The standard gauge railway route cutting through Nairobi National Park will be built in phases to reduce the impact on the environment and wildlife.
Kenya Railways managing director Atanus Maina made a case for the route on Thursday saying they were ready to convince the court.
Maina spoke at Embulmbul on Wednesday during the launch of the eight-kilometer Ngong tunnel that will cost Sh1.5 billion.
The launch signifies phase 2A of the project from Nairobi to Naivasha. Phase one was from Mombasa to Nairobi.
The entire Nairobi-Naivasha route will cost $1.483 billion and a commercial contract with China Communications and Construction Company has been signed for the construction of this phase. It is expected to be completed in June 2017.
Financing of the entire second phase will cost $ 5 billion (Sh507 billion), which will incorporate buying of wagons and building a port in Kisumu, with a timeline of four and a half years.
Maina said the launch did not mean an immediate start of construction, but was a way of informing the country of the government's direction.
The managing director said several issues were considered before the park option was considered.
These included property to be compensated for, impact of displacement on property and businesses and the cost of rerouting the railway line.
Maina further said it would be expensive to cut through Rift valley due to the terrain and added that the park route was the best economically and environmentally.
He also said the earmarked area will be fenced off to minimise interference with animals.
"We will build the bridge through the park in 18 months in three phases, with restoration being done after every phase," he added.
Maina also said Kenya Wildlife Service scientists and rangers will work closely with constructors to ensure maximum resource use and animal security.
The MD noted evacuation was not a viable option as it would be costly and have adverse effects on the environment.
But he said mitigation measures will include the construction of reflectors along the bridge. He said the government was considering constructing a bridge through the park at a cost of Sh50 billion as a show of concern for biodiversity.
Maina also said the National Land Commission will look into the amount of money needed for compensation once his office receives a report following an Environmental Impact Assessment study.
Transport PS Irungu Nyakera said the project had no implications as all seven options that were on the table terminated in Ngong.
A section of conservationists said the construction of the Nairobi-Naivasha railway through the park would drive away animals.
Concern also arose from several incidents of animals straying out of the park into residential areas.
Maina said last month that the SGR will cost taxpayers Sh2.02 billion more. The 120km route had been estimated to cost approximately Sh150 billion.