Apple’s autonomous driving program is one of the worst kept secrets in Silicon Valley but little is known about it as the company has remained relatively tight-lipped.

That silence continues but documents from the California Department of Motor Vehicles show Apple’s fleet of autonomous vehicles has grown to 55. This means the company has the second largest fleet of autonomous vehicles in the state as it’s only behind Cruise Automation which has 104 autonomous vehicles which are being tested by GM.

Apple’s fleet is even larger than Waymo’s but not by much. The documents show the autonomous driving division of Alphabet has permits for 51 vehicles.

While Apple has the second largest fleet of autonomous vehicles in the state, they don’t have that many safety drivers. USA Today says the company has just 83 drivers compared to the 407 and 339 that GM and Waymo have.

The growth of Apple’s autonomous driving fleet is notable as MacReports says the company originally started with just three vehicles. The fleet eventually expanded to 45 vehicles before climbing to the current number of 55.

While Apple appears to be significantly ramping up their autonomous driving efforts, it’s interesting to note the company hasn’t filed an application to test vehicles without a driver. However, that could just be a matter of time as the driverless permit process just opened up last month.

The constant rumors sounding Apple make it hard to separate fact from fiction, but the company received a permit to test autonomous vehicles in California a little over a year ago. Public records have also shown some of Apple’s prototypes are based on the Lexus RX 450h and fitted with a Logitech steering wheel.

Apple CEO Tim Cook has also confirmed the existence of the program as he has previously stated “We are very focused on autonomous systems. We do have a large project going and are making a big investment in this.” He went on described autonomy as the “mother of all AI projects.”