Transportation Sector Module - NEMS Documentation
August 2025
Introduction
The Transportation Demand Module (TDM) of the National Energy Modeling System (NEMS) is a computer-based energy demand module of the U.S. transportation sector. This report documents the objectives, analytical approach, and development of the NEMS TDM, and it catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and module source code.
This reference document provides a basic description of the NEMS TDM for analysts, users, and the public. It also facilitates continuity in model development that enables customers to undertake and analyze their own model enhancements, data updates, and parameter refinements.
Model summary
The NEMS TDM encompasses a series of semi-independent submodules and components that address different aspects of the transportation sector. This comprehensive module primarily provides projections of transportation energy demand by fuel type, including motor gasoline, distillate, jet fuel, and alternative fuels (such as electricity, compressed natural gas (CNG), and liquefied natural gas (LNG)). The current NEMS TDM projection period extends to the year 2050 and uses 1995 as the start year. Projections are generated through separate consideration of energy consumption within the various modes of transport: private and fleet light-duty vehicles (LDVs), aircraft, marine, rail, and truck freight. Other transportation demands such as mass transit, military, and recreational boating are also considered. This modular approach helps us effectively assess the impacts of policy initiatives, legislative requirements affecting individual modes of travel, and technological developments.
The module also projects selected intermediate values necessary to determine energy consumption. These elements include:
- Estimates of passenger travel demand by light-duty vehicles, air, and mass transit
- Estimates of the energy requirements to meet transportation demand
- Projections of vehicle stock and the penetration of new technologies
- Estimates of the demand for truck, rail, marine, and air freight transport that are linked to projections of industrial output, international trade, and energy supply
The NEMS TDM consists of four submodules that represent a variety of travel modes that are different in design and use but share the same purpose: to convey passengers and freight. The four submodules are Light-Duty Vehicle (LDV), Air Travel, Freight Transport (heavy truck, rail, and marine), and Miscellaneous Energy Demand (Figure 1). Each submodule is composed of one or more components, consistent with the methodological requirements of the sector and in proportion with the relative impact that sector has on overall transportation demand and energy use. A fifth (inactive) submodule exists in the TDM that can estimate certain air emissions from highway vehicles.
Scope and organization
Publication of this document is supported by Public Law 93-275, Federal Energy Administration Act of 1974, Section 57(B) (1) (as amended by Public Law 94-385, Energy Conservation and Production Act), which states in part:
...that adequate documentation for all statistical and forecast reports prepared...is made available to the public at the time of publication of such reports.
In particular, this report is designed to meet EIA’s model documentation standards established under these laws.
Model archival citation
This documentation refers to the NEMS TDM as archived for the Annual Energy Outlook 2025 (AEO2025).
The latest open-source NEMS code and input files are available at https://github.com/EIAgov/NEMS.
Model contact:
Transportation Energy Consumption and Efficiency Modeling
EIAInfoConsumption&EfficiencyOutlooks@eia.gov