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10 CHAPTER 3 Study Approach 3.1 General The data collection plan presented in this chapter covers the data elements requiring supplemental field data collection To accomplish the study objectives, the following major and reconstruction. tasks were undertaken in this study: Identify data needs 3.3 Data Collection Alternatives Evaluate data collection alternatives Three basic alternatives were considered for the data col- Develop data collection protocol lection effort in the current study: Conduct supplemental data collection, manual review, and reconstruction Create relational database 1. New data collection system Incorporate data from previous studies into database 2. Prospective special study under the NASS CDS program 3. Retrospective supplemental data collection for existing Details of these tasks are presented in the following sections. NASS CDS cases The database was then analyzed to address the study objectives and the results are presented in Chapter 4. Finally, a proposed More detailed discussions of these alternatives are presented implementation plan for a long-term data collection effort below. was developed and outlined in Chapter 5. 3.3.1 New Data Collection 3.2 Data Needs The first alternative was to establish a totally new data col- The primary goal to be achieved under the current study is lection system. The major activities required in the setup of a to identify the distribution of impact conditions associated new data collection system at multiple sites include, but are with serious injury and fatal ran-off-road accidents, includ- not limited to, the following: ing speed, angle, and vehicle orientation at impact. It is hoped that this information can then be used to select impact con- Establish data collection teams. This would require hiring ditions to be used in full-scale crash testing of roadside hard- of new personnel, establishing and furnishing the offices, ware. In order to address this issue, the needed data elements purchasing the necessary equipment for conducting crash were identified and are listed in Table 1. The data elements investigation, etc. are categorized as available from: Train investigators in the basics of in-depth level crash investigation. The newly hired investigators would need to 1. Basic NASS CDS data. These data elements are already be trained extensively to acquire the required level of exper- available as part of the basic CDS data. tise, including both classroom and on-the-job training. This 2. Supplemental field data collection. These data elements training would need to be extensive and comparable to what will require field data collection. is used with the NASS CDS program. 3. Reconstruction. These data elements will require recon- Develop procedures for obtaining authorization to collect struction of the crashes. medical records.

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11 Table 1. Data needs for current study. Variable Availability Case Screening Criteria Area type - PSU 1 Crash type - Single-vehicle, ran-off-road crashes 1 Vehicle type - Passenger vehicles only 1 Completeness of data on key variables 1 Injury severity - Serious and fatal injury 1 Variables of Primary Interest: Encroachment conditions at point of departure - Action prior to leaving travelway 1 - Speed 3 - Angle 3 Pre-impact vehicle trajectory - Vehicle path 3 - Maximum lateral extent of encroachment 3 - Total longitudinal distance 3 General impact data - Impact sequence 1 - Object struck 1 - Rollover occurrence 1 - Post-impact trajectory 3 Impact conditions first harmful event - Impact speed 3 - Impact angle 3 - Vehicle orientation 3 Impact conditions most harmful event - Impact speed 3 - Impact angle 3 - Vehicle orientation 3 Driver action - Evasive action 1 - Steering vehicle path 3 - Braking 3 Controlling Variables: Highway type - Functional class 2 - Roadway type 1 - Speed limit 1 Travelway characteristics - Number of lanes 2 - Lane width 2 - Horizontal curvature - Point of departure and maximum 2 - Vertical grade - Point of departure and maximum 2 Roadside characteristics - Shoulder type and width 2 - Roadside slopes widths and rates of slopes 2 - Median type, width, and slope 2 Traffic characteristics - ADT 2 - Percent truck 2 Struck object characteristics - Object type 2 - Impact performance 3 Vehicle characteristics - Type 1 - Make and model 1 - Curb weight 1 - Vehicle damage 1 - Occupant compartment deformation and intrusion 1 Highest occupant injury severity - Abbreviated Injury Scale (AIS) 1 - Police Injury Code (PIC) 1 EDR data 1 (continued on next page)

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12 Table 1. (Continued). Variable Availability Variables of Secondary Interest: Time - Day of week 1 - Time of day 1 Environmental conditions - Light 1 - Weather 1 *Legends for Data Availability: 1. Existing NASS CDS data 2. Supplemental field data collection 3. Reconstruction Establish cooperation with local agencies. This would tive in nature (i.e., data would be collected on new crashes) include law enforcement agencies for the notification sys- and could be within sample (i.e., only crashes that are already tem, vehicle towing and repair facilities for access to the sampled under the NASS CDS program would be eligible) involved vehicles, hospitals and clinics for medical records/ or outside of sample (i.e., all crashes are eligible). Again, information on injury severity, and transportation agen- this alternative is not viable for this study due to time and cies for highway-related information. funding constraints. First, it will take a minimum of 12 to Establish quality control procedures. To assure proper data 18 months to set up a special study under the NASS CDS pro- collection in terms of validity and accuracy, appropriate gram. Second, this assumes that the NASS CDS program can quality control procedures would need to be established, accommodate a new special study on short notice, which is similar to the Zone Centers in the NASS program. rarely the case. Because the CDS system itself requires a cer- tain number of crashes to be investigated and the researchers After the data collection system was established, additional can handle only so many crashes (1 1/2 to 2 cases per week per activities would be required to establish the specific data col- researcher), the ability of the system to conduct special studies lection effort, including: is limited. This limitation can be overcome by hiring new investigators specifically to handle the special study, such as in Develop data collection protocol. The field forms and the case of the special study on large-truck crash causation. accompanying coding and instruction manuals, data col- The addition of new investigators is not as time consuming lection procedures, data submission processes, and qual- or costly as establishing new data collection teams, but would ity control procedures would have to be developed for the still require more time and funding than available for the cur- specific data collection effort. rent study. However, this alternative remains viable for a long- Train investigators in specific data collection effort. The term data collection effort. investigators would have to be trained in the details of the specific data collection effort. This would be in addition to 3.3.3 Retrospective Supplemental the basic training mentioned above. Data Collection Conduct pilot study. A pilot study would have to be con- ducted to work out any unforeseen problems in the data The third alternative was to conduct a retrospective study collection protocol. using previously investigated NASS CDS cases. This approach was similar to that successfully used in NCHRP Project 17-11 It is evident from the above discussion that the alternative and the FHWA Rollover Study. In those studies, single-vehicle, of establishing a new data collection system was not a viable ran-off-road crashes were selected from 1997 through 1999 option for this study due to funding constraints. The startup NASS CDS cases. Since NASS CDS cases are oriented toward costs would be prohibitive for such a short-term data collec- vehicle crashworthiness and occupant injury and lack details tion effort. However, this remains a viable alternative for a pertaining to the highway and roadside characteristics, sup- long-term data collection effort. plemental field data collection and manual review and recon- struction of the cases were used to fill in the data gaps. A total of 559 cases were sampled under these studies. 3.3.2 Prospective NASS CDS Special Study This approach can be implemented within a short period The second alternative was to establish a special study under of time since it involves only existing NASS CDS cases. Sup- the NASS CDS program. The special study would be prospec- plemental field data collection protocol and manual review