a single year. The default limiting growth rate is 30% for most technologies and 60% for conventional gasoline and diesel vehicles. These values can be adjusted by the user. The hydrogen fuel availability constraint ensures there are not more hydrogen vehicles sold than the available hydrogen fuel capacity can support.

Vehicle survival and age dependent usage functions are applied to new cars and light trucks and are used to track on road vehicles (vehicle stock) by vintage. The module uses exponential vehicle survival functions and cubic age dependent vehicle miles traveled (VMT) estimates by U.S. Department of Transportation's National Highway Traffic Safety Administration.

In addition, VMT elasticity with respect to fuel cost is applied. A default value of 0.1 is used, signifying a 10% increase in fuel cost per mile will reduce VMT by 1%. The elasticity can be modified by the user. These functions are applied to estimate VMT for each vintage. Vehicle fuel economy for each vintage is carried forward, and fuel consumption by each vehicle vintage is estimated. The sum of fuel consumption by all vintages provides annual fuel consumption for each technology.

Flexible-fuel vehicles can use either E85 (85% denatured ethanol and 15% gasoline by volume) or gasoline. The amount of E85 used is specified within the liquid fuels module. In terms of heating value, neat ethanol's share of E85 is taken as 74.27%. This is based on the latest data that 4.7% gasoline is added as a denaturant to ethanol prior to shipping.

A PHEV, with either an ICE or a fuel cell as its power plant, can travel some distance on grid electricity stored in its battery pack. Each PHEV is identified with an all-electric range (AER) at the time of its sale. These AER values are used in estimating fraction of annual VMT on electricity for each vintage and electricity use by PHEVs is estimated. Data from the 2001 National Household Travel Survey were used for developing a function that estimates fraction of miles on electricity, given PHEV all electric range.

All of the carbon content of a fuel is converted to either carbon dioxide (CO2) or to other (non-CO2) emissions. The CO2 emissions are estimated as the carbon contents of a fuel minus the non-CO2 carbon emissions, times the CO2 conversion factor. The amount of carbon emitted as non-CO2 emissions is estimated through multiple runs of U.S. Environmental Protection Agency's MOBILE6.2 model. Emissions of non-methane hydrocarbons, carbon monoxide, and methane are estimated for Tier 0, Tier 1, and Tier 2 vehicles, and the amount of carbon in these pollutants is estimated.

Major Assumptions

The base case vehicle characteristics are compiled from multiple sources. Vehicle prices and all vehicle attributes excepting fuel cost are obtained for midsize cars and small sports utility vehicles from a project at the U.S. Department of Energy Office of Vehicle Technologies. Fuel prices and vehicle test fuel economy values are taken from Energy Information Administration's Annual Energy Outlook (AEO) 2008. The AEO 2008 fuel economy values were modified for PHEVs (ICE and fuel cell). All new PHEVs were assigned some all electric range. A factor of 0.85 is applied to all test fuel economy values to account for on-road degradation.

Historically, annual miles per LDV have increased over time. An exponential function was estimated to represent this increase and is applied to annual miles by each vehicle vintage. The average growth in annual miles per vehicle is estimated as 0.48% per year for the period 2005-2050.

Stochastic Inputs

When the SEDS model is run in "stochastic" mode, the LDV module has two stochastic variables: vehicle purchase price and fuel economy. These both reside within the LDV R&D module. Their distributions input parameters are the 10th, 50th, and 90th percentile values. During each stochastic run, vehicle price and fuel economy are chosen from their respective distributions.

Key Inputs from Other Modules

  1. Price of gasoline, diesel, E85, CNG, electricity, and hydrogen
  2. Change in gross domestic product
  3. Population in age group 16-84 (driving age population)
  4. Hydrogen fuel capacity

Key Outputs to Other Modules

  1. Light-duty demand for gasoline, diesel, E85, CNG, electricity, and hydrogen
  2. CO2 emissions


SEDS Transportation Sector Modules


Anant Vyas, Argonne National Laboratory

Deena Patel, Argonne National Laboratory