The section of Harambee Avenue between Parliament and Continental House will be closed for the next six months.
That part of the road will be inaccessible until the end of May next year as Parliament constructs a tunnel to link its premises on both sides of the road.
In a notice in the Nation on Monday, the Nairobi County Government urged motorists to use alternative routes following the closure, which was effected on November 6.
The tunnel will cost Sh110 million, Parliament said, and will provide access to the basement parking of the 27-storey building being put up next to Continental House.
Mr Jeremiah Nyegenye, the secretary of the Parliamentary Service Commission, said the tunnel is mainly meant for access of vehicles to the basement parking in the building under construction.
He added: “The building when completed will provide parking for 400 vehicles.
"Due to the security requirement of checking vehicles accessing the building, vehicles stopping on Harambee Avenue would result in serious congestion and it was therefore necessary to develop the access to the basement parking.”
Motorists going to the new building will drive into Parliament and then drive through the tunnel into the first basement level.
Mr Nyegenye said the tunnel would reduce traffic in the area once the new building, budgeted to cost Sh5.8 billion, is complete.
The Senate clerk said the idea of having a tunnel was first mooted by the ninth Parliament, when Continental House was acquired.
The building has offices for MPs and the rooms in which they hold committee meetings as well as a restaurant and a gym.