Highway sites in ten States, where edgedrains had been retrofitted along the pavement edges, were instrumented to measure concurrent rainfall and edgedrain discharges, piezometric water levels, and soil moisture under the pavement and adjacent shoulders. Soil samples were also collected and their physical and hydraulic properties measured; all sites were found to have relatively low permeabilities. Fifty selected rainfall-runoff events were analyzed to assess the amount of infiltration reaching the pavement subgrades, amounts and timing of edgedrain discharges, and the manner of water movement beneath the pavement. The data indicate that retrofitting longitudinal edgedrains to an existing highway provides a sink to collect water draining laterally off the pavement surface as well as water reaching them from the subgrade voids and channels. The tight, low permeability subgrade material found to exist at all ten sites precluded ready, lateral drainage with or without edgedrains. The edgedrain outlets then serve to short-circuit the combined flow through the highway shoulders. The low permeabilities were also confirmed by the transducer data because piezometric water levels beneath the pavements were generally slow to recede. The data obtained indicate that most of the lateral subgrade movement of water is through voids and channels that develop under the pavements. In a sense, "the horse is already out of the barn" if the deterioration of the highway has reached this state. If highway restoration, as well as new construction, includes providing a permeable subbase as well as edgedrains, the two together should prove the most efficient in restoring the highway. In addition to providing data as to the effectiveness of edgedrains, this study also developed and tested instrumentation and techniques for studying pavement drainage. A dual tipping bucket gage proved most effective in measuring concurrently rainfall and edgedrain discharges. Pressure transducers were effective in measuring piezometric water levels beneath the pavements. Data loggers proved effective in not only recording all data but could be programmed to operate the sensors only and to the extent needed. The need to acquire core samples of the subgrade material and analyze for physical and hydraulic properties was emphasized.