Motorists plying the Maai Mahiu-Narok route spent the night in the cold after a section of the road was washed away by floods.
Truck driver Julius Kibe, who witnessed the phenomenon, said he had parked his vehicle a few meters from a section of the road that was washed away.
He said that a pickup driver escaped death narrowly while driving on the damaged section.
“We watched in horror as the vehicle hung precariously. Quick action by a breakdown crew saved the driver,” Mr Kibe said.
He said the water level had gone down considerably when the road caved in at around 8.30pm.
Mr Kibe, who was ferrying sand to Nairobi, was Wednesday still stuck next to the washed out part as engineers embarked on major repairs.
Infrastructure Principal Secretary Julius Korir, who inspected the section, said the road had “inherent” weaknesses.
He said repairs would most likely take close to 48 hours, with light vehicles allowed to use a section of the road.
“We are repairing the damaged section. We expect normal traffic flow within the next 48 hours,” he said.
Mr Korir said that the busy road had been “totally cut off”, with a fissure extending more than three kilometres upstream and 200 metres on the opposite end.
“When we go back to the office, we shall definitely look for a lasting solution to avoid disruptions in future,” he said.
He hinted at a possible redesign of the road as it is prone to damage during rainy seasons.
Kenya National Highways Authority (KeNHA) director general Peter Mundinia, who was among the high-ranking officials who visited the scene, blamed geology for the damage.
“The washout has been occasioned by heavy rains and geological cracks,” he said.
He said the Rift Valley region is prone to volcanic activities, adding that repairs would include filling up the fault line.
A diversion had eased traffic flow, he said, adding that the road leads to the world famous Maasai Mara Game Reserve.
“The repairs will involve filling up the damaged section and restoring the road to its original status,” Mr Mundinia said.
Police and safety marshals were manning the area round the clock to ensure safety of motorists, especially at night.
Some youth helped passengers ferry luggage at a fee from one end of the damaged road to the other where they resumed their journey.
Former President Kibaki commissioned the Maai Mahiu-Narok Road on August 26, 2011. The road links Nairobi with western Kenya.
Closure of the highway is likely to adversely affect motorists and tourists travelling to Narok, Maasai Mara Reserve and western Kenya.