The accident that closed a section of Rockville Pike in Bethesda for nearly eight hours Wednesday night occurred after a southbound Toyota Tacoma pick-up truck crossed the median of Rockville Pike and collided with the front end of a northbound Metrobus, killing the truck driver, Montgomery County police said Thursday.

What caused the truck driver, who was alone in the truck, to cross the road remains under investigation, police said. Police identified the truck driver as Nkonou Ayaovi Edorh, 49, of the 14200 block of Georgia Avenue in Silver Spring.

The bus driver was one of two seriously injured in the accident that saw a total of eight people aboard the bus taken to hospitals. The bus driver is Lennitta L Bryant, 41, of the 3300 block of Weeping Willow Court in Silver Spring, police said. Metro said she is a 13-year veteran driver who was operating a bus headed to Lake Forest Mall. She remained hospitalized Friday.

 The accident occurred at 4:16 p.m., police said, on Rockville Pike near Alta Vista Road but closed a section until nearly midnight between Cedar Lane and Pooks Hill Road while crash detectives investigated.

 Investigators are asking anyone who witnessed the accident to contact them. Callers may remain anonymous. The Collision Reconstruction Unit can be reached at 301-840-2435.