Saturday, October 21, 2023

Safety Analysis of Two Cruise Robotaxi Pedestrian Injuries

Cruise has now had two pedestrian injuries in San Francisco, with the more severe one being complicated because it involved a pedestrian first hit by another vehicle.  NHTSA has launched an investigation based on those injuries and at least two other public video reports of close encounters. This makes available the relevant crash reports, so we have more direct information about what happened. The question asked in this piece is what can be done to avoid similar crashes in the future.


On a numbers basis, two pedestrian injuries in a span of fewer than six weeks for a fleet of a couple hundred vehicles in San Francisco is a concern, so this is worth some analysis based on available information.

  • First injury: Aug. 26, 2023.  A pedestrian stepped off the curb into a crosswalk right in front of a Cruise vehicle at the change of a traffic light. The Cruise swerved, then braked. Impact at 1.4 mph. Pedestrian transported by EMS.
  • Second injury: Oct 2, 2023. A pedestrian crosses on the opposite side of a cross-street in front of the Cruise vehicle and another vehicle next to it. Both vehicles proceeded through the intersection as a pedestrian was in a crosswalk across their paths. The other vehicle struck the pedestrian at an undisclosed speed, who was then run over by the Cruise vehicle and trapped under it with severe injuries.
In both cases the injuries were severe enough to require transport. For the second crash the pedestrian was almost completely underneath the rear of the vehicle.  (It is worth noting these descriptions are written 100% by Cruise. The reader should assume the most favorable-to-Cruise possible interpretation of events has been presented. If something obviously relevant is omitted, such as the impact speed for the second injury, one is justified in assuming it would be unfavorable to Cruise if disclosed.)

Cruise, predictably, blames others for both crashes, although in both cases without review of the video it is difficult to be sure that is really true. However, we set blame aside and instead ask the question: what can be done to avoid the next pedestrian injury in similar circumstances.

First Pedestrian Crash


For the first crash, the question is whether a reasonable human driver would have had contextual clues that this pedestrian was about to enter the crosswalk even though the light had changed. For example, were they running to catch a bus pulling up to a stop across the street?  Were they "distracted walking?" Or were they at a complete stop on the curb and literally jumped out into the street? Opportunities for improvement include asking these questions:
  • Were there obvious contextual clues that the pedestrian would attempt a last second crossing? What are common cases, and are they covered by the Cruise AV design?
  • Why did the vehicle swerve before stopping instead of doing both at once?
  • Could/should the Cruise vehicle have followed a less aggressive acceleration profile given the likely risk of a pedestrian entry into the crosswalk in that type of circumstance?

Second Pedestrian Crash


For the second crash, things are more complicated. Let's break down the sequence, taking into account the initial setup sketched below (note that both vehicles are in the middle of an intersection, but the sketch tool I used did not make this easy to represent):

  1. There are two vehicles starting through an intersection, side by side, with two lanes in that direction of travel. From a top view the other, human driven, dark-colored vehicle is on the left (faster lane) and the lighter-colored Cruise is on the right (curb lane).
  2. A pedestrian is walking across the far side of the intersection in the crosswalk. At the same time, both vehicles accelerate into the intersection. The most likely situation is the Cruise vehicle was a bit behind the other vehicle (although this is an educated guess based on the description of the events).
  3. Cruise says the pedestrian entered the crosswalk after the light changed, crossed in front of the Cruise vehicle, then stopped in the other vehicle's lane. The other driver presumably thought the pedestrian would clear the travel lane in time, and did not slow down.
  4. The other vehicle hit the pedestrian. Cruise says the pedestrian was deflected back into the Cruise vehicle's lane.
  5. The Cruise vehicle "braked aggressively" in response to a surprise pedestrian appearing in its lane, but hit the pedestrian shortly after.
  6. The Cruise vehicle had sufficient forward speed that it ran over the pedestrian and came to a stop with the pedestrian trapped under the rear axle. Both of the pedestrian's feet protruded from under the vehicle by the left rear tire, with that tire on top of one leg. (Photo link below.)
  7. The pedestrian was severely injured by a combination of the two vehicle strikes. Information about the ultimate outcome for that pedestrian is not currently available, although we hope that a recover is quick and as complete as possible.

California Rules of the Road have an interesting requirement for crosswalks:

"(c) The driver of a vehicle approaching a pedestrian within any marked or unmarked crosswalk shall exercise all due care and shall reduce the speed of the vehicle or take any other action relating to the operation of the vehicle as necessary to safeguard the safety of the pedestrian."  (emphasis added)

It is interesting to ask if the Cruise vehicle actually exhibited "all due care."  It likely did not reduce speed from its normal green light acceleration, or Cruise would have taken credit for having done so.  (If they want to provide more details I will gladly update this statement.)

Of note is the Cruise position that their vehicle stopped as quickly as possible once the pedestrian was in their lane, in effect claiming the collision was unavoidable. But that position is not necessarily true in the larger context, especially if one learns from this crash for the next potential pedestrian crosswalk collision. The question is when the Cruise AV could have stopped. There are at least three possible decision points for stopping to avoid this collision with the pedestrian, and the Cruise vehicle appears not to have exercised the first two:

  • The light changes green, but there is a pedestrian still in the crosswalk in the Cruise vehicle's direction of travel in front of the Cruise vehicle. Did it slow down?  Or execute a normal acceleration because it predicted the pedestrian would be clear by the time it got there?   A prudent human driver would have waited, or more likely crept forward while waiting to signal cars behind it not to honk for failing to recognize a green light.
  • The pedestrian clears the Cruise lane, but the Cruise vehicle clearly sees the pedestrian about to be hit by the adjacent vehicle. The Cruise vehicle could have (I would argue should have) stopped to avoid being close to an injury event. Expecting it to predict a pedestrian collision trajectory is asking a lot -- but it should have stopped precisely because it cannot predict what will happen after such a collision. Safety demands not going fast past a pedestrian who is about to be hit by another vehicle in an adjacent lane. But this is precisely what the Cruise vehicle did.
  • The pedestrian lands in the Cruise lane and the Cruise vehicle has not slowed down yet. By then it is too late, and it runs over the pedestrian.  This could likely have been avoided by a prudent driving strategy that addresses the previous two decision points.

The Redacted Confidential Business Information

(This section added October 25, 2023 based on new information.)

California DMV issued an order suspending the driverless operating permits for Cruise robotaxis on October 24, 2023 as a response to the circumstances of this second crash.  Link to order here.

This order brought to light that after the vehicle had stopped post-crash, it started movement again with the pedestrian still under the vehicle, dragging that victim about 20 feet at a speed up to 7 mph, which was said to contribute to severe injuries. This strongly suggests the vehicle did not account for a pedestrian being trapped underneath it when deciding to move. (It is possible a remote operator was unaware of the trapped pedestrian and remotely commanded a pull-to-side maneuver. We'll have to see what is revealed during any investigation.)

Cruise also published a blog post with additional information that day. A straightforward update to the crash report is to add at the end as at least part of the "redacted confidential business information" the following (quoted from the Cruise blog post): 
"The AV detected a collision, bringing the vehicle to a stop; then attempted to pull over to avoid causing further road safety issues, pulling the individual forward approximately 20 feet."

This certainly makes Cruise look bad, but that is not an acceptable reason for a redcation. It is difficult to understand how this can reasonably be characterized as "confidential business information" in a mandatory crash report.

Calling Emergency Services

Also crucial for practical safety, but barely talked about, is notification of emergency services ("call 911"). News reports indicate that a passer-by called 911, not Cruise. In fact, in neither collision report do they take credit for notifying emergency services. This is a glaring omission that needs to be addressed.

Consider: they had a vehicle tire on top of a pedestrian's leg and did not call 911. (Again, if this is incorrect I will update this statement when I get that information.) That's a HUGE problem nobody is talking about. A human driver would have realized they just ran someone over and either called 911 or asked someone to do so. If there had been no passer-by, how many minutes would that pedestrian have been trapped under the car before help was summoned?

The Cruise AV and its support team need to realize an injury has happened and take immediate action. It would be no surprise if the remote operators had no idea what the vehicle had run over. By the time they download and review video logs (or whatever) that pedestrian has been trapped under the vehicle for a while. That's not acceptable. They need to be able to do better.

Cruise Safety Record

The first pedestrian injury happened just over two weeks after the August 10th California PUC meeting that granted operating permits to Cruise. That report was overshadowed by the crash apparently due to failure to yield to a fire truck on August 17th. That night also saw another injury involving a collision to a different vehicle driver.  So we are seeing a steady stream of injuries.

Cruise blames crashes on other parties to the maximum degree possible, and ignores injuries where it is less than 50% at fault (there have been others; notably a very ill-advised left turn maneuver by a Cruise robotaxi that resulted in multiple injuries).  Safety is not achieved by blaming others. If Cruise vehicles are crashing and injuring people more often than other vehicles, then that is an increased rate of injury regardless of blame.

A company with a responsible safety culture would be asking what they can do to reduce the risk of future injuries -- regardless of blame. We will have to wait to see the outcome of this NHTSA investigation, and whether Cruise proactively improves safety or waits for NHTSA to force the issue.

As a note to likely responses to this analysis: comparisons to human driver errors are not productive. Indeed, another driver hit the pedestrian first in the second crash. But another driver being negligent does not forgive imprudent driving behavior from a robotaxi that is being relentlessly touted as safer than human drivers. They should be continuously improving, and our hope is that this analysis highlights areas that they and other robotaxi companies need to improve.

Supporting Information


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