The year 1989 marked the completion of a major segment of FHWA's environmental research program. More than 15 years of water quality research have been supported by FHWA and state highway agencies. Since the early 1970s, FHWA has supported a four-phase research program in non-point-source pollution from highway runoff. Phase 1 identified the constituents of highway runoff and developed a data base of highway runoff quality and quantity. Phase 2 identified the sources and migration patterns of highway runoff constituents and further developed the Phase 1 data base. Phase 3 results indicated that highway facilities with low-to-medium average daily traffic (less than 30,000 vehicles per day) exhibited minimal impact on receiving waters. Phase 4 developed a new predictive procedure for estimating the pollutant loadings from highway sources, and identified practical, effective, and implementable mitigation measures to reduce or eliminate the impacts from highway runoff. The need for further environmental research is discussed.