The Saudi Arabian government awarded $22.5bn in contracts to build a driverless metro rail system in the capital Riyadh.
The project, which will involve six rail lines extending 110 miles and carrying electric, driverless trains, is the world's largest public transport system currently under development, Saudi officials said.
The contracts went to three foreign-led consortia with US construction giant Bechtel heading a group which won a $9.45bn contract to build two lines, the government announced. Its partners include Germany's Siemens and US-based AECOM.
A consortium led by Spain's Fomento de Construcciones y Contratas, and including France's Alstom Transport and South Korea's Samsung C&T, won a $7.82bn contract for three lines.
Italy's Ansaldo STS heads a group that won a $5.21bn order. Its partners include Canadian firm Bombardier and India's Larsen & Toubro.
Design work will start immediately and construction will begin in the first quarter of 2014, the government said, with the project expected to be completed in 2019.
The project "will be a major driver of employment and economic development," said Ibrahim Bin Muhammad Al Sultan, head of the government body overseeing the project. "It will also help to reduce traffic congestion and improve air quality."
Last August the government approved a $16.5bn plan to modernise the transport system in the holy city of Mecca, including creating a bus network and a metro system and it is also building several other rail systems, including a 2,750 km line running from Riyadh to near the northern border with Jordan.
Saudi officials said Riyadh's population was projected to grow from 6 million to over 8 million in the next 10 years, making the metro vital to ease congestion and pollution in the capital's streets.
In addition to raising living standards, the government says it wants to upgrade the country's infrastructure to help the economy diversify beyond oil, making it less vulnerable to any future plunge of global oil prices.
The contracts may provide a welcome financial boost to some Western construction companies struggling with slow economic growth in their home markets and state austerity policies in debt-choked Europe.