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Database Analysis 75 to visit the site of each accident, the data collection was performed in phases so the highway where the crash occurred would not be unduly blocked while all the data were collected. The CVSA Level 1 inspection was conducted at the repair facility, not at the accident scene. Advanced photographic techniques were used to enable the compilation of scaled schematics and scene measurement logs. The typical approach was to mark key points in the accident progression while the vehicles were present and then go back later and take more extensive measurements. In addi- tion, the accidents that were selected occurred close to the 17 locations where trained investiga- tors resided. No effort was made to require that the investigators travel great distances, thereby forcing long-term closure of the highway. Simply stated, the data collection and compilation were designed to minimize disruption yet, at the same time, collect data on many relevant parameters. 4.5.4 Data Compilation The data from interviews, photographs, accident scene measurements, and vehicle inspections were used to populate many of the parameters in the database. For example, the interviews with the carrier and driver were used to compile data on the driver's previous sleep interval, the hours of service recorded on the log, as well as data on the driver's mental and physical state. Similarly, the measurements taken at the scene were used to generate scaled schematics and the scene meas- urement log. Data from the interviews of the driver and carrier were used to identify the driver aggression and driver distraction factor number. Photographs and on-scene measurements were compiled into deformation logs to be placed in the database as deformation codes. 4.5.5 Accuracy and Completeness of Data Every effort was made to obtain a comprehensive set of data for more than 1,000 parameters. Many of the parameters were estimated from multiple sources of data and apparent or real incon- sistencies could be resolved normally, thereby producing a consistent dataset for each vehicle involved in the accident. In addition to the 43 tables in the database, there are numerous support- ing tables that define code numbers to be used instead of phrases or words. This increased the accuracy of entry among data compilers. In this regard, the LTCCS project generated a 512-page Analytical Users Manual to ensure that all of the parameters' codes were consistently entered into the database tables. The lengthiness of the manual is due primarily because a definition, source, cross reference, variable name, and attribute code ID was provided for each parameter. 4.5.6 Quality Control Extensive quality control checks were performed to ensure the accuracy of the data put into the database. The use of attribute codes that are defined in the Analytical Users Manual greatly enhances the quality of the data. Based on the manual, codes are used for most parameters and since the manual defines the meaning for each of the numerical codes, there is little room for ambiguity. This minimizes the inconsistencies in the dataset. 4.5.7 Interconnectivity with Other Databases It is not possible to connect the data in the LTCCS with other databases because the loca- tion and day of the month in which the accident occurred has been removed from the pub- lic version. The carrier is not named, the DOT number of the carrier is not given, and the vehicle registration number has been shortened. Any of these parameters would enable the datasets to be joined. There are only 57 crashes that involved hazardous material and, since HMIRS mainly reports spills, there are probably fewer than 10 crashes that might be reported in both datasets.