The San Bernardino County Transportation Authority has approved an $85 million project with a company founded by Elon Musk to bore a tunnel from the Rancho Cucamonga Metrolink station to Ontario International Airport.

The cost of the nearly 4-mile tunnel will be fraction of the expense of building an above-ground rail or light rail connection. It will take about four years to complete.

“Along with the possibility of higher-speed rail service into the Rancho Cucamonga station, the Loop project provides vital transit connectivity between Los Angeles County and San Bernardino County,” said Transit Authority President Frank J. Navarro, mayor of Colton.

He noted that the Rancho Cucamonga station is a hub for Metrolink’s heavily traveled San Bernardino Line, which is about to get another boost with development of the Arrow line between Redlands and San Bernardino.

“Creating new connections at Rancho Cucamonga is a win-win for commuters and cities across our region,” Navarro said.

Once the Redlands Passenger Rail Project is complete next spring, it will connect to the Rancho Cucamonga station. Once the tunnel is complete, possibly by 2025, Redlands residents will be able to reach the airport by train.

Boring was the only company to respond to a recent request for qualifications to build the tunnel, which will connect Metrolink’s busiest line with the nation’s fastest-growing airport three years running.

The subterranean transit system would shuttle thousands of passengers per day between the Rancho Cucamonga station and the airport using zero-emission vehicles.

The decision follows last month’s awarding of a contract to HNTB for construction management services.

“The Ontario Airport Loop project represents an innovative, cost-effective and sustainable approach in meeting the mobility needs of one of the most robust population and economic centers in the United States,” said Curt Hagman, chairman of the San Bernardino County Board of Supervisors.

It was Hagman’s vision for a tunneling project that led authority to investigate the feasibility of such a project.

The Boring Co., headquartered in the Los Angeles area, has built two tunnels nearly a mile long underneath the Las Vegas Convention Center.