"trialing" is a dreadful misnomer. They are "testing", rather.

Problems with driverless cars or computer decision makin which is linear, not Complex system, the vehicles are driving in. Innumerable problems can come up, unpredictable and only humans can solve those. Low traffic out in the boonies such as east/west across NV, are easy to do.

Until ya get to Sparks/reno. Then it all slows way down.

The problem is this, using vast amounts of data from cars and truck operating is simply too complex to solve/sort.

This is how it can be done, directly, testably, and clearly. No fuss, no muss, Expert systems based.

https://jochesh00.wordpress.com/2017/06/10/problem-solving-for-self-driving-cars-a-model/