Bridj, a data-driven, venture-backed bus startup based in Boston, said Sunday it's winding down operations after a deal with a "major car company" fell through.

"Today, our incredible journey unexpectedly ends," said CEO Matt George in a post on Medium on Sunday evening. "After three years and millions of passenger miles as the largest operation of our kind in the country, Bridj is winding down."

Bridj said it's shutting down for good.

The company, which operated in Boston, Kansas City, Washington, D.C. and Austin, Texas and describes itself as a "pop-up" urban transportation system, officially shut down last Friday. The company had been in talks with the Massachusetts Bay Transportation Authority to offer late-night service to passengers.

George said in the post that Bridj had been pursuing "a deal with a major car company who promised a close date for a sizable transaction in lieu of a traditional venture capital funding round. The close date timeline extended from weeks to months, as they sought to gain the appropriate internal approvals that we (and they) thought were already in place."

But that deal ultimately failed, he said.

"And with that, we say goodbye," George continued. "We say goodbye to you, our 50 exceptional team members, our customers, and our partners all over the world. We also say goodbye to the promise of what could have been."

In an email to the Business Journal, George declined to disclose the name of the car company with which it was in talks. Bridj had teamed up with Ford Motor Co. (NYSE: F), however, in its expansion into Kansas City.

The company had raised about $10 million in investor funding from investors including FKA Atlas (now known as Accomplice), NextView Ventures and Suffolk Equity.