Elon Musk’s the Boring Company seems to have come some ways from selling hats. In a tweet Wednesday, the billionaire entrepreneur announced his tunneling venture will bid to build an express service between Chicago downtown and the O’Hare International Airport.

Chicago Infrastructure Trust, started by the city’s Mayor Rahm Emanuel, announced on its website it was opening bids for private companies to "design, build, finance, operate and maintain the OES [O’Hare Express System] Project," which it says "will improve transportation between O’Hare International Airport and downtown Chicago by providing faster, more direct, and more reliable service."

Musk explained briefly, in reply to some Twitter users, that the "high-speed Loop" he mentioned in his announcement referred to a transport system similar to his Hyperloop concept, but without the need for vacuum tubes for the electric pods to move in.

The Hyperloop concept — which he gave away to anyone who wanted it and which has since been used by other companies to design their own transport systems — basically envisages transporting people and goods in pods moving at incredible speeds, of up to hundreds of miles an hour, on rails within tubes that have vacuum inside them to remove friction from everything, including air. This would drastically reduce the energy required to keep the pods moving.

Musk said the Loop system would not need to have vacuum tubes, since it is for relatively short rides and can therefore work without getting rid of air friction. And that while it would also use pods, it would not necessarily need rails for the pods to move on.

Despite the friction offered by air, the Loop system would likely complete its Chicago downtown to O’Hare journey in under 20 minutes, since that is the goal of the OES Project, according to the city’s Deputy Mayor Bob Rivkin. He also said the city would look at options both above and below the ground, so long as the service operated at least once every 15 minutes, at a cost lower than taxis, Chicago Sun Times reported.

Before Musk had made the announcement about the Boring Company making a bid, Rivkins had expressed hope for exactly that to happen.

"We hope Elon Musk and either builders of hyper-loops and other innovative technologies will respond," Rivkin said.

Emanuel and his staff have been in talks with Musk for several months about a tunnel connecting Chicago downtown to the airport.

Oh, about the Boring Company hats, Musk announced Nov. 21 over $300,000 worth of them had been sold.