A sleep-deprived driver operating a motorcoach during early morning hours on a California highway caused a crash that killed four of the 24 passengers, the National Transportation Safety Board said in a report released this week.

“Here’s yet another fatal crash involving both a motorcoach carrier with a starkly evident history of safety problems and a severely fatigued driver,” said NTSB Chairman Robert L. Sumwalt. “It’s time that the Federal Motor Carrier Safety Administration (FMCSA) move more aggressively to keep these unsafe carriers off American roadways.”

A motorcoach operated by Fresno-based Autobuses Coordinados USA Inc., traveling from Los Angeles to Modesto on State Route 99, drifted out of its travel lanes, striking a barrier system and a highway signpost shortly after 3 a.m., Aug. 2, 2016, near Livingston, Calif. The crash forces resulted in the signpost entering the passenger compartment and tearing through almost the entire length of the vehicle. The surviving passengers received serious-to-minor injuries.

Investigators determined the driver, who was seriously injured, had only about five hours of opportunity for sleep in the 40 hours preceding the crash, leaving him in a state of “acute sleep loss” at the time of the crash. There were no tire marks or other indication the driver took any action to avoid the barrier after the motorcoach drifted out of its travel lane.

According to FMCSA records Autobuses Coordinados vehicles failed eight of 29 federal inspections in just under two years, pushing its out-of-service rate to 38%, almost five times greater than the national average of 8%.

After determining that inadequate safety practices of Autobuses Coordinados and the FMCSA’s lack of oversight of contributed to the crash, the NTSB called on the FMCSA to change its motor carrier safety rating system to ensure carriers with serious safety issues either mitigate those risks or be placed out of service.

In its report the NTSB cited two 2011 motorcoach crashes it investigated that also occurred during early morning hours involving sleep-deprived drivers — a 15-fatality crash in New York City at 5:38 a.m., and a four-fatality crash in Doswell, Va., at 4:55 a.m. — and said those driving during early morning hours, when human performance is often degraded, present a unique risk to safety. To address that risk the NTSB reiterated an earlier recommendation that the FMCSA incorporate scientifically based fatigue mitigation strategies into hours-of-service regulations for passenger-carrying drivers operating overnight.

The NTSB also determined that the guardrail, which did not prevent the motorcoach from colliding with the signpost, and was not designed to do so, contributed to the severity of the crash.

The NTSB also issued two new recommendations aimed at developing risk-based guidelines to determine where high-performance barrier systems should be installed to shield heavy vehicles, such as motorcoaches, from roadside obstacles and hazards.