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92 Hazardous Materials Transportation Incident Data for Root Cause Analysis Sample crash information was input and stored in the Hazmat Accident Database, a specially designed database that enabled the aforementioned information sources concerning a particular crash to be assembled into as complete a record as possible. This included characteristics describ- ing the crash event, as well as the accuracy of the information itself. Extensive database protocols and quality control checks were employed to accomplish this objective. Once database develop- ment was complete, analyses were performed on the database for the purpose of providing infor- mation that might support the development of more rigorous hazmat truck safety policy. 4.9.2 Adding Explanatory Variables to the Hazmat Accident Database For the Hazmat Accident Database, the Hazmat Serious Truck Crash Project added a num- ber of fields designed to capture the actions of the vehicle(s) before the crash. In addition, fields were added to provide more detail on the type and quantity of the hazardous materials, hazmat packaging, infrastructure, and such driver characteristics as age and experience. Explanatory variables are crash characteristics that help explain cause and effect. Table 4-28 shows the five types of explanatory variables. The crash analysis process involved associating explanatory variables with impacts to determine how vehicle, driver, packaging, infrastructure, and situational characteristics influence crash occurrences in general, as well as those that result in spills. Appendix E (available on the TRB website at www.TRB.org by searching for HMCRP Report 1) describes selected analytical results from the project. 4.9.3 Crash Records Selection Of the approximately 2,000 hazmat crashes in the MCMIS database in 2002 (out of a total 105,000 records), the Hazmat Serious Truck Crash Project selected about one-half of the hazmat crashes for a more in-depth analysis. These records were primarily selected on a random basis, with the exception that less common accidents involving hazmat Classes 1, 4, 5, 6, and 7 were all selected to obtain a large enough population. Before performing data analysis, weighting factors were applied to compensate for the non-random aspects of the selection. Table 4-29 shows the hazmat crash classes selected for more detailed analysis. 4.9.4 Populating Records and Improving Data Quality After the records were imported into the Hazmat Accident Database, HMIRS data were used to both fill in data for fields not included in MCMIS and for quality checking the existing data. Because the HMIRS fields are more fully populated, any fields in the database that were com- mon to HMIRS and MCMIS were overwritten by the HMIRS information. The remaining HMIRS information was also incorporated into the database. Table 4-28. Explanatory variables used in the Hazmat Accident Database. Vehicle Driver Packaging Infrastructure Situational Configuration Age Package Type Road Surface Pre-Crash Condition Cargo Body Experience Quantity Shipped Road Condition Dangerous Event GVW Condition Quantity Lost Road Type Vehicle Speed Age (Cargo Tank) Trafficway Impact Location Rollover Protection Access Control Primary Reason Inspection History Speed Limit Accident Type Design Specification No. of Lanes Weather Condition