According to the United States Department of Transportation (USDOT), more than 3.1 billion tons of hazardous materials (HazMat) are shipped within the country annually. This averages to about 800,000 individual shipments of hazardous materials per day, of which 300,000 are shipments of petroleum/flammable-combustible liquids. This paper presents a temporal trend study (1995-2004) of 1,850 HazMat incidents occurring through the transportation of flammable-combustible liquids. The study was centered about HazMat shipments originating within five states (California, Illinois, Iowa, New Jersey, Texas) chosen for their geographic variations in size and location. The main objective of this study is to conduct a frequency analysis of HazMat incident as a function of distance between origin and incident location. Procedures for this study entailed compiling a sample of HazMat road incidents originating within the selected states and generating the great-circle distance from their originating location to sites of incident. The distance between origin and incident locations were attained through great-circle calculations because data compilation did not allow for the identification of specific routes utilized in commodity transport. Key findings of the analysis illustrated a bimodal distribution of incident frequency as a function of the great-circle log distance. The first mode presented an average distance of incident which was short haul in classification. The second mode presented an average distance of incident which was long-haul in classification. The study also addressed incidents as they occurred within primary phases within transportation. For all phases, incidents occurred at average distances which are long haul in classification. Time series forecasting suggests continuing trends in HazMat incidents. Findings of this study speculate fatigue to be a contributing factor for incident occurrences. This requires that more research be carried out on various aspects of flammable-combustible liquids such as hours-of-service regulations, fatigue and incident reporting.