In response to major derailments involving hazardous materials cars, the Federal Railroad Administration (FRA) initiated the review of the consequences of hazardous materials car placement in a train consist. The review and analysis consisted of six task items: 1) review of accident trends and regulations; 2) an analysis of hazardous materials compatibility; 3) railroad operational constraints; 4) a cost/benefit analysis; 5) recommendations; and, 6) preparation of a final report. A review of the 1982-1985 Railroad Accident/Incident Reporting System (RAIRS) data showed the rear quarter to be statistically the 'safest' location in a mainline freight train. Also, the top 101 hazardous commodities (by volume movement) plus fuming nitric acid were analyzed for chemical incompatibility, a total of 5,151 binary combinations. Consequence-based and risk-based rankings were established. Calculations established a post-derailment separation distance of 40 meters minimum to prevent mixing of incompatible chemicals. It was noted that mixing of hazmat materials was not cited in any NTSB accident report as a specific problem.