Mercedes takes its biggest step yet toward the autonomous car in its revised flagship sedan. We take it for a test drive.
S-Class allows autonomous steering for up to 30 seconds.
STUTTGART, Germany – Speeding fines are set to become a thing of the past for drivers of the upcoming facelifted Mercedes-Benz S-Class following a decision to equip the upmarket sedan with an extended range of driver-assistance systems, including newly developed Active Distance Assist that provides fully autonomous acceleration and braking over any journey programmed into its upgraded navigation system.
Part of a revised Distronic Plus adaptive cruise-control system Mercedes says eventually will filter down into all of its models, the new driving function promises set-and-forget speed-limit peace of mind by autonomously controlling throttle and brake inputs and strictly adhering to both posted and temporary speed limits, whether in an urban environment, on country roads or on the highway.
When engaged, Active Distance Assist allows the driver to ignore the pedals for extended periods. Laws in many markets still require drivers to steer. However, the job of accelerating and braking as well as scanning road signs for changes in speed limits and other warnings is taken care of and autonomously acted upon by the new S-Class that makes its public debut at next month’s Shanghai motor show and goes on sale in the third quarter.
The optional driver-assistance system, accessed via buttons on a newly designed multifunction steering wheel rather than on Mercedes’ traditional cruise-control stalk, relies on an upgraded stereo camera mounted inside the windshield, with the two lenses moved farther apart for improved definition, to scan road signs.
It also uses an improved long-range radar system that operates at up to 820 ft. (250 m) in front of the car to support the driver and autonomously brake the S-Class to standstill should it detect an obstacle.
The system can adjust speed based on digital mapping data incorporated in the upgraded Comand navigation and infotainment system.
The mapping data, provided by the HERE joint venture with Audi and, is described by Michael Hafner, head of automated driving and active safety at Mercedes-Benz, as being “significantly more intelligent” than that of previous systems.
In a development touted as a key step on the way to fully autonomous driving, the Active Distance function uses digital-mapping data to reduce speeds in curves and at roundabouts, junctions and toll booths, coming to a complete stop when necessary and autonomously speeding up again when both road conditions and speed limits allow.
The character of the autonomous functions can be altered in three modes via the Dynamic Select system. Eco provides a conservative driving style for maximum fuel savings; Comfort aims for more serene progress; and Sport is programmed to maximize acceleration and braking. Cornering speeds also are varied between the three modes.
Mercedes’ latest autonomous-cruise-control function regulates the following distance from other vehicles at speeds up to 131 mph (210 km/h). To maximize fuel economy in Eco mode, it engages the coasting function during periods of trailing throttle, taking into account the speed limit and autonomously braking to ensure it isn’t exceeded.
Coupled with a revised Active Steering Assist function, the Active Distance technology provides autonomous steering for periods of up to 30 seconds. Hafner says the software controlling the autonomous steering has been reworked extensively, providing greater accuracy and improved fluidity.
Supporting Mercedes’ latest Distronic Plus system is a new series of graphics, both within the instrument cluster and the optional head-up display unit.
Additional driver-assistance systems in the facelifted S-Class include automated lane changes, emergency braking, brake assist and remote parking functions already offered on the E-Class.
So what’s it like?
As we set off in the S-Class for the first time with all its various driving-assistance systems switched on, the overriding impression is just how far Mercedes has come to delivering on the promise of full autonomous-driving capability.
While the German carmaker has yet to provide the upper-luxury sedan with a fulltime autonomous steering function due to laws prohibiting such a system on European roads, the combination of its new Active Distance Assist and Active Speed Limit Assist functions nonetheless represent a significant step toward the driverless mobile-lounge-like qualities touted by recent concepts such as the F015 Luxury In Motion.
With a route programmed into its updated Comand Online navigation system, the S-Class gets under way with a gentle nudge of the throttle by the driver. From there, it autonomously accelerates and brakes its way out of the Mercedes technical center on the outskirts of Stuttgart.
Using information gathered by its newly engineered stereo camera, long-distance radar and the digital mapping data from the navigation system, we spend almost an hour heading along a section of a 6-lane autobahn, winding country roads and urban streets.
Impressively, the only action required by the driver is an occasional tweak of the ʼ17 S-Class’ new multifunction steering wheel and an application of the brakes at stop junctions.
With the new Mercedes able to accelerate and often brake on its own, including around corners and through roundabouts, stress on the driver clearly is reduced. As a further advantage, the speed of the heavily disguised prototype S-Class we’re in never rises above the prescribed limit for the entire journey.
What really impresses is the predictive element Mercedes has engineered into its latest Distronic Plus system.
As we exit an autobahn, the S-Class autonomously applies braking force within the exit lane, recognizing the corner ahead and adjusting our speed accordingly. When we reach the corner, sufficient speed has been scrubbed off to enable the driver to confidently turn in before the car accelerates to the 44-mph (70-km/h) limit without the driver’s foot coming anywhere near the accelerator.
In another example of its predictive capability, the new Distronic Plus system applies braking force while entering small towns, ensuring the speed of the car is perfectly matched to the posted limit.
It also identifies temporary speed limits in construction zones, even on signs that are partly obscured.
But while representing a big advance from the former Distronic Plus system, the Active Distance Assist and Active Speed limit Assist systems are not quite perfect. The sign-scanning software cannot yet differentiate between varying speed limits where the roadside sign denotes a certain time of day for one limit and then a second time of day for another.
“We’re working on it,” Hafner says. “But the complexities are enormous and these things simply take time.”
We also noticed the S-Class fails to come off the throttle and adjust speed when we pass a temporary oil-spill sign – something you might expect an alert driver to do.