The closure is set to continue until Monday, August 11, 2025.
It affects the Southwestern loop connecting A8 (Waiyaki Way) to the Southern bypass, at the intersection with the Western bypass.
The works, the agency, said involves the reconstruction of ramps, loops, and slip roads.
As part of the traffic management plan, the agency said vehicles from A8 heading to the Southern Bypass are being diverted to E1507 Kikuyu-Link Road at the Sigona Golf Club junction.
Motorists coming from Nakuru toward the Southern bypass will use the newly constructed Southeastern loop.
They can alternatively use a temporary diversion along the Southern bypass median.
Those travelling from the Western bypass to A8 (Waiyaki Way) are required to use the Muguku interchange and then proceed through the Kikuyu-link road to rejoin A8 at the Sigona golf club junction.
The agency's Director General Kung'u Ndungu also used the opportunity to urge road users to observe road signs.
"KeNHA advises motorists to follow the traffic management plan, project road signs, and cooperate with police and traffic marshals on site," Ndungu said.
