After months of testing and millions of miles developing self-driving vehicle technology, Waymo has officially launched the country's first commercial autonomous ride-share service.

The company's Waymo One program will give customers rides in self-driving vehicles 24 hours a day. Initially, the service will be limited to cities surrounding Phoenix, including Tempe, Mesa and Chandler.

While there may be many potential customers who want to ride in an autonomous vehicle, the Waymo One service will initially be offered to a limited number of people. Those customers will include hundreds of people in the Phoenix area who were test users of the Waymo self-driving vehicle fleet that has been in development since April 2017.

"Self-driving technology is new to many, so we're proceeding carefully with the comfort and convenience of our riders in mind," said Waymo CEO John Krafcik. One example of Waymo taking a cautious approach rolling out its ride-share service is the company's use of safety drivers to supervise the rides, at least initially. In addition, the company's app and consoles in the Waymo One vehicles will allow riders to instantly connect with support agents who can assist riders with questions.

Alphabet's Waymo One marks the start of the race by automakers, tech companies and other firms to launch autonomous ride-share services. General Motors subsidiary Cruise plans to launch a similar service using self-driving vehicles next year.

What's driving the competition? The pursuit of greater profits. Studies of have shown the biggest cost for ride-share operations is the expense of paying a driver. General Motors estimates it costs ride -share companies more than $3 per mile in San Francisco. However, GM believes that cost could drop to roughly $1 per mile by 2025 with driverless vehicles in ride-share fleets.

Waymo has said it expects the cost to consumers for using Waymo One to be competitive with Uber, Lyft and other ride-hailing services.