The "Manual on Uniform Traffic Control Devices" and the "Standard Highway Signs Book" have been developed around the use of the FHWA Standard Alphabets in an all-uppercase format for use on conventional road guide signs. These publications include a complex series of dimensions and tables based on specific legend sizes for various standard signs; however, the standards do not include guidance for the myriad different layouts that are developed to address unique local conditions. The mathematical relationship of the legend to the border, border size, and line spacing and the mathematical relationship of the graphics to the panel are not based on any standard criteria; as a result, sign layouts are not consistent for signs of similar types. In this paper, a recommendation is made to simplify the formatting of conventional road guide signs. Although these signs are used for many purposes, a similarity in their general design principles provides a basis for a common system of sign layout that relates all of the various dimensions (e.g., border width, word and graphic spacing, and line spacing) to a single common element, the height of the letters used on the sign (for mixed-cased applications, the height of the initial capital letter). To accommodate the use of mixed-case words, a series of proportion-based grid formats has been developed. This series of layout grids is based on the value X, where X is the size of the initial capital letter of the primary legend. The proposed formatting is called the proportional grid system.