This digest presents key findings of National Cooperative Highway Research Program (NCHRP) Project 1-34, "Performance of Subsurface Pavement Drainage." It provides a useful summary of the effects of subsurface pavement drainage features on the performance of asphalt concrete (AC) and portland cement concrete (PCC) pavements developed from an extensive body of field project data obtained through 1998. Further, it will serve as a good basis of reference for similar results now being obtained from Special Pavement Studies 1 and 2 in the Long-Term Pavement Performance program. Thus, the digest will be of particular interest to engineers in the public and private sectors with responsibility for the design, construction, and rehabilitation of AC and PCC pavements. The digest is organized in the following sections: Background; Controversy Over Subsurface Drainage; Key Questions Addressed; Data Collected in Project 1-34 and Data Obtained from Other Sources; Analyses Conducted; Effects of Subsurface Drainage on Flexible Pavements; Effects of Subsurface Drainage on Rigid Pavements; Findings for Retrofitted Edgedrains; Cost-Effectiveness Findings; Discussion of Findings; and Limitations of Findings. Two tables are included showing, respectively, a summary of AC pavement sections analyzed and a summary of PCC pavement sections analyzed. This report may be accessed by Internet users at http://trb.org/publications/nchrp/nchrp_rrd_268.pdf
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