Cost-effective roadway drainage design using economic analysis

A practical method for determining the road surface drainage system design with the theoretic Lowest Total Economic Cost (LTEC) is developed. The LTEC design determines the design rain which, when used in a rational-based design context, will yield the most economic choices of gutters, inlets, and laterals considering both construction costs and risk costs. The data needed to find the LTEC design rain are: the number of rains per year, the design gutter flow, duration of average rainfall, runoff coefficient, drainage area, inlet and lateral costs, capital recovery factor, and a traffic loss coefficient. A nomograph and data selection guidance are provided as design aids. Three case studies are presented in an appendix. The method, based on minimizing traffic delay costs, applies to freeways, arterials, and major collectors; local streets with low traffic may be excluded (A).