Yahoo Japan has invested 490 million yen ($4.4 million) into SB Drive, an autonomous vehicle joint venture established in Japan last year by telecom giant SoftBank and research company Advanced Smart Mobility. SoftBank also extended its investment by another 190 million yen ($1.7 million), taking its total stake to 510 million yen ($4.6 million) following its share purchase last April, according to a statement issued earlier today.

The ultimate aim of SB Drive is to “commercialize smart mobility services that utilize self-driving technologies,” with a specific focus on community services such as designated bus routes between towns and cities. In its short lifespan so far, SB Drive has been carrying out trials of a fixed-route bus service, as well as a truck convoy for freight transportation. In late 2018, SB Drive says it plans to kick off its first fully autonomous driving trials on public roads.

Advanced Smart Mobility is a research offshoot from the University of Tokyo’s ITS Center, and SB Drive seeks to combine those smarts with SoftBank’s communications infrastructure. Yahoo Japan was previously announced as a partner in the initiative, but today marks its first official investment in the venture.

Yahoo Japan is the result of a joint venture itself, set up in 1996 by Yahoo and SoftBank. Though Verizon is currently in the process of acquiring Yahoo in a recently amended multi-billion dollar deal, this doesn’t directly impact Yahoo Japan, which will continue to operate as a standalone publicly traded company in Japan, as it has done for two decades.

Though it appears SB Drive is focusing primarily on public transport for now, other players in Japan are doubling down on efforts to keep apace with autonomous vehicle advances elsewhere in the world. Nissan is expected to launch the country’s first self-driving car later this year, while the government is committed to making self-driving taxis a prominent feature of Tokyo in time for the Olympics in 2020. The success of this endeavor will likely hinge on Robot Taxi, a collaborative effort between robotics company ZMP and DeNA, which provides a range of online and mobile services.

As a result of the latest share allocation, SB Drive now has around 1 billion yen ($9 million) invested, with SoftBank holding a 51.1 percent stake, while Yahoo Japan holds 48.6 percent, and Advanced Smart Mobility claims 0.3 percent.

The self-driving vehicle revolution is entering overdrive, with Intel recently shelling out $15.3 billion to acquire Mobileye, a computer vision firm specializing in autonomous cars. And last month, California-based Embark launched its self-driving truck tech to ease driver fatigue on long highways.

Sign up for Funding Daily: Get the latest news in your inbox every weekday.