A Waymo executive announced on Tuesday that the company's self-driving car fleet would reach 7 million miles of testing this week.

"We've amassed close to 7 million miles—we'll hit 7 million miles this week," said Shaun Stewart, Waymo's chief business development officer, at the Innovfest Unbound conference in Singapore.

What makes this truly remarkable is that Waymo announced its last milestone—6 million miles—less than a month ago. Waymo CTO Dmitri Dolgov made that announcement at the Google I/O conference on May 8.

Dolgov didn't specify exactly when Waymo reached the 6 million-mile mark. So the last million miles might have actually taken a bit more than a month to rack up. Still, Waymo's pace of testing is clearly accelerating as the company gears up to launch its driverless taxi service later this year.

Waymo made this chart back in February to mark 5 million miles of testing. It shows that it took Waymo (then Google) more than a year to get from 1 million to 2 million miles. Then it took about six months each to get to 3 million and 4 million miles. Waymo logged its next million miles in about three months.

Now, three and a half months later, the company has racked up 2 million additional miles. And while Waymo made a big deal out of its early milestones, the last two have been low-key affairs, with executives casually dropping the new statistics in the middle of larger talks about Waymo's plans.

No one else in the industry is close to matching the scale of Waymo's testing. Uber had logged roughly 3 million miles before it was forced to suspend testing in March due to a fatal crash in Tempe, Arizona. GM's Cruise drove only 131,000 miles in California between December 2016 and November 2017—the most recent period for which we have data.

Of course, miles on their own don't prove anything about vehicle safety, as Uber's deadly crash demonstrates. In an October blog post, Cruise CEO Kyle Vogt argued that testing in dense, chaotic San Francisco allows Cruise to learn more from each mile of testing than rivals like Waymo that predominantly test in suburban areas.

But Waymo's accelerated testing program is just one of several signs that the Alphabet company is investing heavily to maintain its early lead in driverless vehicle technology.

Last month, Waymo announced that it had ordered 62,000 Chrysler Pacifica minivans, on top of the 20,000 Jaguar I-PACE order Waymo announced in March. Waymo's most recent order is by far the largest such order in the driverless car business. The closest comparison is to Uber's order of 24,000 cars from Volvo. But with Uber's testing now grounded, it's not clear if Uber will be ready to use those vehicles when Volvo is ready to start delivering them next year.

Waymo says it's planning to launch a commercial driverless taxi service in the Phoenix area before the end of the year.