The scope covers the construction of three tunnels, at a total length of 3.3 kilometres, which will run beneath the existing Riyadh Air Base in the centre of the capital. Two tunnels will measure 800 metres in length, with the third measuring 1.7km.

The tunnels will extend two major road arteries under the airport: Aruba street, which runs from east to west, and Abu Baker road, which runs north to south.

The project is designed to alleviate traffic congestion within the capital. Currently, in the absence of a through road, traffic in the area is forced to go around the air base, which covers an area of about 5 square kilometres.

The contract will also cover associated works such as the construction of groundwater and storm water pumping stations.

Prospective bidders include the local Shibh al-Jazira Contracting, Saudi Oger, Al-Mabani and Saudi Binladin Group.

The deadline for bids was originally set for 15 October, but was recently extended by five weeks to 18 November.

“The tender was issued around Eid, which gave us little time to put together a bid for the work,” says one contractor considering making a bid. “A month was nowhere near enough, so we needed the extra time.”

The Riyadh Air Base is used for military and royal flights. Commercial flights arrive and depart from King Khalid International airport.