In August, we spent a day driving around with Mr. Cook and his Tesla to assess the progress of this experimental technology. Tesla is driving But watch as the Tesla struggles to make sense of its environment, veering from the road into a motel parking lot. The experiences of beta testers like Mr. Cook are a window into the enormously ambitious and expensive bet that Tesla is making on self-driving technology. Guided by Tesla’s self-driving technology, the car drove along the river and over a bridge before reaching an intersection lined with trees. These companies are now preparing self-driving car services that will operate without backup drivers in places like San Francisco and Austin, Texas.

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