All it takes is one edge case to get federal regulators to pay attention. GM's Cruise subsidiary has performed over 120,000 unprotected left turns in its self-driving development vehicles, but a single extreme scenario that resulted in a collision ended up prompting a recall.
Cruise issued a recall for a specific software release (Delta/2022.05.13.00) in 80 examples of the automated driving system installed on its Cruise AV self-driving development vehicles. The recall points to a specific scenario that involves an unprotected left turn, which is a left turn where oncoming traffic has the right of way. Think of a left turn without an accompanying stop sign or a green turn arrow, and you've got the idea.
Here's how the collision occurred. A Cruise AV was making an unprotected left and its software noticed a human-operated vehicle approaching at 40 mph in a 25-mph right-turn lane. The software determined that a crash was likely if the AV continued turning left as the oncoming car approached the intersection, so it stopped midturn. However, the human speeder then decided to move out of the turn lane and continue straight, speeding through the intersection, where it collided with the stopped AV's passenger-side rear quarter panel. Two people were injured.
Here's how the National Highway Traffic Safety Administration's safety recall report (PDF) phrases the safety risk: "In the rare circumstances described above, a Cruise AV with [the autonomous driving system in question] may, when making an unprotected left, not have correctly predicted nor has been sufficiently reactive to the sudden path change of a road user violating demarcated lane usage and operating at excessive speed, which could increase the risk of a crash."
Basically, the software was stuck between a rock and a hard place, and it made a call that seemed right, until the oncoming human driver did something well outside the realm of expected behavior.
Cruise already updated its software in July, but it still filed a report with NHTSA. "We submitted this voluntary filing in the interest of transparency to the public; it pertains to a prior version of software and does not impact or change our current on-road operations," a Cruise spokesperson wrote in a statement emailed to CNET. "Rather, the report explains how the Cruise AV responded to an oncoming vehicle speeding in the wrong lane, and how through our normal course of continuous improvements, Cruise AVs are even better equipped to prevent this singular, exceptional event."
According to Reuters, Cruise slowly reintroduced unprotected left turns after temporarily disabling them following the collision.