The association of schedule characteristics of heavy vehicle drivers with continuous eye-blink parameters of drowsiness

Study objectives: While drowsiness contributes to 20% of heavy vehicle crashes, the impact of work schedules on heavy vehicle driver (HVD) drowsiness is unclear. This study explored the impact of work schedules on drowsiness (measured by infrared oculography) in HVDs. 

Method: Work and drowsiness monitoring (Optalert, Australia) of ten HVDs, aged 37–62 years collected nearly 2430 h of work and 1068 h of oculography data during four weeks of naturalistic drives. Drowsiness events were defined as a John's Drowsiness Scores ≥ 2.6. Nine HVDs slept for 5.82 ± 1.37 h during five weeks of actigraphy. Association of driving schedule characteristics and drivers’ continuous eye-blink parameters were observed using logistic and mixed linear regression analyses. 

Results: Combination of time of day (10 pm- 2 am), shift start time (2 pm-3 pm), hours into the shift (16–21 h), break duration (7–9 h), and sleep time (<6 h) increased the likelihood of drowsiness events when controlling for other covariates. A combination of night times (6 pm to 2 am), 18 to 21 h into the shift, shift start times (6 am to 7 am), shifts lengths (8 to15 h) and break times (<7 to 9 h) increased the hourly rate of drowsiness significantly when adjusting for other covariates. 

Conclusions: The combination of prolonged work hours, night-time drives, early-morning shift starts and short breaks increase drowsiness rates in HVDs. Large datasets are needed to examine the interplay between sleep time, consecutive shifts and shift order and type with this combination.