Prototype of self-driving vehicle, photo courtesy of Google.

Prototype of self-driving vehicle, photo courtesy of Google. 

Within four months Google has tripled its autonomous vehicle fleet from 23 to 73 cars, according to a report by CIO.

The California Department of Motor Vehicles (DMV) has issued licenses for 73 vehicles, up from 23 in May, according to CIO. State law stipulates that automakers looking to test self-driving cars and technology on public streets are required to get a permit for each vehicle from the DMV. Additionally, the drivers or testers of these vehicles need to be issued licenses for operating these cars, according to the report.

Google's autonomous vehicle fleet is composed of a small, two-seater prototype car and the Lexus RX450h SUV. With the addition of these 50 cars, in California alone, Google's licensed self-driving fleet now stands at 102 vehicles, according to the report. 

The second biggest autonomous fleet after Google is Tesla's, which has 12 licensed cars. Mercedes Benz has five autonomous cars its testing followed by Volkswagen, Delphi, Bosch, Nissan, and Cruise Automation, which have two cars each. BMW and Honda each have one autonomous car licensed in California, according the CIO report.