Alphabet Corporation’s self-driving car company Waymo recently announced its vehicles have driven more than 16 million kilometres (10 million miles) on public roads. The news comes ahead of the company preparing to launch a commercial ride-hailing service with fleets of autonomous vehicles.

Waymo’s testing rounds began with a handful of kilometres driven each day, exploding over the past few years. The company announced last Wednesday that its autonomous vehicles have driven more than 16 million kilometres on public roads in the United States. The company had logged almost 13 million kilometres in July and a little more than six million in November 2017. Simply put, Waymo’s testing rate is proliferating.

The self-driving cars contributing to the grand total were logged in 25 cities, prominently in Google’s hometown of Mountain View, California and in the greater Phoenix area where Waymo launched an early rider program to chauffeur passengers around the city. More than 400 early riders currently use the Waymo app and ride around in the company’s autonomous Chrysler Pacifica Hybrid minivans.

The progress Waymo has achieved on public roads can be put down to its investment in simulation, according to John Krafcik, Chief Executive Officer of the company. Extensive simulation testing will see the company hit more than 11 billion kilometres of virtual testing by the end of October.

The Waymo testing locations across the United States are rapidly increasing in number, currently standing at 25.

In a post on Medium elaborating on Waymo simulation testing, Krafcik wrote, “In simulation, we can recreate any encounter we have on the road and make situations even more challenging through ‘fuzzing’.” He further continued, “We can test new skills, refine existing ones, and practice extremely rare encounters, constantly challenging, verifying, and validating our software. We can learn exponentially through this combination of driving on public roads and simulation.”

Of course, merely spinning the odometer is not enough for autonomous cars. Companies like Cruise and Waymo with sizable fleets of self-driving cars have been challenged to develop self-driving cars that are capable of safely navigating complex urban environments, all the while fitting in with millions of human drivers on the public roads. It’s not always smooth sailing, for the cars are cautious by design (or software), sometimes causing traffic to rack up behind them. In such instances, a human driver is required to take manual control of the car to rectify the situation.

“Today, our cars are programmed to be cautious and courteous above all, because that’s the safest thing to do,” Krafcik wrote. “We’re working on striking the balance between this and being assertive as we master manoeuvres that are tough for everyone on the road. For example, merging lanes in fast-moving traffic requires a driver to be both assertive enough to complete the manoeuvre without causing others to brake and smooth enough to feel pleasant to our passengers.”

As is clear from the graph, Waymo is rapidly picking up the pace when it comes to testing its autonomous cars on public roads.

For now, Waymo cars are more circumspect and prefer taking the safer route even if that means adding a few more minutes to the trip, says Krafcik. The next 16 million kilometres will be devoted to making the service more convenient and efficient. Waymo is currently working to improve its routes, pick-ups, and drop-offs. Company engineers are also applying advanced artificial intelligence and new sensing systems developed in-house to tackle complex weather conditions like heavy rain and snow.