The purpose of this research effort was to investigate the impact of rainfall, at varying levels of intensity, on freeway capacity and operating speeds. Findings were derived from traffic and weather data collected in the Hampton Roads region of Virginia. Light rain (0.01 to 0.25 inches per hour) decreases freeway capacity by 4 to 10 percent. Heavy rain (0.25 inches per hour or greater) decreases freeway capacity by 25 to 30 percent. The presence of rain, regardless of intensity, results in approximately a 3 to 5 percent average decrease in operating speed. The findings indicated that the impact of rain is more significant than currently reported in the Highway Capacity Manual.