Who should self-driving cars (SDC) be programmed to save when it isn’t possible to save everyone?
That is the key question posed by a discussion paper exploring the thorny issue of ethics and autonomous vehicles. The report — authored by Michael Haines, CEO of Vanzi — advocates for a set of uniform rules based on human values that can be put into law and followed by all SDCs as any accident unfolds.
The proposed rules are an effort to avoid machines making decisions on a case-by-case basis, which Haines argues would create uncertainties for public safety and litigators.
The report proposes an ethical hierarchy that the SDC should be programmed to follow when the car — rather than the human — is in actual and legal control of the vehicle. On balance, the ethical response is to take a path that saves people in the following order priority:
- All unprotected bystanders;
- The occupants of other vehicles;
- The occupants of the SDC;
- The party at fault (that causes the SDC to take evasive action).
It is up to each manufacturer to ensure its SDC system obeys the law and drives defensively. This includes taking appropriate evasive action when others are at fault.
Deciding who to save where there are no ‘safe paths’
Haines writes, “Take the case of an oncoming motorbike rider who has fallen while overtaking and is skidding towards the SDC at high speed. Assume, even with hard braking, the SDC will likely run over and kill the rider, with likely only minor injury to the occupants. On the other hand, veering around the skidding rider to save them would send the SDC into the path of an oncoming truck at high speed, likely killing the occupants, destroying the car and causing major damage to the truck.
“There does not seem to be any rational argument why society should mandate ‘self-sacrifice’ by the occupants of the SDC in these, or similar, circumstances. Ethically, we may rule that where there is a choice, the SDC should try to save the occupants from major injury or death ahead of the ‘party at fault’.”
The argument for self-preservation
The report examines the argument that the SDC should put the safety of its occupants ahead of all others, based on the principle of “self-preservation” enshrined in British tort law.
In the case of Scott v Shepherd a person threw a lit torch into a crowd. Another person picked it up and threw it away to protect themselves, causing harm to a third party. It was held that the person who originally threw the torch was the cause of all the harm that ensued, and hence liable for damages.
The report states, “The original thrower is analogous to the ‘at-fault party’ who causes an SDC to have to take evasive action to avoid injury to the occupants. Based on Scott v Shepherd, it could be argued that the SDC is entitled to save its occupants by swerving into a pedestrian or bike rider, etc. to, say, avoid a high-speed head-on collision with a truck that has veered into its path.”
However, the author makes clear that, ethically, the principle of “self-preservation” is not absolute. There is also a general duty of care towards others. Society may prefer the premise that if the choice is between likely major injury or death for either the occupants or other innocent bystanders, the SDC should limit the flow of harm and always save the bystanders.
“Ethically, it is hard to argue that the SDC should kill the wayward pedestrian or fallen rider, even though they are ‘in the wrong’, to save the occupants from (at most) likely minor harm.”
The report proposed a potential countermeasure to protect innocent bystanders: the concept of an impermeable “virtual guard rail” between the SDC and pedestrians. The benefit of such a virtual barrier is that it can be removed instantly if it is clear that there are no people — creating an escape route for the SDC.
“In this case, any car faced with an oncoming truck could not evade collision by running onto the footpath or bike path due to the hypothetical guard rail. The result being that an ‘unprotected bystander’ is saved and the ‘occupants of the SDC’ are killed. Their unfortunate death would not be due to the fault of the SDC, but to the truck driver (or other cause for the truck being on the wrong side of the road),” Haines writes.
Accepting the principle of the “virtual guard rail” establishes the ethical rule that an SDC should prioritise the safety of unprotected bystanders, ahead of both the occupants and the party at fault.
In this scenario, “It would simply mean the occupants’ time was up, due to factors beyond their control, or the control of the SDC. In this case, the people who caused the accident would be held liable for all damage and harm, like the initial thrower of the lit torch.”
Causing death versus minor injury
“Ethically, it is hard to argue that the SDC should kill the wayward pedestrian or fallen rider (even though they are ‘in the wrong’), to save the occupants from (at most) likely minor harm,” the report states.
Therefore, it is argued, this rule should state that the SDC should avoid “likely” major injury or death to the party at fault, even at the expense of “likely” minor injury to the occupants — based on published impact thresholds below which no or minor injury is the expected outcome. In the case of hitting poles, trees, embankments and other solid objects, the consequences of the impact can be directly assessed by the SDC manufacturer as part of the car’s safety rating. If the occupants sustain major injury or death (instead of the expected minor injury), there may be a claim against the SDC manufacturer if it is due to a malfunction in the safety system.
The thresholds for collision with other vehicles would need to be established by the industry as a whole.
As a final note, the report states that any completely autonomous unoccupied SDC should be required to crash in order to avoid hurting anyone. The owner of the SDC would then have a claim against the at-fault party, whose identity is hopefully captured via its sensor recordings if they fail to stop.
The full report is available at Which-50.