In a 2014 patent, Google takes this concept further, describing how an automated vehicle might position itself in a lane to minimize its risk exposure. The company cites the example of an automated car driving on a three-lane road with a large truck on its right and a small car on its left. To optimize its own safety, the automated car would position itself slightly off-center in the lane, closer to the small car and away from the large truck.

This seems sensible, and it’s probably something that most people do, either consciously or unconsciously. Still, it raises ethical concerns. By moving toward the smaller vehicle, the automated car has decreased the overall risk but is now unfairly distributing it. Should the small car have to take on more risk simply because it’s small? If this problem involved a single driver’s habits, it wouldn’t matter much. But if such risk redistribution were formalized and applied to all driverless cars, it could have substantial consequences.

In each of these examples, a car is making a decision about several values—the value of the object it might hit as well as the value of its occupant. Unlike people, who make these decisions instinctively, an automated vehicle would do so as the result of a carefully planned strategy of risk management, which defines a risk as the magnitude of misfortune associated with the feared event multiplied by its likelihood.

Google also patented an application of this type of risk management in 2014. In this patent, the company describes a vehicle that may want to change lanes to get a better view of a traffic light. Or the vehicle could choose to remain in its current lane, where it would avoid taking on the small risk of crashing—say, because of a reading from a faulty sensor—at the cost of that traffic-light information. Each potential outcome is assigned a likelihood as well as a positive or negative magnitude (either a benefit or a cost). Each event’s magnitude is multiplied by its likelihood, and the resulting values can be summed. If the benefits outweigh the costs by a reasonable margin, the vehicle will execute the action being considered.

The trouble is that the risk of crashing is incredibly small—the typical driver in the United States crashes once every 257,000 kilometers (160,000 miles) or about every 12 years. Therefore, even with the avalanche of driving data that will come once automated driving takes off, it will be some time before we have plausible crash probabilities for each of the many possible scenarios.

And assigning the magnitude of damage is even harder. Property damage costs are simple enough to estimate—the insurance industry has a lot of experience with it—but injuries and deaths are another story. There’s a long history of assigning value to a life, and it is normally expressed as the amount of money one could justify spending to prevent a statistical fatality. A safety improvement that has a 1 percent chance of saving a life for 100 people represents one statistical fatality. The United States Department of Transportation recommends spending US $9.1 million to prevent a fatality, a number inferred from market data, including the premiums that people demand for taking hazardous jobs and what people are willing to pay to buy safety equipment, such as smoke alarms. Not only safety must be weighed in the balance but also the cost of lost mobility or time, which the USDOT puts at $26.44 per hour for personal travel.

It all seems very tidy. But viewing risk in terms of lost lives and wasted commuting time fails to capture much of the moral considerations surrounding how we expose people to risk. For example, an automated vehicle that treated every human life alike would have to give more room on the road to a motorcyclist riding without a helmet than to another one wearing full protective gear because the unprotected one would be less likely to survive a crash. This seems unfair—why should the safety-conscious rider be punished for his virtues?

Another difference between robot ethics and the human kind is that theirs can be warped, even by programmers who had only the best of intentions. Imagine that the algorithm operating a driverless car adjusted the buffering space it assigns to pedestrians in different districts, which it might identify by analyzing settlements from civil proceedings involving crashes. Although this is a perfectly reasonable, well-intentioned, and efficient way of controlling a vehicle’s behavior, it can also lead to bad outcomes if, for example, the actual reasons injured pedestrians settled for less were because they lived in low-income neighborhoods. The algorithm would then inadvertently penalize the poor by providing them smaller buffers and slightly increasing their risk of being hit when out for a walk.

It is tempting to dismiss such concerns as idle academic maunderings, but there is no way around them, because computer programs take things quite literally. The time to figure out the consequences of an action is before they happen—in design, rather than the patching phase.

And this is partly why so many researchers use hypothetical situations in which the vehicle must decide between two or more bad outcomes. The most famous of these is the “trolley problem,” [pdf] in which a trolley is threatening to collide with unsuspecting children and the only way to stop it is to throw a fat man over the side of a bridge and onto the track’s switch. (The man’s weight matters: Otherwise, a self-sacrificing onlooker could jump off the bridge himself.) Do you sacrifice one life to save many by such a positive action? If your answer is “no,” consider this: You’d no doubt be willing to sacrifice one life to save many by refusing to act—so how can you justify the apparent contradiction?

There is a substantial literature on such thought experiments, and indeed, they allow you to stress-test simple and straightforward ethics systems and to find areas where a bit more nuance would be helpful. Suppose an automated vehicle were programmed to avoid pedestrians at all costs. If a pedestrian were to suddenly appear in a two-lane tunnel, and the vehicle couldn’t stop in time, the vehicle would be forced to swerve, even into the path of an oncoming bus loaded with passengers. The plausibility of that specific scenario is less important than the flaw it exposes in the vehicle’s logic—that valuing pedestrian safety as categorically more important than that of any other road users can actually be much more dangerous in certain situations.

The ethics of road-vehicle automation is a solvable problem. We know this because other fields have handled comparable risks and benefits in a safe and reasonable way. Donated organs are distributed to the sick based on metrics based on quality-adjusted life years and disability-adjusted life years, among other variables. And the military draft has added exemptions for certain useful professions, such as farmer and teacher.

Automated vehicles face a greater challenge. They must decide quickly, with incomplete information, in situations that programmers often will not have considered, using ethics that must be encoded all too literally in software. Fortunately, the public doesn’t expect superhuman wisdom but rather a rational justification for a vehicle’s actions that considers the ethical implications. A solution doesn’t need to be perfect, but it should be thoughtful and defensible.

About the Author

Noah J. Goodall is a research scientist at the Virginia Transportation Research Council, in Charlottesville, Va.


Read more: Can We Trust Robots?

Read more: Would You Trust a Robot Surgeon?

Read more: Do We Want Robot Warriors to Decide Who Lives or Dies?