HSRL hopes to build eight miles of railway alongside the M25 motorway from the west end of the Terminal 5 station to improve rail access to Heathrow Airport from the south.
The project would link Heathrow Airport with trains from Guildford, Farnborough, Woking and London Waterloo. The cost of the project is estimated at £1.2bn.
The value of Aecom’s investment in the project was not disclosed, nor the terms, except that Aecom is now involved in developing the project.
HSRL chair Baroness Jo Valentine said: “Coming from such an internationally respected organisation as Aecom, this funding represents a significant vote of confidence in our project.
“The funding from Aecom will be used for developing the project to the next stage, which will include further stakeholder engagement – vital given that our proposed new rail connection will benefit many communities in the region. This is a significant step forward for the Heathrow Southern Railway, which will be fully financed privately, at no net cost to the taxpayers, and could be operational by as early as 2024.”