Feature: Uber's self-driving cars pick up passengers in Arizona, face challenges ahead

"Thank you for choosing self-driving car! Welcome aboard!" A silver Volvo XC90 with a fast spinning radar on the top stopped at the entrance of a student dorm near the campus of Arizona State University in Tempe.

After almost two months of dispute and a long distance relocation from California to Arizona, Uber started its pilot program in Tempe, the U.S. state of Arizona, in February.

The newly released Uber experiment self-driving car, with Nate and Ruben -- the two technicians "supervising" it -- on board, picked up its first customer in the early morning on Feb. 26, a typical quiet Sunday morning.

After the passenger got seated in the back row, he saw an iPad installed in the center of the back row showing his name and the route to the destination on it.

Above the map, there were four circles, showing four signs, which were "Seat belts fastened", "3 rider maximum", "No destination changes", and " Riders are video recorded".

Nate, who was sitting on the driver's seat, started the car, and hand drove the car to take an U-turn. After the U-turn, the Uber car was then in the self-driving mode.

The wheel in front of Nate turned by itself to adjust directions. However, Nate kept looking forward, and his hands kept a holding gesture but not touching the wheel at all.

During the trip, Ruben, sitting on the passenger side of the front seats, kept his eye on a laptop in front of him, which was showing a 3D image signal transmitted from the radar on the top of the car.

When a bus was driving in front of the car, Nate took over the car's control. Nate hit the brake, and made an abrupt change of the car's direction manually. The computer in the car beeped once.

"I just took over the car because I want to pass the bus more comfortable. If we let the computer control the car, the car will just stop, follow the bus, or slowly pass the bus." Ruben input something and took a note of this small incident on his laptop.

At the last intersection before the destination, Nate took over the driving again. "The map showing the car will take a longer way to go there, but I know you just need to go to the front entrance of the theater, and I will drive you there directly," he said to the passenger.

About five minutes later, the passenger was sent to the destination safe and sound.

Last December, Uber's self-driving car program in San Francisco met challenge from California regulators. The California Department of Motor Vehicles revoked Uber's autonomous vehicle registration.

Then the California-based company said that it would not apply for the permit and decided to have its self-driving cars delivered via a self-driving truck to Phoenix, Arizona for future pilot tests.

The less regulation environment in Arizona has attracted many companies to do their self-driving tests in the Grand Canyon state.

Before Uber, Google has been testing its self-driving Lexus SUVs in Chandler for four months. And Ford also has been doing road test for its self-driving Fusion for nearly two years.

Arizona Governor Doug Ducey promised less oversight. He even took part in a ride when Uber debut its self-driving car service in Tempe.

However, a self-driving car experience in Tempe has limitations.

As it is now only a pilot experiment, all the Uber self-driving cars run on a set route, which is a rectangular route about 6 miles long around the Arizona State University campus.

During recent weeks, Uber has also faced other challenges, such as one from Google's Waymo, which has sued Uber for stealing trade secrets and patent infringement.

Uber also reverses itself. According to the San Jose Mercury News, the ride-hailing company applied for a permit on Thursday to test its self-driving cars on California roads. Endit