Fog was blamed for several accidents involving 42 vehicles in southeast Bexar County on Thursday morning.
According to the Bexar County Sheriff's Office, the 13 separate accidents happened on the northbound and southbound lanes of Interstate 37 between Hardy Road and Loop 410.
Injuries were reported, but none of them were life-threatening, sheriff's officials said.
Motorists tried to get around the pileups by taking back roads, but they still ran into road blocks.
"Back over the way here it just stopped again, and so we just started sneaking round, and we got tied up again, and just stopped," said Dave Derrick, who got caught in traffic. It's just going to be a mess. We're trying to get on down to Pleasanton, but I don't think we're gonna make it today."
Dustin Miller said he was pulling a trailer with his pickup over a hill when all of sudden the motorists in front of him slammed their brakes. Miller couldn't stop in time.
"I jack-knifed," Miller said. "There was a semi that jack-knifed. Several semis went off the road. Very lucky."
Deputies at the scene reported visibility at the scene to be about 100 feet or less.
Until noon, Southbound I-37 was shut down at Loop 410. Northbound I-37 at Loop 1604 was closed for several hours but was later reopened.