Transport along the Mombasa-Nairobi highway was paralysed for eight hours early Wednesday following a heavy traffic jam between Salama and the Machakos town turn-off.
The jam started building after three lorries collided near Malili township at 10 pm on Tuesday.
Seven people were injured, according to Makueni County Commissioner Mohammed Maalim.
They were taken for treatment at the Machakos County Referral Hospital.
By Wednesday morning, hundreds of motorists were stranded between Salama and the Machakos town turn-off.
Travellers heading to and from Mombasa spent the night in the cold.
The gridlock eased about eight hours later following intervention by traffic police, opening a floodgate of buses and trucks revving to recover time lost from sitting in the jam.