For years, Mercedes-Benz has pursued its vision of accident-free driving. The integral safety concept covers all phases of automotive safety — safety when driving and in dangerous situations, protection in the event of an accident and minimising the impact of an accident. Safety is also integrated into the Citaro city buses as standard. The body itself protects the passengers in the event of side impact. In the event of a rear-end collision, the reinforced front end minimises the impact of an accident while protecting the driver.
Safe. Safer. Mercedes-Benz.
From ASR to monitoring the passenger compartment.
Particularly in city traffic, dangers are sometimes unpredictable. This makes it even more essential to take proper measures to prevent an accident. Mercedes-Benz has equipped the Citaro urban bus with many safety features which help in mastering critical driving situations.
Road safety requires drivers to focus fully on traffic conditions. This is why special attention was given to the ergonomic driver's work area. In the Citaro, the driver has comfortable access to all controls and a perfect view of all the instruments. Further convenience is provided by the automatic transmission and the reversing camera. The Opticool windscreen and the separately controlled air conditioning system ensure that the driver is still able to concentrate even when it is hot outside.
A typical situation: a ball rolls onto the street and the children playing with it run out onto the road. A full brake application is necessary. Using targeted electronic brake actuation, the ABS system prevents permanent blocking of the wheels. Additional support is provided via the electro-pneumatic brake control EBS, thanks to which the stopping distance is substantially reduced as the brakes are actuated more quickly and precisely.
Electronic Stability Program (ESP®).
How ESP® works.
The Electronic Stability Program (ESP®) is an active system for increasing driving safety and stability. It makes a noticeable contribution to reducing the risk of skidding during cornering or evasive manoeuvres. This is achieved by specifically controlling the braking forces on each individual wheel in critical, dynamic driving situations, for example if the bus approaches physical limits when cornering. At the same time, the engine output is reduced. A possible "breaking-out" of the bus is thus prevented by the finely metered braking within the limits of the physical possibilities.
Among other things, ESP® monitors the lateral acceleration of the bus. If, on long bends – such as motorway exits – or with rapid lane changes, the bus reaches a critical driving situation, the vehicle speed is automatically reduced so the bus returns to a situation of driving stability. The ESP® is comparable to that used in passenger cars, but is adapted for use in buses thanks to specific extended features.
Acceleration Skid Control (ASR).
ASR prevents the drive wheels from spinning in two ways. On the one hand, ASR minimises wheel spinning through a measured braking intervention. On the other hand, the torque of the engine is regulated via the "electronic accelerator pedal". Even at full throttle, the engine only provides as much power in critical situations as the drive wheels can transmit – a major advantage for controlled pulling away and driving stability.
When starting off, the torques applied and the wheel speeds of the drive wheels are monitored. In this process, torque distribution is controlled in such a way that spinning is prevented. This ensures that optimum power flow is always guaranteed.
ASR helps the driver to minimise the risk of the drive wheels spinning and consequently of the rear of the vehicle (rear-wheel drive) breaking out laterally when accelerating. Especially for high-torque engines, ASR thus provides increased comfort and enhanced safety when pulling away – particularly on roads with varying grip.
Anti-lock braking system (ABS).
How ABS works: there are sensors fitted on all four wheels which detect the rotational speed of each wheel and pass this information on to a central control unit. If the critical point of blocking the wheels is reached, the wheel is stopped at precisely that threshold by pressure variation. The brake pressure can be increased and decreased numerous times in the space of a second.
When braking, all the forces acting on the wheels and the rolling behaviour are continually monitored. The braking forces acting on the wheels are distributed in such a way that no wheel can lock, and the steerability of the vehicle is preserved as far as possible.
In December 1970, Mercedes-Benz presented the world's first electronically controlled ABS – a revolution in driving and road safety. Thanks to targeted electronic braking intervention, the wheels don't lock for long times. The risk of losing steering stability is minimised and, in the case of a full application of the brakes, the vehicle can be steered in the desired direction. ABS technology forms the basis for further developed electronic safety systems such as the electronic stability program (ESP®) or the brake assistance system (BAS).
The Sideguard Assist cornering assistant significantly increases the safety of unprotected road users, particularly in cities, as it helps the driver to recognise critical situations in good time when cornering. The system operates in multiple stages: in the first stage it informs the driver, in the second stage it emits an additional warning. If a moving object is in the monitoring zone to the side of the vehicle, a triangular-shaped yellow LED light goes on in the A pillar on the co-driver's side. It intuitively draws attention towards the situation next to the vehicle. A warning symbol additionally appears on the central display. If the driver initiates or continues an action that could lead to a collision, an additional visual warning takes place: the LED light flashes red with high brightness and then remains on permanently. There is also a vibration warning issued in the driver's seat. Furthermore, Sideguard Assist warns of stationary obstacles in the cornering curve of the bus and can additionally take on the task of a lane change assistant; in doing so, it works in accordance with the same warning cascade.
Preventive Brake Assist.
With the Preventive Brake Assist feature, Mercedes-Benz is offering the first Active Brake Assist for city line buses worldwide. The assistance system warns of a potential collision with moving pedestrians as well as stationary or moving objects and automatically initiates a braking manoeuvre with partial braking in the event of an acute collision hazard. Warning cascade and braking intervention are designed for use in city traffic. In the event of an imminent collision with pedestrians and with moving or stationary objects, the Preventive Brake Assist warns the driver visually by a red illuminated triangle with a vehicle symbol in the central display as well as acoustically, while initiating partial braking. This is held until either the driver intervenes or the bus comes to a stop. The platform for the Preventive Brake Assist is a new generation of radar technology: the radar system continuously scans an area of up to 250 metres in the lane in front of the bus and works reliably even at night and adverse weather conditions.
The cornering light function.
The cornering light function provides significantly improved safety for night-time driving when turning corners at poorly lit junctions, at roundabouts or when manoeuvring and reversing.
The cornering light function is activated automatically at speeds of up to approx. 40 km/h if the main headlamps are on, the turn signals are actuated or the steering wheel is turned. One of the two front fog lamps is switched on to illuminate the area to the side and front of the vehicle which is not lit by the main headlamps. The intelligent electronic system switches the dimmed cornering lights on or off. This gives the eye a chance to adjust to the changed light situation.
The unique ATC articulation limiter system in the Citaro G.
One of the core elements of the Citaro G is its turntable and the control system especially developed and thoroughly tested by Daimler researchers. The maximum angle between the two sections of the vehicle at full lock is 54.5 degrees. The unique ATC (Articulated Turntable Controller) is a new, highly sophisticated articulation limiter system especially developed by Mercedes-Benz. ATC sets new standards for the driving dynamics and safety of articulated buses:
ATC (Articulation Turntable Controller) jackknifing protection system – functions and advantages.
The ATC driving dynamics control regulates the hydraulic damping of the articulation swiftly and, most importantly, perfectly in line with requirements, depending, among other things, on the steering angle, the articulation angle, vehicle speed and load. ATC has access to the data of the CAN Data Bus.
The result: Whereas the conventional high basic articulation damping leads to a strong tendency to understeer in curves and to increased tyre wear on the front axle, this articulation operates virtually freely in a normal stable driving situation and is damped only by the friction of the component elements.
Tyre pressure monitoring (TPM).*
The tyre pressure monitoring system warns of drops in tyre pressure in one or more tyres before and during the journey. It monitors the pressure of all tyres and shows the readings on the multifunction display.
Correctly inflated tyres last longer and above all enhance safety when driving. The tyre pressure monitor can help to recognise falling pressure in one or more tyres when driving and avoid potentially serious consequences.
For this purpose, a sensor on the tyre interior measures air pressure and temperature. This data is transmitted by radio at regular intervals to a receiving aerial on the underfloor and forwarded to the control unit. Tyre pressures can also be shown in the multifunction display if required.
Over the course of several months, tyres gradually lose air through diffusion. The tyre pressure monitor displays a message in good time to prompt the driver to correct the pressure. If there is a significant drop in pressure when driving, a yellow warning light comes on and a warning message is displayed, enabling you to take appropriate action.
Monitoring of the passenger compartment.
The video monitoring cameras installed can keep track of the events taking place on the bus. A video monitoring system can not only improve the sense of safety for the bus driver and passengers, it can also record troublemakers who commit acts of vandalism or violence.
The data is transmitted to the monitor in the bus driver's workstation. The bus driver can then better view and evaluate events occurring in the passenger compartment and, if needs be, react in the event of danger.
The vehicle is labelled with pictorgrams to inform passengers that the vehicle is video-monitored. Video monitoring enhances the subjective sense of safety for driver and passengers and thus the appeal of using public transportation. The video monitoring system is an optional extra.
More information on the video monitoring function and data storage is available from our bus sales consultant.
* Optional equipment