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Remove Restrictions on SES

The Subway Environment Simulation (SES) Computer Program, Version 4.1 is an important tool for mass transit systems and tunnels. This document requests the United States Government remove the restrictions on the SES program and associated documentation. Submitting my name indicates I personally support this request. I understand its capabilities and believe the SES program should become publicly available again.


The SES program analyzes tunnel environments. It is a one-dimensional airflow and thermodynamic solver, as schematically shown in Figure 1. As explained in the User’s Manual, “SES … is a designer-oriented tool which provides estimates of airflows, temperatures, and humidity, as well as air conditioning requirements, for both operating and proposed multiple-track subway systems.” The program can also be used for road tunnels, passenger rail, and freight rail.

Research and development for SES started in the 1960s with the United States Government distributing the program and source code in the 1980s and 1990s. Over the years, this program became the industry standard and is still the most widely used one-dimensional tunnel model.


Post 9/11, the United States Government started restricting the source code and program's distribution to new users because of perceived security issues. No official documentation explaining the restrictions appears readily accessible. Meanwhile, organizations use, distribute, or sell programs with capabilities derived from the SES's research and source code.

Sample Data

The SES 4.1 solver does not contain any data except for general engineering constants and conversion factors. The program was distributed with two sample input text files that do not represent real-world systems.

Other Programs

Below is a list of other solvers available. Reviewing academic literature suggests that all these programs are derivatives of the source code of SES 4.1 (except ThermoTun). Of the examples below, the most broadly available and used is a commercial software package, IDA.

  1. IDA Tunnel is described at This program's brochure advertises, “Import and SI conversion of SES input files”. The company EQUA licenses this software for one year for about 11,000 USD.

  2. STESS, “Subway Thermal Environment Simulation Software”. The academic paper explains this program is based on the source code of SES.

  3. SSES is created in Iran appears to be based on SES 4.1

  4. ThermoTun described at

Open-Source Development

Removing restrictions gives all companies fair access to the program, regardless of past access. Also, the industry can benefit from program improvements from open-source development. The industry already benefits from the open-source development of other engineering programs, such as the Fire Dynamic Simulator by the National Institute of Standards and Technology (NIST).

Supporting Comments

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