It happened while I was reviewing a European automaker’s flagship luxury sedan.

I was creeping along on Interstate 93 in Boston, testing the active cruise-control system and marveling at the car’s ability to bring itself to a stop every time traffic halted. Suddenly an overly aggressive driver tried muscling into traffic ahead of me.

Instead of stopping, however, my big-ticket sedan moved forward as if that jerk wasn’t even there. I slammed on the brakes — stopping just in time — and immediately shut off the active cruise control.

It was a stark reminder that even the best technology has limits and a good example of why drivers should always pay attention behind the wheel. But it got me thinking:

What would’ve have happened if I hadn’t stopped?

It’s an intriguing, and increasingly relevant, question as automakers pack their cars with ever more electronic nannies and the government ponders requiring things like back-up cameras. Semiautonomous systems are becoming more common as our cars do everything from keep us in our lanes to prevent us from hitting pedestrians. If any of these systems should fail, how would an insurance company deal with it?

We ran these questions past automakers, the insurance industry and attorneys. Although semiautonomous vehicle technology is evolving quickly and the day of the driverless car is within view, there’s broad agreement that drivers almost always are responsible for what happens with their cars. In those cases where the technology truly is to blame, the problem can be handled within the current legal framework.

Eyes and Ears Beat Radars And Sensors

Even as Google and DARPA bring us truly entirely autonomous vehicles, people must remember that nothing in showrooms offers any technology designed to function without a driver’s input and attention. Cars like the Volvo S60 and Mercedes-Benz E550, to name but two examples, have semiautonomous features designed solely to assist the driver.

“Whether it’s lane assist or blind spot assist, they have the word ‘assist’ in there because we want to communicate that this is a tool to help the driver drive safely,” said Wade Newton. He’s the spokesman for the Alliance of Automobile Manufacturers, a public policy advocacy group for the auto industry. “I’m not aware of any automaker that markets those kind of devices as anything other than driver assist.”

In fact, many of these safety systems are meant to function without you even knowing they’re there. Their only purpose is to slam on the brakes or steer the car back into your lane if a collision is imminent. In other words, if you notice the systems at work, you’re doing it wrong. Put down the phone and drive.

That’s a key consideration. No automaker wants to see drivers fiddling with radios and cell phones, lulled into a false sense of security and complacency thinking the car will bail them out of trouble. That’s why manufacturers, not to mention the owner’s manuals and dealers, bluntly warn drivers of the limits of active safety.

“Whenever possible we tell and remind our customers that assistance systems are no substitute for active driving,” said Dr. Joerg Breuer, senior manager for active safety at Mercedes-Benz. “And incidentally drivers realize quickly that adaptive cruise control cannot be used as an auto-pilot, so there is no incentive here to engage in distracting activities.”

Of course, people forget what the dealer muttered as he handed over the keys. They lose the owner’s manual. And they probably don’t offer anything in the way of a tutorial when they sell the car to the next guy 10 years later. For that reason, active-safety systems are designed to be intuitive and unintrusive so even the biggest Luddite can figure them out easily.

“Drivers learn very quickly,” said Breuer, noting that most people pick up the nuances of a new technology within minutes or hours.

My Car Did It

Even the best drivers often are confronted with difficult situations where active-safety technology comes into play: Driving a vehicle with blind spots makes merging and parking tricky, or following a car with faulty brake lights, for example. In such cases, the failure of a semiautonomous active-safety system might cause an accident. But we’ve already got systems in place to handle any liability issues new technology might bring.

“The litigation system can really handle this in a fairly routine way,” said David Snyder, vice president and associate general counsel at the American Insurance Association, an insurance industry group. “It’s all about factual causation. In other words, the driver is presumed to be in control of his or her vehicle, but if the driver feels that there have been some facts supporting the notion that the equipment caused in whole or in part the accident, that driver would probably bring in the manufacturer of the equipment.”

It’s a common practice, especially in serious accidents where a vehicle may not have functioned properly. It’s why Toyota got involved in the unintended acceleration debacle, and how the Ford Pinto earned its 15 minutes of infamy.

Imagine that we hadn’t hit the brakes in time and we’d plowed into that jerk on I-93. Not only would we probably not be invited to test any more cars from that manufacturer, but we’d also endure an investigation to determine liability. We posed the — thankfully — hypothetical scenario to Tom Baker, a liability and insurance law professor at the University of Pennsylvania Law School. He said liability would depend upon the facts of the case.

“First, the driver of the car might have used the cruise control system improperly,” he said. “If so, he or she would be liable and his or her automobile liability insurance company would have to pay.”

Bad news for us, and lucky that we were paying attention.

“Second,” Baker said, “the cruise control system might not have functioned in the way that it was designed to function due to some programming or other mistake by the manufacturer. Third, the cruise control system might not have been designed in a reasonably safe way.”

In both of these cases, the cruise control system’s manufacturer and distributor would be liable, and their insurance company would pay the claim.

Of the three possibilities, Baker said liability would be easiest to prove if a system failed to work properly.

“It would be analogous to a ‘manufacturing defect,’ which is a slam dunk case for plaintiffs in the product liability context,” he said.

It would be harder to demonstrate that an accident was caused by a possible design defect, or to show the manufacturer did not provide clear instructions for the use of an active-safety system.

Failure Is Not An Option

That said, failure of semiautonomous vehicle systems is exceedingly rare. No one we talked to for this story could point to a real-world scenario where an active-safety technology failed and caused an accident. Why? Because such systems are intensively and thoroughly tested before they’re brought to market. They also feature comprehensive self-diagnostic tests that run every time they’re engaged.

“To verify that our innovations do work in the real word, i.e. with ordinary drivers in all kind of traffic situations, we conduct intensive testing to collect both objective and subjective data,” Breuer said.

Mercedes-Benz collected more than 100 terabytes of data racked up during more than 1 million miles of real-world testing before customers could purchase cars with features like Distronic Plus and Brake Assist. The radar-based system helps drivers maintain a safe following distance and will slow the car, or even stop it, in an emergency.

Most of the advanced tech systems run intense self-diagnostic procedures whenever the driver turns the key, then continues running as the cars are driven.

“All our systems constantly run diagnostics routines,” Breuer said. “If a problem is detected the system will automatically be deactivated and a message to the driver will be triggered.”

For example, if mud or snow covers over a sensor, a message appears on the dashboard clearly telling the driver that an active-safety system is unavailable.

No Substitute For Good Driving

Semi-autonomous vehicles and active-safety systems can serve as a second set of eyes and ears, prevent collisions and even warn drowsy drivers if they nod off. Volvo’s pedestrian protection system, for example, uses cameras and radar to help avoid collisions with anyone who steps in front of the car.

But all this tech is no substitute for the driver actually driving. That’s why regulations require designing active-safety systems with drivers in mind.

For instance, active cruise-control systems must disengage once the vehicle comes to a stop, forcing the driver to pay attention and not rely on the car to automatically accelerate once traffic starts again. Technology could allow automakers to build cars that do almost anything we might want, but such technology probably won’t be adopted if it lets drivers to do anything but pay attention to the primary job at hand — driving safely and responsibly.

“That’s always the balancing act, and that’s why we do such research when it comes to driver distraction,” said Newton. “There are a lot of technologies that might not make the cut because they’re not helpful to the driver.”

Photo: A bus accident on Empire Way, 1933. (Seattle Municipal Archives/Flickr)