Data Collection Methodologies

This page describes the data collection methodologies for the Alternative Fuels and Advanced Vehicles Data Center's (AFDC) database-driven Web tools. The following information outlines how the data is collected and show's the AFDC's maintenance schedules.

Alternative Fuel Station Maps

Methodology: The data in the Alternative Fueling Station Locator and Route Mapper are gathered and verified through a variety of methods. The National Renewable Energy Laboratory (NREL) obtains information about new stations from trade media, Clean Cities coordinators, a submittal form on the Alternative Fuels and Advanced Vehicles Data Center Web site, and through collaborating with infrastructure equipment and fuel providers. The information for each new station is verified by contacting the station before adding it to the database. Existing stations in the database are contacted once a year on an established schedule to verify they are still operational and selling the fuel specified. Stations that are no longer operational or no longer sell alternative fuel are removed from the database on a monthly basis or as they are identified.

NREL regularly compares its station data with those of other relevant trade organizations and Web sites. Differences in methodologies and inclusion criteria may result in slight differences between NREL's database and those maintained by other organizations. NREL also collaborates with alternative fuel industry groups to maintain the data. NREL and its data collection subcontractor are currently collaborating with NGVAmerica and the propane industry to identify new stations and establish best practices for identifying new stations in the most-timely manner possible and to develop a more rigorous network for the future.

Station addresses are geocoded and mapped using a mapping application. If an exact address is not found by the mapping application, the station is mapped in the center of the zip code, which could appear on the map at a considerable distance from the station's actual location.

Caution: The AFDC recommends that users verify that stations are open, available to the public, and have the fuel prior to making a trip to that location.

Document Database

Methodology: NREL maintains a database comprised of thousands of documents related to alternative fuels, advanced vehicles, fuel economy, idle reduction, and more. As new publications are produced by the U.S. Department of Energy (DOE) Clean Cities inititative and other transportation-related DOE programs (including FreedomCAR, Biomass, and Hydrogen), they are added to the database. Documents developed by other government sources and industry are reviewed for their relevancy and added to the database if they fit criteria.

NREL obtains author approval before adding non-DOE documents to the database. When approval is not obtained but the document is deemed valuable, a citation and link to the document on another Web source is posted.

Federal Fleets

Methodology: Data used for NREL's analysis of the Federal Fleet are derived from the Federal Automotive Statistical Tool (FAST). Certain "covered" Federal departments and agencies are required to report annually on the number of alternative fuel vehicles in their fleets as well as the total number of all vehicles, whether light-, medium-, or heavy-duty. They are also required to specify and quantify the type of fuel used.

The Federal agencies required to report this information include:

Department of Agriculture
Department of Commerce
Department of Defense (including Army, Air Force, Navy, U.S. Marine Corps, Corps of Engineers, and Defense Agencies)
Department of Energy
Department of Health and Human Services
Department of Homeland Security (since 2003)
Department of Housing and Urban Development
Department of the Interior
Department of Justice
Department of Labor
Department of State
Department of Transportation
Department of the Treasury
Department of Veterans Affairs
Environmental Protection Agency
General Services Administration
Court Services and Offender Supervision Agency
National Aeronautics and Space Administration
Smithsonian Institution
Social Security Administration
United States Postal Service

Total vehicle counts are for domestically-based vehicles and include law enforcement vehicles and emergency vehicles. Total alternative fuel and total petroleum fuel also includes fuel used by domestically-based vehicles, including law enforcement vehicles and emergency vehicles.

Flexible Fuel Vehicle Cost Calculator

Methodology: The Flexible Fuel Vehicle Cost Calculator compares vehicles that can run on E85. The fuel prices are taken from the most recent version of the Alternative Fuel Price Report, which is released quarterly. Prices fluctuate significantly over time and across regions, so the user can change those fields. The fuel economy numbers come from the EPA.

Caution: This tool is intended for informational purposes only; it should not be used exclusively to make purchasing or budget decisions.

Natural Gas Vehicle Cost Calculator

Methodology: The Natural Gas Vehicle Cost Calculator offers a quick picture of the costs associated with the only available light-duty natural gas vehicle, the Honda Civic GX. It includes incremental cost figures and fuel economy numbers from Honda. Alternative fuel vehicle incentives are based on data entered by the user and are fleet-type and state dependant. Fuel prices are based on the Alternative Fuels Price Report, which is released quarterly. Prices fluctuate significantly over time and across regions, so the user can change these fields.

Caution: This tool is intended for informational purposes only; it should not be used exclusively to make purchasing or budget decisions.

State Assessment for Biomass Resources

Methodology: This tool has both a geographic and an analytic component. The geographic component is composed of two types of static maps for each state: Potential Production and Potential Use. The tool has a complete methodology page that focuses on the calculation areas and outlines their methodology, including the underlying data and assumptions. Go to the State Assessment for Biomass Resources Methodology page to learn more.

State and Federal Incentives and Laws

Methodology: NREL's database captures state and federal laws and incentives related to alternative fuels and vehicles, air quality, vehicle efficiency, and other transportation-related topics. State-level information is updated annually after each state's legislative session ends. Information for these updates is obtained from state legislative sites when the sites are deemed accurate and timely or by calling specific state offices directly. In addition, NREL maintains a resource list of the most useful Web sites and contacts for every state, as well as a list of search terms states routinely used in Web site searches. Information on the process of bills becoming state law was provided courtesy of StateScape.

Federal information is updated after enacted legislation is signed into law or when rules are issued by the responsible agencies. Existing information is reviewed at the same time new information is added to ensure it is still accurate and in effect.

Caution: The AFDC recommends that users verify with the appropriate state or federal authority that the specific law or incentive is still applicable before making a purchase or tax-related decision.

Truck Stop Electrification Site Locator

Methodology: NREL collects the data in the Truck Stop Electrification (TSE) Site Locator from IdleAire and Shorepower. NREL, in turn, verifies the information (including station name, address, phone number, hours of operation, directions, etc.) by calling the fueling sites directly.

The verification process for all records occurs approximately every six months. In addition, NREL continually checks Web sources to determine if new sites have been added. If a new TSE site is found, NREL adds it as soon as possible.

The addresses for the sites are geocoded and mapped using a mapping application. If an exact address is not found, the TSE site is mapped in the center of the zip code, which may appear on the map at a considerable distance from the station's actual location.

Caution: The AFDC is aware that slight differences may be noted when comparing its data to that on the IdleAire and Shorepower sites. As previously mentioned, NREL verifies all TSE site data by calling the TSE sites directly. However, the AFDC recommends users additionally verify TSE site locations to ensure they are operational prior to making a trip.

Vehicle Search - Light Duty

Methodology: Vehicle specifications, photos, and pricing used in this tool are gathered from Kelley Blue Book data, information posted on Web sites of original equipment manufacturers (OEMs), and information provided by representatives of OEMs. Fuel economy figures come from the U.S Environmental Protection Agency (EPA). The vehicles and their specifications are updated as new models are released and/or changed. NREL conducts a comprehensive update of this database each fall based on new model year vehicles.

Caution: The AFDC recommends users check with their local dealers for more specific vehicle information before making purchasing decisions.

Vehicle Search - Heavy Duty

Methodology: Information about alternative fueled medium- and heavy-duty vehicles, engines, and hybrid propulsion systems is gathered from specifications posted on Web sites of original equipment manufacturers as well as information provided by vendor representatives. Vehicle specifications are updated as new models are released and/or updated. NREL conducts a comprehensive update of this database annually.