The commuter exposure modeling package consists of two documents. The User's Guide describes program execution and provides the user with the information needed to run the program. This document is a detailed description of the model methodology and code. This document is for users needing more detailed information about the model than is given in the User's Guide. It contains a detailed description of the model methodology and code that covers topics such as the definition of the modeling approach, traffic, emissions, and dispersion modeling, and commuter exposure statistics. A section describing and defining the symbols used in the computer code is also included. Detailed flowcharts of all of the model subroutines comprise another section. Finally, a discussion of the dimensions of arrays in the code and how to change dimensions is presented.