Police are still figuring out what exactly happened Wednesday on fog-shrouded Interstate 5 that caused dozens of cars and trucks to crash, killing two drivers in separate incidents 8 miles apart and closing off sections of the freeway’s southbound lanes for much of the day.

Investigators are still “piecing everything together,” said Capt. Stephanie Bigman, of the Oregon State Police. The Oregon Department of Transportation called the pileup of some 60 vehicles, including 20 semitrucks, “an extremely challenging situation.”

Oregon State Police offered few details and provided no information on the first fatality, which happened at about 8 a.m. 14 miles north of Eugene.

Many drivers were going too fast, considering the foggy conditions, Bigman said. Drivers were temporarily rerouted to the northbound lanes.

Traffic that had backed up behind the morning’s initial crash was beginning to clear, and cars were passing through the scene when an unknown obstruction, possibly a tire in the road, created a minor fender-bender-like collision outside Halsey, Bigman said.

This led a Freightliner semitruck to pull to the right and stop in the slow lane. Another Freightliner truck crashed into it and caught on fire. The driver of the second freightliner, identified as Kirpal Singh, 63, of Yuba City, California, was killed, Oregon State Police said.

Two sedans rear-ended behind the semitruck crash, but the drivers were not injured.

The crashes each spanned more than a mile and closed the southbound lanes 16 miles north of the Beltline Highway intersection. Six of the involved semis were leaking fluids, police said.

ODOT said southbound I-5 south of Albany at state Highway 34 didn’t reopen until about 2:30 a.m.