California Partners for Advanced Transportation Technology

Rest areas are a countermeasure for fatigue; what role do they play in fatigue-related freeway collisions? The present study spatially evaluates fatigue collisions. In California, of 2,203,789 highway collisions recorded between 1995 and 2005, fatigue collisions accounted for 1.3% (‘strict’ definition of fatigue) and 9.7% (‘expanded’ definition). Collisions in the vicinity of rest areas were investigated using two different approaches: 1. 10-miles up/downstream of rest areas 2. Distance traveled from rest areas

Sample t-tests indicated that both fatigue and non-fatigue collisions decreased statistically significantly downstream of rest areas. Collisions due to fatigue tended to decrease immediately downstream of rest areas, then climbed after about 30 miles from rest areas, while non-fatigue collisions remained the same. Binomial tests confirmed that the percentage of fatigue collisions further than 30 miles from rest areas was significantly higher.

The study also compared ramps at rest areas to other ramps and found that trucks were the primary vehicle type involved in rest area ramp collisions. ‘Parked, parking’ movements caused the highest number of collisions on ramps at rest areas, compared with ‘proceeding straight’ movements for other ramps. The comparison revealed that some rest areas had too few parking spots. Finally, the study explored the growth of informal rest areas: shoulders frequented by truck drivers when other safe stopping opportunities do not exist. The study analyzed collision rates at informal rest area ramps and determined that the rates were higher, on average, than at other ramps. Analysis of fatigue-related collisions adjacent to informal rest areas provided mixed results regarding the efficacy of informal rest areas in reducing highway collisions. However, higher incidence of fatigue-related collisions at these locations supports the need for additional rest areas.