Pilot Collection and Evaluation of Head Kinematics in Stock Car Racing.

The goal of this work was to collect on-track driver head kinematics using instrumented mouthpieces and characterize environmental exposure to accelerations and vibrations. Six NASCAR drivers were instrumented with custom-fit mouthpieces to collect head kinematic data. Devices were deployed at four tracks during practice and testing environments and configured to collect approximately 11 min of linear acceleration and rotational velocity data at 200 Hz. This continuous data collection, combined with film review, allowed extraction of complete laps of data. In addition to typical data processing methods, a moving-point average was calculated and subtracted from the overall signal for both linear acceleration and rotational velocity to determine the environmental component of head motion. The current analysis focuses on 42 full laps of data collected at four data collection events. The number of laps per track ranged from 2 to 23. Linear acceleration magnitudes for all 42 laps ranged from 2.46 to 7.48 g and rotational velocity ranged from 1.25 to 3.35 rad/s. After subtracting the moving average, linear acceleration ranged from 0.92 to 5.45 g and rotational velocity ranged from 0.57 to 2.05 rad/s. This study has established the feasibility of using an instrumented mouthpiece to measure head kinematics in NASCAR and presented a technique for isolating head motion due to cornering acceleration from those due to short-term perturbations experienced by the driver.

Estimated crash injury risk and crash characteristics for motorsport drivers.

OBJECTIVE: Motorsport crash events are complex and driver restraint systems are unique to the motorsport environment. The National Association for Stock Car Auto Racing, Incorporated (NASCAR®) crash and medical datasets provide an opportunity to assess crash statistics and the relationship between crash characteristics and driver injury. Injury risk curves can estimate driver injury risk and can be developed using vehicle incident data recorder information as inputs. These relationships may provide guidance and insight for at-track emergency response, driver triage and treatment protocols. METHOD: Eight race seasons of crash and medical record data (including Association for the Advancement of Automotive Medicine Abbreviated Injury Scale (AIS) scores) from the Monster Energy NASCAR Cup Series & NASCAR Xfinity Series were processed and analyzed. Multiple logistic regression modeling was used to produce injury risk curves from longitudinal and lateral resultant change in velocity, resultant peak acceleration, principal direction of force and the number of impacts per incident. RESULTS: 2065 Unique IDR data files were matched with 246 cases of driver injury or sub-injury (severity below AIS 1) and 1819 no-injury cases. Multiple logistic regression modeling showed increasing resultant change in velocity, resultant peak acceleration and the number of impacts during a crash event all increase estimated driver injury risk. After accounting for the other predictors in the model, right lateral impacts were found to have a lower estimated injury risk. The model produced an Area Under the Receiver Operating Characteristics curve of 0.80. Across the eight race seasons in this study the overall average resultant change in velocity was 34.4 kph (21.4 mph) and the average resultant peak acceleration was 19.0 G for an average of 258 crashes per season. For 2011 through 2015, full time drivers experienced 134 times more crashes per mile traveled than passenger vehicles, but experienced 9.3 times fewer injuries per crash. CONCLUSION: Multiple logistic regression was used to estimate AIS 1+ injury only and AIS 1+ with sub-injury risk for motorsport drivers using motorsport-specific crash and medical record databases. The injury risk estimate models can provide future guidance and insight for at-track emergency medical response dispatch immediately following an on-track crash. These models may also inform future driver triage protocols and influence future expenditures on motorsports safety research.

Implications of head and neck restraint test repeatability for specification improvement.

Objective: Since 2005, National Association for Stock Car Auto Racing, Incorporated (NASCAR) drivers have been required to use a head and neck restraint system (HNR) that complies with SFI Foundation, Inc. (SFI) 38.1. The primary purpose of the HNR is to control and limit injurious neck loads and head kinematics during frontal and frontal oblique impacts. The SFI 38.1 performance specification was implemented to establish a uniform test procedure and minimum standard for the evaluation of HNRs using dynamic sled testing. The purpose of this study was to evaluate the repeatability of the current SFI 38.1 test setup and explore the effects of a polyester seat belt restraint system. Method: Eight sled tests were conducted using the SFI 38.1 sled test protocol with additional test setup constraints. Four 0° frontal tests and 4 30° right frontal (RF) oblique tests were conducted. The first 3 tests of each principal direction of force (PDOF) used nylon SFI 16.1 seat belt restraint assemblies. The fourth test of each PDOF used polyester SFI 16.6 seat belt restraint assemblies. A secondary data set (Lab B Data) was also supplied by the HNR manufacturer for further comparisons. The International Organization for Standardization (ISO) 18571 objective comparison method was used to quantify the repeatability of the anthropomorphic test device (ATD) resultant head, chest, and pelvis acceleration and upper neck axial force and flexion extension bending moment time histories across multiple tests. Results: Two data sets generated using the SFI 38.1 test protocol exhibited large variations in mean ISO scores of ATD channels. The 8 tests conducted with additional setup constraints had significantly lower mean ISO score coefficients of variation (CVs). The Lab B tests conducted within the current specification but without the additional test setup constraints had larger mean ISO score standard deviation and CV for all comparisons. Specifically, tests with the additional setup constraints had average CVs of 3.3 and 2.9% for the 0° and 30° RF orientations, respectively. Lab B tests had average CVs of 22.9 and 24.5%, respectively. Polyester seat belt comparisons had CVs of 5.3 and 6.2% for the 0° and 30° RF orientations, respectively. Conclusion: With the addition of common test setup constraints, which do not violate the specification, the SFI 38.1 test protocol produced a repeatable test process for determining performance capabilities of HNRs within a single sled lab. A limited study using polyester webbing seat belt assemblies versus the nylon material called for in SFI 38.1 indicates that the material likely has less effects on ATD upper neck axial force and flexion extension bending moment time histories than the test setup freedom currently available within the specification. The additional test setup constraints are discussed and were shown to improve ATD response repeatability for a given HNR.