Traffic accidents involving large trucks in the United States have increased 47 percent according to the National Safety Council, and in 2021, these vehicles were responsible for nine percent of all vehicles involved in fatal crashes.

The NHSTA finds that microsleeps occur most frequently between midnight and 6 am, or in the late afternoon. At both times, people experience dips in the human body’s internal clock that regulates sleep.

The U.S. Centers for Disease Control and Prevention (CDC) says that most drowsy driving crashes or near misses occur between midnight and 2:00 am, between 4:00 and 6:00 am, or between 2 and 4 in the afternoon.

Accidents attributed to microsleeps frequently occur on rural roads and highways, and often involve only a single driver and no passengers. The trucks appear to have run off the road at a high rate of speed with no evidence of braking, according to the NHSTA.

Several studies worldwide have highlighted in particular the severity of collisions related to drowsy driving and their substantial risk of fatality.

A major risk here comes from microsleeps that lead to impaired cognitive and motor performance, including slower reaction times, decreased attention – even complete loss of consciousness.

Microsleep episodes can have a significant impact on driving performance and increase the likelihood of dozing off while driving, say the researchers at the Graduate School of Biomedical and Health Sciences at Hiroshima University.

In 2022, National Police Agency of Japan announced that falling asleep at the wheel was to be included in the same category of “forward inattention” as distraction, which has been the most frequent cause of fatal traffic accidents in the country for over 10 years.

Past research into typical microsleep behaviors has investigated one or more aspects of the problem such as eye closure or changes in pupil diameter.

But no study has yet performed an analysis that takes a holistic approach – considering the driver’s eye and mouth movements as well as the movements of his or her entire body and vehicle driving behavior.

Most studies have only considered driver performance during computer simulations. No research has yet looked at actual collisions of large trucks.

“In recent years, there has been an explosion in the use of dashcam video recorders,” said Hajime Kumagai, lead author of the paper and a specialist in sleep medicine with the Graduate School of Biomedical and Health Sciences at Hiroshima University.

“This means that a great many traffic accidents, and their possible relationship to episodes of microsleeping have been recorded. This inspired us to employ dashcam footage to investigate microsleep-related behaviors immediately prior to real-world truck collisions,” Kumagai said.

In total, the researchers reviewed 3,120 seconds of video footage from interior and exterior dashcams across 52 cases from truck collisions in Japan that had actually happened.

They analyzed the footage from one minute before the crash right up until the crash. In each incident, the person at the wheel had been a professional driver, and all crashes occurred on either urban roads or highways.

The footage was visually analyzed to evaluate any eye changes and microsleep-related activity including the driver’s actions to try to prevent falling asleep, behavioral signs of microsleep, and abnormal vehicle behavior.

The researchers concluded that the key signs of microsleep include behaviors that indicate a “creeping sleepiness” such as the absence of body movement, relaxation of the muscles such as back and neck muscles, as well as calves and quadriceps, eyes being half-closed, and closure of the eyes for one second or more.