Those who died were a married couple in their eighties and a 20-year-old man from Biberach, who was travelling in a different vehicle at around 1:15 am.
“A fog bank is likely the cause of the accident,” said a police spokesman.
Wreckage from the deadly pileup was scattered over more than 100 metres of road, leading to the closure of the B30 near Ulm-Donaustetten in both directions.
Three people suffered serious injuries and are being treated in nearby clinics.
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