The War For Autonomous Driving, Part Deux: The 2017 Mercedes-Benz E-Class

A hardware champion enters the software age.

byAlex Roy|
Self-Driving Tech photo

What follows is a full review, as promised, of the 2017 Mercedes-Benz E-Class's Advanced Driver Assistance Systems (ADAS), including the new Drive Pilot feature and what Mercedes calls "semi-automated" driving features. This is a follow-up to my original and disputed comparison of this technology suite to Tesla's Autopilot semi-autonomous driving capabilities.

I note that this test included, over the course of one week, about 250 miles of real-world testing in a top-of-the-line E-Class with Premium 3 Package; 400 pages read (and re-read) of the E-Class owner's manual; heavy perusal of the company's website and public statements regarding Drive Pilot; and two undercover visits to dealerships to ask questions of the sales people.

I mention all of this because my assessment on any driving-assist technology—and the E-Class has, depending on your categorization, anywhere between 15 and 20 examples—exists within the related contexts of understanding and trust. That is to say: 1.) even a well-executed technology is considered a failure if I don't understand how to use it after reasonable effort; and 2.) I personally won't use any automotive safety technology I don't trust to work, as advertised, almost 100 percent of the time.

Here’s what I learned in a week of driving around New York City with an open mind and my hands on the wheel, using everything exactly as Mercedes said it was designed to be used.



Forward and rear “multi-mode” wide-angle radars provide 360 degrees of coverage, and will “prime the seats and brakes” before a collision. From what I can ascertain from the manual (because my real-world test didn't extend to actually crashing the car) the seat bolsters and brake pads will both anticipate a crash, with the former firming up to better stabilize the passenger and the latter moving closer to the rotors to decrease braking time. The rear radar is the single biggest safety advantage the E-Class has over the Tesla Model S. This should be mandatory in all cars, and it can’t be turned off, which is the right choice.

ESP Dynamic Cornering Assist

This is excellent, mostly because it didn’t activate once, and I drove the car hard enough that it would have in several competing models. I remember when these were so invasive that even people who wanted it would turn it off. In this car, you can leave it on; it won't bother you until you absolutely need it.

Adaptive Braking Technology

Real "driver assistance," in that it improves the braking that's already under my control—exactly what I want—by decreasing brake response time depending on conditions. Convenient, because it also can't be turned off.

Head-Up Display

Nice and bright. If you like these, use it. Is it ADAS? It displays collision warnings and DISTRONIC speed/status, so I suppose. Personally, I found it too small and distracting to be of use, so I turned it off.

Active Emergency Stop Assist

If you remove your hands from the wheel for more than 45-60 seconds, visual and audible alerts will sound. If you don’t place your hands on the wheel, the car will gradually bring itself to a full stop. For anyone confused enough to think that this car (or any car) actually drives itself, this is essential safety technology.


Active Brake Assist

Active Brake Assist w/Cross-Traffic Function

Congestion Emergency Braking

Rear Cross-Traffic Alert

Anything that decreases the chances of striking something is a good thing. Do these work? The short answer: yes, to a point. Sometimes there were alerts. Sometimes not. Sometimes the car braked when it shouldn’t have. The system did see most of the jaywalkers in NYC's congested Chinatown area, but not all of them; it missed one that, thankfully, I didn’t.

When Active Brake Assist engages, it does so late and very aggressively, even on the “Early” setting. It made me so nervous that I wanted to disengage it so I wouldn’t rely on it. That may sound counterintuitive for emergency safety technology, but my main issue was that I couldn't tell if the Cross-Traffic Function—the job of which is to identify cars and pedestrians on a course perpendicular to that of the vehicle—was linked to Active Brake Assist, or not. The website lists "Active Brake Assist" and "Active Brake Assist w/Cross-Traffic Function" as separate systems, which makes no sense. I left it on, but reluctantly.

Active Blind Spot Assist

There are two steps to this tech. If a car is hanging out in your blind spot, a visual warning is displayed on that side's rearview mirror; if you then put on your turn signal indicating movement toward that vehicle, “a course-correcting brake application may be applied.” I like the visual and audible warnings, but hate the idea that the car might brake at the wrong moment and confuse me at the point of decision. Also, why does it apply braking and not some gentle counter-steering? I chose not to find out the hard way and risk a crash. Best to leave this on, and not trust it.

Attention Assist

Intended to alert a fatigued driver that he should stop and rest, this appears to be nothing more than a countdown clock rather than something tied to driving behavior feedback. I had to pee more often than this thing went off.

Car-to-X Communications

Mercedes alleges the new E-Class connects "to a central information resource, to send you in-car updates about driving conditions before you get to them. Your car can also report hazards, to help other E-Class drivers." This is featured prominently on the E-Class website:

See that footnote at the end there? Here's part of the disclaimer:

[1] Delayed availability. See your dealer.

Car-to-X services operate only where cellular and Global Positioning System satellite signals are available, which are provided by third parties and not within the control of Mercedes-Benz USA, LLC...System cannot detect and/or report every road hazard, and its effectiveness depends on the presence of other vehicles equipped with Car-to-X Communication.

Great in theory, but basically, the infrastructure this system is supposed to talk to is largely nonexistent at this point. Self-driving car wunderkind George Hotz thinks this is useless. I'm inclined to agree.

Crosswind Assist

Does exactly what you think it does, by automatically applying the brakes as necessary should a strong crosswind start to take you out of your lane. It wasn’t windy enough to find out how well this works, but I’m glad it uses the brakes rather than the steering, in which case I would have turned it off. But there’s no way to turn it off—not directly. The site calls it Crosswind Assist, but the manual calls it ESP Crosswind Assist. Does turning off the ESP Dynamic Cornering Assist turn off Crosswind Assist? The manual doesn't say and I couldn't figure it out.

Evasive Steering Assist

I'm unsure about this one. It claims to aid in steering away (and around?) an impending collision. I’ve read the manual and spoken to two dealers. No one can give me an answer I totally understand or feel comfortable with. So much can happen in the seconds before an accident; do I trust this to react better than I would? Without knowing more about it, I can’t say. I’d rather turn this off, but you can’t. At least, I don't think you can. Also unclear.

Distance Pilot DISTRONIC

The umpteenth generation of Mercedes’ distance-sensing cruise control. Pretty decent. My only complaints? It let too many cars cut it off in traffic, and was occasionally a poor match to the two-liter inline four. Their relationship was an awkward and buzzy one if speeds weren’t consistent. Also, voluntary deceleration within the system uses engine rather than braking power, which is intended to reduce brake wear (a good thing) but lengthens deceleration and can lead to unexpectedly long high-speed coasting. And confusion. And speeding tickets.


Speed Limit Pilot

Impressive in theory, crude and occasionally dangerous in practice. If the cameras see a new speed limit sign while DISTRONIC is active, the car’s speed will increase or decrease to match it, depending on too many variables to list here.

Let me share just one example about why this doesn't work. If and when the speed limit drops—say, from 55 to 35 mph—you get a rapid and involuntary deceleration, which doesn’t appear to have any relationship with the rear-facing radar, the technology that is theoretically able to detect potential rear-end collisions. The first time I used Speed Limit Pilot, I was almost rear-ended by a semi. Not recommended.

Assistance Graphic/Situational Awareness Display

Displays ADAS warnings, so definitely part of ADAS. But it's misleading. It gives the impression of conveying useful information: if there is a car in front of your E-class, it appears in the display. However, it doesn't change color to indicate that DISTRONIC is locked on to it, nor does it display meaningful information from the state-of-the-art sensor suite. For example, it doesn't show a car not directly in front of you. The lanes are supposed to turn white "when lane markings are detected." In reality, they were almost always white, even when the Steering Assist ran right over them. Occasionally they turn green. What does that mean? Is it because the car now sees clear lane markings and it’s safe to engage Steering Assist? I don't know; the display is not only not intuitive, it's hard to decipher how it works according to the manual. Here's what pages 198 and 199 of the owner's manual say about the system:

Light lane markings: Active Lane Keeping Assist activated

Green lane markings: Active Lane Keeping Assist active

Grey radar waves next to vehicle: Blind Spot Assist activated

Green radar waves next to the vehicle: Blind Spot Assist active

Mercedes claims this the display is not intended for Situational Awareness, and should not be relied upon because it would be distracting. There definitely is a lot going on, but very little to learn from it. Here's one view:

Active Lane Keeping Assist

Drift over lane markers and mild haptic feedback comes through the steering. There are two settings, "Adaptive" and "Standard" — neither of which are effective. Drift too far and the car will brake to correct itself. Not steer—brake. Why not steer? You still drift with braking, you just drift slower.

I tried to test this by allowing the car to drift far enough to observe this alleged braking, but then I realized there’s a much bigger problem, which is Steering Assist.


Steering Assist

Engage Steering Assist with twin pulls of the DISTRONIC stalk and a tiny grey steering wheel appears in the lower left part of the dashboard. This represents standby mode.

If the system feels like it, it will engage, and the steering wheel turns green. This is active mode. In that transition from standby to active, there's no audible notification; likewise, there's no notice when the system disengages.

In real-world testing, paying extra attention to how Mercedes-Benz says the system should be used, I have to say that in anything less than perfect conditions, this system is unsafe. With the system active and with both hands on the wheel, I fought it constantly. Once, when I trusted it enough to take both hands off the wheel to rub my eyes, I barely caught it before it led me right off the road. This is an immature technology. It shouldn't have been released, and I honestly don't know the use-case for it.

(Also, for those who remember this review that suggested Steering Assist had two settings, and one was better than the other—it's nonsense. The reviewer confused the settings for Active Lane Keeping Assist for Steering Assist settings, which don't exist. Call it a placebo effect.)

Active Lane Change Assist

This is meant to automate lane changes while both DISTRONIC and Steering Assist are engaged. It worked maybe 20 percent of the time, though maybe that's a New York City-specific thing. This type of semi-autonomous feature only makes sense to me in a vehicle that can steer itself, and due to the limitations of Steering Assist, I don't think this car fits that bill. You probably shouldn’t use this, but it’s a free country.


Mercedes-Benz's well-deserved safety legacy is rooted in big sedans designed by humorless men with rulers. You know: engineers.

But people who write code are not engineers. Software is as much art as science, and Mercedes, from what I can tell, seems to be shackled not by lack of innovation, but by an old-school engineering culture. Individually, many aspects of the E-Class's ADAS are excellent, and I felt safer using them. But the overarching problem is that few of the functionalities of that ADAS seemed to be talking to one another, as if they were engineered in silos; each one probably passed its specific testing criteria, but the overall product as experienced by an end user was fractured, inconsistent, and unpredictable. So many features, so little fusion.

This is why the E-Class is so frustrating from a safety and semi-autonomy standpoint: It has brilliance in it, but it's not yet a brilliant car. It feels like the very best hardware solution to a problem that requires artful software thinking, and that's not good enough. In this new era, anyone matching Merc's hardware (a tall order to be sure) is one software upgrade from leapfrogging it.

To pull back from the technology focus for a bit, this is a wonderful, comfortable, luxurious car. If I was buying a new car, I'd seriously consider it. But the technology needs work—in some cases, major work.

Luckily, I have a solution, and it only costs $1. First, buy an E-Class with the "Premium 3 Package." Then, buy some black electrical tape. Go into the settings and disable Speed Limit Pilot. Then disable Steering Assist and Active Lane Keeping Assist by pressing the buttons on the left side of the dash; now, tape them over so they stay disabled.

Voilà: You have the safest mid-sized, luxury internal combustion sedan on the road.

For now.

Alex Roy is an Editor-at-Large for The Drive, author of The Driver, and set the 2007 Transcontinental “Cannonball Run” Record in 31 hours & 4 minutes. You may follow him on Facebook, Twitter and Instagram.