From his vantage point in a car a few dozen feet in front of a 20,000-pound big rig barreling along a Florida highway without anyone behind its wheel, Stefan Seltz-Axmacher felt like everything was going according to plan.
As the founder of self-driving-truck startup Starsky Robotics, he had spent more than two years building to this moment, when a truck with no human sitting in the front seat, no safety driver waiting in the sleeper berth, no human anywhere on board, would trundle along a public road. Now, watching the first two miles of the groundbreaking journey from a lead car riding in front of the tractor-trailer, he confessed that it all felt routine. Maybe even, like the reality of so much of current autonomous-vehicle testing, boring.
And that?s precisely when the truck inexplicably slowed and stopped in the middle of the road. ?I?m thinking, ?This is not planned,? ? Seltz-Axmacher said. ?And so we get out and turn off the engine and start investigating.?
Starsky Robotics engineers tested and developed the autonomous-driving system, which has been installed in the Freightliner Cascadia for more than a year, and had spent a full week conducting dry runs on the stretch of County Road 833 in southern Florida, just north of the Everglades. They had plotted every conceivable contingency and every imaginable edge-case scenario.

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all those things we tested and expected, we never tested shutting down the power to t...