The Narok-Mai Mahiu road has been rendered impassable after floodwaters cut off the section on Monday evening.
The police in Narok asked motorists to use alternative routes until the situation is rectified.
Dozens of travellers were stranded for a better part of Monday following the disruption of traffic flow.
The situation resulted into a gridlock on both sides of the road.
On March 19, Kenya National Highway Authority barred heavy commercial vehicles from using the road.
This was after the section, which sunk owing to volcanic activity, was cut off a second time.
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On Saturday, the Nairobi-Mombasa road was cut off at the Sultan Hamud bridge following a heavy downpour.
Video footage showed motorists in traffic and buses stuck in large pools of water. A river in the area burst its banks.
"Use Machakos-Wote-Makindu Road until the water level subsides," Charles Njogu, a KeNHA official, said.
