Major roads will be closed from today evening ahead of Pope Francis' arrival in Nairobi.
Roads to be affected include Uhuru Highway, Kenyatta Avenue, Haile Selassie Avenue, Harambee Avenue and University Way.
Police said Mombasa Road through Uhuru Highway to State House will be temporarily blocked this evening.
Nairobi head of police Japheth Koome said this will allow President Uhuru Kenyatta and his team to move to the airport to welcome the pontiff.
Mr Koome said Uhuru Highway will tomorrow morning be blocked from Bunyala Road roundabout to the Museum Hill overpass to allow a special mass take place at the University of Nairobi graduation square.
"We expect up to a million people at the grounds and hence the need to block motorists. Pedestrians will be allowed to walk to the venue," Koome said.
He said motorists coming from Upper Hill, including Ngong Road and Kawangware, would not be allowed to cross Uhuru Highway to the central business district.
Koome said the venue would be open to the public from 4.30am tomorrow.
President Kenyatta has declared tomorrow a public holiday because of the mass to be held then.
Motorists driving from Westlands will be diverted to the CBD at the Museum Hill overpass while those from Thika Road will access the CBD without disruption. However, he said, some might be blocked at Globe Cinema roundabout and Ojijo Road. Those from Jogoo Road will be able to access the CBD.
Police advised motorists from Mombasa Road to park their vehicles at Syokimau and Imara Daima railway stations, Capital Centre, Highway Secondary and Nyayo Stadium and either take a train or walk to town.
Those from Thika Road he advised to park at Moi Avenue Primary School, St Peters Claver's while those from Parklands and Westlands can park at Aga Khan Primary School.
Motorists from Ngong Road and Upper Hill were encouraged to park at Don Bosco Church, Upper Hill Secondary School, St Georges Secondary School, near the National Housing Insurance Fund (NHIF) building and the Kenya National Library.
"Public service vehicles from Ngong Road are advised to turn at NHIF. They will not be allowed into the CBD," said Koome.
He made the remarks when he met security chiefs among them Nairobi County Co-ordinator Njoroge Ndirangu and Traffic Commander Edward Mwamburi in Nairobi to finalise plans for the event.
Tomorrow evening, sections of Limuru Road to UN headquarters will be closed, police said. The Pope will be addressing an inter-religious group at the Unep offices.
On Friday, sections of Kabaserian, Waiyaki Way, Manyani Road and roads around Kangemi will be closed for a short while as the Pope will be visiting the area.
Thika Road will also be closed for some time as the Pope and his entourage move to Kasarani Stadium for a youth event.
Koome asked motorists to co-operate with police officers who will be on the ground giving instructions. "We have deployed a good number of officers who will be on the road to ensure your safety," he said.
The Catholic leader will be in Nairobi for three days.
