A U.S. study said one in 10 road accidents (10 percent) may have been due to driving while drowsy, a much higher rate than what was previously expected.

“Drowsy driving is a bigger traffic safety issue than federal estimates show. Drivers who don’t get enough sleep are putting everyone on the road at risk,” said David Yang, the executive director of the AAA Foundation for Traffic Safety which conducted the study.

The United States group suggested that the current statistics on road crashes caused by driving drowsily could be much higher, from 1 to 2 percent, and could even be as much as 10 percent.

In the study, the researchers included 4,593 drivers, with emphasis on more younger and older drivers, recruited in six U.S. cities to take part in the Second Strategic Highway Research Program Naturalistic Driving Study (SHRP 2 NDS).

The participants’ driving and in-vehicle behaviours were monitored using cameras and other vehicle collection equipment for several months from October 2010 to December 2013.

The researchers assessed the drivers’ drowsiness level using the PERCLOS, which measures the length of time a driver’s eyes are opened given a defined interval.

“PERCLOS has been shown to be predictive of drowsiness, lapses in attention, and increased variability in lane position,” noted the researchers.

To assess whether an accident is caused by drowsiness, data reductionists studied the final three minutes of ‘road accident’ videos to see if the drivers’ eyes were closed (80 percent shut).

A driver is considered drowsy if the eyes are closed in 12 percent or more of the video frames.

Approximately 31 percent of the crashes were severe or moderately severe, while 69 percent were not police-reported.

“Overall, the driver was classified as drowsy in 9.5 percent of all crashes. The proportion of crashes that involved drowsiness varied significantly in relation to lighting conditions, with drowsiness evident in over three times the proportion of crashes in darkness as in daylight,” noted the researchers.

While differences in age, sex and crash severity did not account much, much of the drowsiness-related accident occurred in darkness.

“Driver drowsiness is an under-reported traffic safety problem, largely because its role in crashes is typically difficult to ascertain,” they added.

The experts then recommend that drivers should get at least seven hours of sleep to prevent road accidents, as not having so is linked with elevated road crash rates. MIMS