The Roadway Design Manual was developed by the Texas Department of Transportation to provide guidance in the geometric design of roadway facilities. It should be noted at the outset that this document is a guide containing geometric design recommendations and does not represent an absolute design requirement.
The Roadway Design Manual represents a synthesis of current information and operating practices related to the geometric design of roadway facilities. The fact that updated design values are presented in this document does not imply that existing facilities are unsafe. Nor should the publication of updated design guidelines mandate improvement projects. Infrastructure projects are by their nature long lived facilities. While design methodologies are constantly being improved, the implementation of these improvements typically occurs as projects are built, or rebuilt, in future undertakings.
Traditional roadway project development is expanding to include consideration of the impact on such stakeholders as non-facility users and the environment. This more complex approach must take into account both the individual project priorities and the relative priorities of the entire roadway system. Therefore, effective design needs to not only provide for beneficial design components, but also ultimately provide the most beneficial total roadway system of which each individual design project is only a part.
While much of the material in the Roadway Design Manual can be considered universal in most geometric design applications, there are many areas that are subjective and may need varying degrees of modification to fit local project conditions. The decision to use specific design guidance at a particular location should be made on the basis of an engineering study of the location, operational experience, and objective analysis. Thus, while this document provides guidance for the geometric design of highways and streets, it is not a substitute for engineering judgment. Further, while it is the intent that this document provide geometric design guidance, the Roadway Design Manual does not represent a legal requirement for roadway design.
Roadway design is a continually evolving process. As additional information becomes available through experience, research, and/or in-service evaluation, this guide will be updated to reflect current state-of-the-practice geometric design guidance for roadway facilities.