Safety and Security: Mercedes-Benz S550

Associate Editor

This sexy strongbox of a sedan wowed the judges for several reasons: It comes loaded with more goodies than Santa's sleigh; the S-Class practically drives itself; and — let's be honest — the $100,250 sticker made the judges feel like royalty during their brief reigns behind the wheel.

The S-Class is as much about safety as it is luxury. A number of safety innovations first appeared on this model: computer-controlled Antilock Brake System (1978); Supplemental Restraint System, of which front air bags were one component (1982); and Electronic Stability Program (1996).

Essentially, ESP works invisibly to help keep the car going where the driver points it. Using electronic sensors and computer logic, the system measures whether the car is going in the direction it is being steered. If there's a difference, the system corrects with split-second speed by applying one of the left or right-side brakes. ESP uses the angle of the steering wheel and the speed of the four wheels to calculate the path being steered, and it gets electronic signals about lateral acceleration and vehicle yaw rate to measure what the car is actually doing. (Yaw rate describes the speed at which a vehicle rotates around its vertical center axis.)

Mercedes' Pre-Safe system debuted in the '02 S-Class. The system tightens the front seat belts moments before a possible impact, and the front passenger seat (and optional power rear seats) move to positions that can provide better protection. If the system senses an impending rollover, the sunroof also closes. Side windows close to provide better support for the window curtain air bags, and seat cushions can inflate to offer greater lateral support for occupants and supplement the side air bags.

Distronic cruise control that maintains a preset following distance behind the vehicle ahead has been replaced by the optional "Distronic Plus" system. Integrated with Pre-Safe, this latest radar-based system operates at speeds up to 125 mph and can be especially useful in stop-and-go traffic. When set, the system automatically accelerates and brakes (up to 40% of its capacity) to help regulate the car in traffic when the selected speed cannot be maintained.

Short-range radar with a frequency of 24 GHz sweeps the first 33 yards in a fan-shaped 80° pattern, working in tandem with a narrower 9° beam of longer-range 77-GHz radar. The two radar frequencies complement each other to cover a range of more than 160 yards.

The system can identify if the car is gaining too quickly on vehicles ahead, and sounds a warning and adjusts brake pressure, which is applied as soon as the driver steps on the brake pedal. At all speeds, the system monitors other vehicles ahead and moving in the same direction.

In the early 90s, Mercedes engineers conducting simulator tests discovered that many drivers don't push the brake pedal hard enough in emergency braking, a discovery that led to the development of Brake Assist. The company claims that vehicles equipped with Brake Assist are involved in 26% fewer accidents. While Brake Assist operates independently of the antilock brakes, it relies on ABS to prevent wheel lockup during full-brake-force application.

An enhanced version of Brake Assist not only supplies braking assistance in emergencies, but also measures the distance to the vehicle ahead and adjusts brake pressure if the driver doesn't brake hard enough.

While conventional Brake Assist is only triggered by the driver's reflex reaction on the brake pedal, BAS Plus also considers the closing speed of the vehicle ahead based on radar signals. The system provides visual and audible warnings if it determines the vehicle is about to run into the vehicle in front and calculates the brake force needed to prevent the crash. This additional force is available the moment the driver steps on the brake pedal.

If the driver does not react to BAS Plus warnings and there is imminent danger of an accident, the system triggers automatic partial braking and decelerates the S-Class at up to 0.4 g (approximately 4 m/sec ² ). This is equivalent to around 40% of the maximum braking performance. If the driver immediately activates the brake, maximum braking force is available, and — depending on the situation — it may be possible to prevent the accident at the last moment. If not, the Pre-Safe brake reduces the severity of the impact.

As the manufacturer explains, the Pre-Safe brake is an "assistance system" that helps the driver at critical moments. Even during automatic partial braking, the driver retains responsibility for the vehicle and decisive action on his or her part can help prevent a collision.

Development of the Pre-Safe system was based on findings that about two-thirds of all accidents are preceded by events that indicate the possibility of an impending crash, such as skidding, emergency braking, or a sudden evasive maneuver — all of which can provide several seconds of valuable advance warning.

"While present protection systems such as air bags, window curtain air bags, and belt tensioners must ensure safety in a matter of milliseconds, accident recognition can be measured in seconds. Making use of this relatively long interval opens up new dimensions in occupant protection," says Dr. Rodolfo Schoeneburg, head of Mercedes-Benz passive safety development.

Looking ahead, engineers fore-see subsystems such as knee protection that moves out from the lower dash before a frontal impact. It completely retracts if the accident is avoided. Door panels that move in toward the occupants before a side impact may be on the horizon. Engineers also envision protective systems that adapt to individual occupants. Drivers and passengers might enter their height, weight, and gender, and a computer could use the data to customize seat positioning, seat-belt tensioning, and air-bag inflation rate.

Distronic Plus incorporates 24-GHz radar-based Park Assist. This option uses six obstacle detectors behind the front and rear bumpers. When reverse gear is engaged an optional rearview camera just above the license plate displays the area behind the car on the Command screen. Lines on the display change with steering inputs to assist the driver in parking.

Another technology debuting on the '07 S-Class is Night View Assist, an option that claims to extend the driver's sight to nearly 500 ft at night. In contrast to passive systems that rely only on thermal imaging, this system bathes the road ahead with infrared light from two projector beams mounted in the headlights. An infrared camera in the windshield receives reflected images and displays them in a high-resolution display on the instrument cluster. The result is similar to a highly detailed black-and-white image.

The centerpiece of the dash is the 8-in.-high display for the Command system. It is operated by an intuitive controller on the lower center console. Instead of requiring occupants to use the Command system exclusively, many vehicle controls are also accessible by conventional hard keys, the steering-wheel switches, and optional voice control.

The Global Positioning Satellite (GPS) based nav system has map information for all of North America on a 20-Gbyte hard drive. The system uses an onboard computer, satellite positioning, a gyro system for detecting direction changes, and yaw and wheel-speed sensors to pinpoint the car's position and progress. Based on mapping information, a microprocessor calculates the route, which is shown on the dis-play, and a voice provides turn-by-turn directions.

The standard voice-control system lets drivers use the telephone, audio, and nav systems. Voice commands are acknowledged verbally. The system is adaptive, so it can "learn" specific voices.

Another amenity is a slot in the dash that accepts a PCMCIA card. These cards never need to be charged, and some versions can hold up to 1,500 digital songs. Users can select titles with the steering wheel controls. How cool is that?

The new S-Class comes with a seven-speed automatic transmission. A small lever on the right side of the steering column serves as an electronic gear selector — lift the stalk up for Reverse, push down for Drive, and push a button on the end for Park. Standard Airmatic air suspension lowers the car at higher speeds to reduce drag.

Located by the center console between the seats, a turn-and-push controller selects the Command main and submenus. The aluminum knob is power assisted by a small electric rotor that also provides tactile feedback. Behind the controller, a hand rest flips up to reveal a numeric keypad for the cell phone.

If all this technology (not to mention $100K) is a bit rich for your palate, a stripped-down version can be yours for $85,400.