Traffic has built up on Thika Road at Allsops after a contractor closed inner lanes of the highway to build an overpass.
The new exchange is expected to ease traffic at the junction of the busy way and Outer Ring Road.
Only two lanes of the main highway are currently in use for the road that handles hundreds of thousands of vehicles per day.
On Monday, some commuters on their way to work in Nairobi CBD were caught up in the snarl-up that stretched to Garden City Mall.
“Major jam on Thika Road from Allsops ingoing, caused by the lanes being reduced to 2 due to the construction,” read a tweet by Ma3route, which gives traffic updates to motorists.
Mr Njoroge Muchiri, who used the road, tweeted: “Allsops the cause of Thika Road traffic jam up to Githurai.”
The contractor is doing an interchange for the Outer-Ring Road that connects Thika and Mombasa roads.
Outer Ring was opened more than a year ago but traffic on the road has worsened, forcing Kenya Urban Roads Authority (Kura) to build a new exchange linking it to Thika Road.
There have also been several design afterthoughts on Outer-Ring Road— including the ongoing construction of a middle road on the space between the two sides of the road after street lights had been completed in Umoja.
In a notice issued early this year, Kura said the junction that links Outer Ring Road to Thika Road would be constructed for about three months.
For the duration of the project, the Thika Road bound traffic from Outer-Ring Road will connect from the right-hand side service road of the highway and then turn to the right onto the underpass at Survey of Kenya while airport-bound traffic from the Central Business District will connect to Outer-Ring Road using the Garden City overpass.
The overpass will ease traffic snarl-ups at the junction near the GSU headquarters.