This report presents the findings of an evaluation of the Department's need for a mode share estimating capability. The report documents the process to develop a standard/basic mathematical model for estimating transit riders in an urban area. The model was developed using data from San Antonio, Texas, and is operational using standard TRANPLAN programs on a personal computer using MS/DOS. This model will serve as the starting point for customizing a transit rider forecasting model for individual urban areas in Texas. The model developed is considered potentially applicable for home based work trips for mid-sized cities, smaller than Dallas and larger than 200,000. The model is a multinomial logic model based on traditional travel time and cost variables and treats travelers in four income stratifications. The current model structure and computer program estimate only transit riders but are adaptable to estimate High Occupancy Vehicle (HOV) users and the number of vehicles for different carpool sizes. The present model also does not include treatments for persons accessing transit by personal vehicles but could be readily expanded to do so. The model currently operates as a simplification of a nested model, so it can be easily modified to incorporate the above mentioned alternative modes in a nested model structure. This report describes the rationale for developing a mode share model for the Texas Department of Transportation. It then addresses the decision process that led to selection of the approach described above. Thereafter the data needs and process for obtaining and preparing those data are detailed, along with the procedures followed and results of estimating model coefficients. A users manual for the computer program, including data descriptions, is in the Appendix.