Juniper says Google is the most promising player in driverless cars (Photo: Google)

There will be almost 20 million fully autonomous or self-driving vehicles on the world's roads by 2025, according to a new study.

The outlook, which adheres to the more optimistic scenarios of some automakers, was presented by Juniper Research, which also said consumer adoption is set to take off as early as 2021.

The researchers sketched out a path to autonomous driving that foresees increased use of advanced driver assistance features such as adaptive cruise control and automated braking. These will help prepare drivers for the change, they said.

Despite the relatively short time frame, Juniper noted that the auto industry has work to do on the commercial front. "A discernible monetization strategy has not become evident," the research firm said in a press release.

In a ranking of what it called "the top 5 most promising players in the driverless car sector," Juniper said Google took the number 1 spot, followed by Volvo Cars, Daimler, Tesla and Apple. The lineup took into account factors such as the number of live trials conducted, technology development, the scale and scope of companies' projects and their future market potential.

Google, the report said, was seen as the most promising player because the internet search group has been at the forefront of autonomous-driving trials in recent years.