Motorists were stranded in Suswa on Tuesday as floodwaters cut off Narok-Mai Mahiu road.
The water flowed from the Mt Longonot area, where it had rained heavily. It does not rain much in Suswa.
Traffic snarl-ups on both sides of the road were the result, some motorists saying they had been waiting for more than one hour.
One Naomi Mwangi said she and other passengers from Nairobi had been stuck in their vehicle for an hour.
"Motorists are desperately waiting for the floodwaters to subside. This happened yet there hasn't been heavy rain in this area," she said, adding the floodwaters came with debris.
The section of the road that was cut off is the same one that was washed away after heavy rains in 2018.
In a statement, the Kenya National Highways Authority noted the affected section of the road was that near the standard gauge railway crossing at KM23 from Mai Mahiu, just before Suswa.
"[The section] has been overtopped by floods which caused heavy siltation," said Corporate Communication Assistant Director Charles Njogu.
Mr Njogu said the authority had mobilised two contractors to clear the siltation and restore traffic flow.
"KeNHA urges all motorists to be on high alert and not to attempt to cross any bridges or sections of the road that are overtopped by water," he said.