Silicon Valley-based has become the latest firm offering rides to the public in a self-driving car.

Alphabet Inc.'s self-driving unit Waymo has been running its Early Riders trial in Phoenix, Arizona for several months and plans to start a commercial service later this year. Aptiv's nuTonomy has also been running a trial with its own self-driving cars in parts of Boston and Singapore.'s trial kicked off in Frisco, Texas on Monday. While Waymo's self-driving cars cover about 100 square miles of Phoenix, at present is covering only a few routes in Frisco, for example between the HALL Park office complex and The Star stadium complex.'s self-driving technology has been fitted to donor Nissan NV200 vans and is at Level 4 capability. The vehicle can handle all situations within a mapped area, a practice known as geo-fencing. says its routes include crossing six lanes of traffic, navigating parking lots, and pulling over and leaving the curb to pick up and drop off passengers on-demand. External monitors on the vehicle explain to other drivers and pedestrians what actions it is undertaking. has been using a combination of real-world and simulated driving to train its artificial intelligence system at the heart of its self-driving technology. Simulations are important as it allows the engineers to test for situations that they may not encounter in the real world, like piloting around cars and reacting to a car that's run a red light. Toyota is going a step further and building a test site where its self-driving cars can learn to handle emergency maneuvers.

For's trial, there is still a human behind the wheel to take over in case of emergency. Eventually the company wants to replace the human backup driver with a chaperone of sorts to educate riders on the technology, but ultimately it will remove its the chaperone too and rely on a remote team for monitoring.