LOS ANGELES — U.S. officials say better planning by California might have prevented a bus from smashing into a truck whose driver had fallen asleep on a freeway last year. Thirteen people died.

The bus was carrying people back from a desert casino when it rear-ended the truck on Oct. 23, 2016 near Palm Springs. Traffic had been stopped briefly for utility work but the trucker didn’t start up again after traffic resumed.

In a synopsis Tuesday, the National Transportation Safety Board laid blame for the accident on the California Department of Transportation.

It said the agency should have required more Highway Patrol officers and some kind of advance warning for the traffic break.

The board also says both drivers were fatigued and had medical problems yet still had federal approval to drive.