3TC is a consortium of multiple firms, which includes Stantec as the design professional.
The new contract covers the construction of a third track that will be placed within the existing LIRR on a 9.8mi-long segment of the main line between Floral Park and Hicksville.
The segment is one of the more heavily utilised sections of the line, serving more than 250 trains on weekdays.
It is used by roughly 40% of all LIRR customers.
The construction of the third track is anticipated to reduce congestion during peak times, as well as enable the rail operator to carry out emergency repairs without impacting regular services.
After completion, the LIRR expansion project will also offer faster journeys for commuters and reduce the frequency of delays.
MTA chairman Joseph Lhota said: “Upon its completion, this modernisation initiative will provide faster commuting with a more reliable network, and will allow us to keep the railroad in a state-of-good-repair.
“All too often, major delays on the LIRR are tied to incidents along this corridor.
“With this investment, Long Islanders and New York City residents alike will be able to avoid the crippling and cascading delays that affect the entire network.”
MTA Capital Construction has also awarded a competitive, $99.996m request for proposal (RFP) contract to the Arup – Jacobs joint venture (JV) for project management consulting services relating to the third track project.
The total cost of the development, with the two contracts and other associated expenses, is estimated to be approximately $2.6bn.
The contractors are scheduled to start work on the initiative from the beginning of next year and the project is expected to be completed by late-2022.