2021 E-Class will use capacitive sensing to check for hands on the wheel

Mercedes-Benz has just unveiled the 2021 E-Class, and like many of its German luxury siblings, it will come equipped with the company’s latest driver-assistance features. But the new E-Class also changes how the car registers whether the driver is paying attention while using those features, as Mercedes-Benz is introducing a new wheel with capacitive sensing.

Previously, the E-Class (and other Mercedes-Benz vehicles) determined whether a driver’s hands were on the steering wheel by measuring movement in the wheel. The problem with this method is that it’s often hard to get the balance right of how much movement needs to be measured to say for sure that a hand is on the wheel. Set the bar too low, and it’s easy to cheat. Too high, and you’re asking the driver for input that could change the physical trajectory of the car.

Now, though, the new E-Class will just know that the driver’s hands are on the wheel. That doesn’t mean there won’t be ways to cheat the system — there always are. But capacitive sensing could be a more straightforward approach than measuring steering input.

This all matters because new cars are becoming increasingly filled with tech that can take over some of the tasks of driving. The new E-Class, for example, has active steering assist (which helps keep the car in the center of the lane), adaptive cruise control (which can adjust speed automatically based on what the cars in front are doing), active brake assist (which can stop the car from city speeds for stationary vehicles and crossing pedestrians), and more.

The problem is that, as cars become better at handling these tasks, there’s a greater risk that humans will become overconfident in those abilities.

This was one of the central themes during a three-hour-long National Transportation Safety Board hearing last week in Washington, DC about a fatal 2018 crash involving Tesla’s Autopilot.

In that crash, the driver’s Model X drifted left out of an HOV lane and into a concrete barrier, despite the fact that he was using Tesla’s driver assistance system, Autopilot, at the time.

There were a number of factors that contributed to that driver’s death, like that the safety device in front of the concrete barrier was damaged, and that the highway’s lane lines were faded. But the NTSB determined that the driver’s overconfidence in Autopilot’s abilities was one of the main probable causes. In fact, the safety board’s investigative team found that he was playing a mobile game on his smartphone right before he crashed into the barrier.

Tesla uses a torque sensor to measure whether a driver’s hands are on the wheel when Autopilot is active. And if it doesn’t measure enough torque every 15 seconds or so, it will begin a series of escalating warnings to the driver before ultimately deactivating Autopilot until the car is restarted. But even those protections weren’t enough to stop that driver from misusing Autopilot in that 2018 crash.

Other companies have gone in a much different direction when it comes to monitoring drivers’ attention while Autopilot-like features are active. Super Cruise, which is the driver assistance package on Cadillac’s cars, uses eye tracking cameras to make sure the driver is looking out at the road ahead. Cadillac is so confident in this method’s effectiveness that it allows drivers to use Super Cruise hands-free, though only on highways that the company has specifically mapped out. (Cadillac also uses capacitive sensors in its steering wheel in combination with the camera system.)

Exactly which kind of driver monitoring system is best is still hard to say; all of these technologies are still relatively new. But more of them are coming to market every year. The Audi E-Tron has a capacitive steering wheel, for example. And Ford’s new Mustang Mach-E will feature a Super Cruise-like camera system when it hits the road at the end of this year. Tesla CEO Elon Musk, meanwhile, is sticking with torque sensors, having said in 2018 that camera systems are “ineffective.”

The NTSB acknowledged this scattered approach last week, and as part of the conclusion of its investigation, recommended that the National Highway Traffic Safety Administration help draw up driver monitoring system standards that would “minimize driver disengagement, prevent automation complacency, and account for foreseeable misuse of the automation,” and require it in all vehicles with Autopilot-like features.

Meanwhile, if Mercedes-Benz’s capacitive approach seems to work well, it could spread to other vehicles in the company’s lineup, as it says the tech is part of a whole new steering wheel generation.

But regardless of the method, NTSB chair Robert Sumwalt’s words from last week’s hearing are wise to keep in mind: “if you own a car with partial automation, you do not own a self-driving car. Don’t pretend that you do.”

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