Flow smoothing in sanitary sewers was studied to determine under what conditions the resulting higher flow capacities can be economically obtained. Conservative assumptions were made in this preliminary design and economics study to provide a severe test for the cost effectiveness of the concept. In many situations, flow smoothing is an attractive alternative when compared to relief pipe installation. Circumstances which favor flow smoothing are high interest rates, high peak-to-average flow ratios, low pipe slopes, small diameters, and low design depths of flow. Flow smoothing is strongly favored where earthen construction can be used. (Author)