**Background:** Shift-work-related fatigue is associated with safety, health, and performance impairments, with 12-hour night shifts being particularly problematic. Despite national work-hour regulations for physicians, nurses remain unprotected by national work-hour policy. The American Nursing Association has emphasized reducing nurse fatigue due to associations with errors affecting patient care, occupational injury, burnout, and long-term disease risk. Previous research using self-reported measures and driving logs has shown increased adverse driving events following night shifts, but no simulation studies had been conducted specifically with nurse participants. This study aimed to provide quantitative estimates of the impact of 12-hour day versus night shifts on nurses' driving safety risks.
**Methods:** The study employed a mixed repeated-measures (post-shift vs. time off), between-groups (12 h day vs. 12 h night shift) design. Ninety-four nurses (49 night shift, 44 day shift; one participant excluded from analysis) were recruited from a local medical center. Participants came to the lab on two occasions: once immediately after their third consecutive 12-hour shift (on-duty condition) and once on their third consecutive day off (off-duty condition), with order randomized. Day-shift nurses were tested at approximately 21:00 and night-shift nurses at approximately 09:00 to control for circadian factors. Testing occurred in the Washington State University Sleep and Performance Research Center using high-fidelity MPRI PatrolSim IV driving simulators. The driving scenario was a 20-minute rural drive with unexpected events. Primary outcomes were lane deviation, braking latency, braking violence (force applied to braking divided by time to maximum braking), and collisions. Multi-level modeling with adjustments for multiple comparisons was used for analysis.
**Key Results:** Night shift nurses had significantly greater lane deviation than day shift nurses (f = 5.40; df = 1, 1588; p < 0.05), supporting the primary hypothesis. Although there was a trend toward greater lane deviation during on-duty versus off-duty conditions, this did not reach significance (f = 2.45, df = 11,588; p = 0.12). Night shift nurses had significantly greater braking violence than day shift nurses (f = 20.12, df = 1, 840; p < 0.001), indicating a greater startle response regardless of on- or off-duty status. No significant differences in braking latency were observed. Collisions occurred in 10% of on-duty drives versus 9% of off-duty drives (not significant), and in 7% of day shift drives versus 11% of night shift drives (not significant at the 0.05 alpha threshold). No significant interactions between shift type and shift duty were observed for any outcome, indicating night shift nurses were at greater risk even after days off.
**Clinical Implications:** These findings provide objective, quantifiable evidence that nurses working 12-hour night shifts are at significantly increased risk for driving collisions compared to day shift nurses, as demonstrated by greater lane deviation and more violent braking responses. Notably, the elevated risk persisted even after three consecutive days off, suggesting a potential chronic effect of night shift work on driving safety. The results support national healthcare organization concerns about fatigue as a hazard for healthcare worker safety and justify the need for workplace policies to mitigate these risks. Recommended interventions include education on sleep hygiene, fatigue countermeasures (light therapy, caffeine, exercise), on-duty napping programs, matching nurses' chronotypes to shifts, and providing rideshare services for post-shift transportation, particularly for night shift nurses who are most at risk.