Head acceleration events in stock car auto racing: motivating and assessing track changes

Between the 2023 and 2024 NASCAR racing seasons, a track configuration change to a section of the Watkins Glen International track, known as the bus stop, was made in response to head acceleration data measured in the 2023 season. The objective of this study was to evaluate the effect of this change on head acceleration events (HAEs) among drivers.

Mouthpiece (MP) sensor data was collected and analyzed from eight NASCAR Cup Series drivers in 2023 and 2024 at the Watkins Glen race. Each MP was tightly coupled to the upper dentition and collected linear and rotational head kinematics using a 4 g single-axis trigger threshold. All HAEs were visually verified as racing events (i.e., during the race, not associated with a crash). HAEs associated with the bus stop were identified using timing and scoring data and analyzed. Peak linear acceleration (PLA), rotational acceleration (PRA), and rotational velocity (PRV) were calculated for each HAE. The number of HAEs and HAEs per lap were calculated for each driver-race. Linear mixed effects models and Poisson models were used to determine significant changes year to year. Mixed effects models were used to evaluate the relationship between head surround gap and kinematic metrics.

Overall, there were 693 HAEs in 2023; and 333 HAEs in 2024 across the eight drivers. Track changes to the bus stop from 2023 to 2024 reduced the mean events/lap by ∼53% (0.96 to 0.45, respectively). Mean resultant PLA, PRA, and PRV decreased by 6%, 27%, and 10%, respectively. Across individual drivers, decreases in event rate ranged from 25% to 98% for drivers instrumented in both seasons. Individually, mean PLA decreased by as much as 20%, PRA as much as 41%, and PRV as much as 25%.

Drivers were exposed to a substantially lower HAE rate and significantly lower magnitude HAEs at the bus stop in 2024 compared to 2023. This shows that the track change between 2023 and 2024 in the Watkins Glen bus stop reduced driver head acceleration exposure. This work demonstrates the value of biomechanics data to motivate changes in track configuration and improve driver safety based on biomechanics.