Silvercar's fleet of A4 sedans is available at 15 different airport and urban locations in North America.

Audi has moved to acquire Silvercar, a small rental car company that exclusively offers a fleet of A4 sedans.

Audi invested $28 million in the Austin-based startup in 2015, though the companies have collaborated since 2012 under the "Audi mobility," Silvercar and Dealerware brands.

Most of Silvercar's rental fleet is available at airports, ranging from Las Vegas to Chicago O'Hare. In New York, customers can also pick up one of the A4s in Manhattan or several locations in Brooklyn.

"Audi and Silvercar share a vision for the future of transportation," says Audi of America CFO Matt Carpenter. "This acquisition enables Audi to move forward with a progressive partner and continue our technology leadership into the next era of mobility."

Audi plans to use Silvercar's technology platform to manage 'mobility' services in both corporate and retail environments.