A Spanish rail operator and an Italian engineering contractor are the latest to join forces with Texas Central Partners in the plan to build a bullet train between Dallas and Houston.

Texas Central announced Wednesday that Renfe will be its operator. The Spanish company runs 5,000 trains a day on 7,500 miles of tracks.

Before 2024 — the earliest that the 90-minute, Dallas-to-Houston passenger service is projected to begin — Renfe will have input on the design and construction of the Texas train and help develop Texas Central's operation and maintenance plans.

Renfe's first high-speed service connected Madrid and Seville in 1992. In 2007, it added a second high-speed line linking Madrid to Barcelona. Its more recent high-speed connections link Barcelona to France and Mecca to Medina in Saudi Arabia.

Last week, Dallas-based Texas Central announced that the construction and engineering firm Salini Impregilo will lead a civil construction consortium to build the line. Texas Central estimates the project's final costs at $12 billion to $15 billion.

Salini Impregilo has built over 4,000 miles of railway infrastructure around the world. The Italian company has worked in the U.S. since the 1980s and in 2016 merged with the U.S.-based Lane Construction Corp.

Texas' bullet train project gained Amtrak as a ticketing partner in May. Passengers will be able to book trips through Amtrak. The high-speed rail operator will also transport passengers between Union Station, which is Amtrak's Dallas endpoint, to the Dallas station between South Riverfront Boulevard and South Austin Street.

Texas Central will also provide similar shuttle service between the Amtrak endpoint and the former mall site it has chosen for a terminal in northwest Houston.

The high-speed rail project, with train speeds up to 200 mph, is undergoing environmental review from the Federal Railroad Administration. The agency hopes to finalize its environmental impact statement by Jan. 31. It hopes to make a decision on the project, based on the final report, by the end of August 2019.

Construction, which Texas Central believes would take five years, would start after the project receives environmental clearance.