Safe, efficient and excellently equipped – a test drive of the new Setra S 531 DT double-decker bus through northeastern Europe

The new Setra S 531 DT from the TopClass 500 model range is Setra's flagship coach. Measuring a stately fourteen metres in length and four metres in height, with a permissible total weight of 26 tonnes, the double-decker bus combines safety with comfort, efficiency and versatility

  • Journalists test the new Setra S 531 DT between Berlin and Tallinn
  • More safety for the most vulnerable road users: Sideguard Assist and Active Brake Assist 4
  • Maximum efficiency: optimised aerodynamics and a perfectly tuned powertrain reduce fuel consumption
  • Great versatility: whether for vacation trips, long-distance bus services or inter-urban traffic – the new double-decker is an all-purpose bus
  • Comfort for all passengers: high-class seats, a light interior, easy-access staircases, a modern washroom and an innovative fragrancing system
  • A modern and distinctive design that follows the tradition of Setra’s brand claim “Sign for Excellence”

The new Setra S 531 DT from the TopClass 500 model range is Setra’s flagship coach. Measuring a stately fourteen metres in length and four metres in height, with a permissible total weight of 26 tonnes, the double-decker bus combines safety with comfort, efficiency and versatility. For the “Test Drive Northeast Europe” that takes place from 19 to 23 March 2019, the vehicle is available in cosmos red metallic with top-class equipment. Selected journalists will test the bus first presented to the public at the IAA 2018 on a five-day, nearly 2000‑kilometre journey from Berlin to Tallinn.

Whoever sits behind the wheel of the bus among the nearly two dozen reviewers will get to enjoy the S 531 DT’s high-quality TopClass cockpit with its sophisticated ergonomic design. Meanwhile, the other participants can relax on the comfortable, generously spaced “Setra Voyage Plus” seats. Participants will have the opportunity of exchanging their views in the double-decker’s luxurious lounge area.

In this test drive configuration, the S 531 DT offers space for 78 passengers. The test vehicle will be fully loaded with ballast tanks in order to convey the most realistic driving impressions and fuel consumption measurements.

A world premiere for a bus: the new Sideguard Assist warns the driver of potentially dangerous accidents while turning off and changing lanes

Turning manoeuvres to the right in city traffic are among the most challenging tasks for a bus driver: In front, the driver has to pay attention to traffic lights, road signs as well as oncoming and cross traffic, and at the same time has to keep an eye out for pedestrians and cyclists to the left and right. What’s more: The traffic situation can change in the blink of an eye. For this reason, Setra offers the new turning assistance system Sideguard Assist with person recognition in its new S 531 DT. The system can recognise both stationary objects such as traffic lights, road signs and bollards in the warning zone to the right of the bus as well as moving objects such as pedestrians, cyclists and other vehicles. This represents a big step forward for the protection of the most vulnerable road users.

Sideguard Assist uses a method of operation consisting of several levels: If a moving or stationary object is in the surveillance zone, the system first issues a visual warning to the driver. For this purpose, a triangular LED on the exterior mirror on the co-driver side lights up yellow. If the sensors detect the risk of a collision, the LED flashes red with increased brightness several times, and then lights up in red permanently after two seconds. In this case, the driver’s seat also vibrates to provide an additional warning.

When turning, Sideguard Assist warns the driver about dangerous situations in so-called tractrix curves in the speed range of up to 36 km/h. In addition, the system also supports the driver during changes of lane to the right at speeds above 36 km/h. In such situations, the driver is also warned about objects on the co-driver’s side. This happens both while indicating as well as during a steering motion to the right. Therefore Sideguard Assist supports the change of lane for example on multi-lane roads or while overtaking a cyclist out of town.

Radar sensor technology is the centrepiece of Sideguard Assist, with two short-range radar sensors installed in the front wheel arch on the co-driver’s side. The lateral surveillance zone is 3.75 metres wide. the system is geared to cover the entire length of the bus plus an additional two-metre stretch to both the front and the back. At speeds of more than 36 km/h, these stretches are extended to up to five metres at the front and up to fifteen metres at the back. Important to note: For all situations in which Sideguard Assist issues warnings, the driver remains fully responsible for the vehicle.

Active Brake Assist 4 in the S 531 DT: now with person recognition and an improved radar system

Coaches with emergency braking assistance systems can not only reduce the impact of a major accident, but within the range of what’s physically possible, they can even prevent collisions in many cases. In the meantime, the Advanced Emergency Braking System (AEBS) has become legally required for Class 3 buses and has to ensure a significant speed reduction if the vehicle is headed directly towards both moving and stationary obstacles. The new Active Brake Assist 4 greatly surpasses these requirements. The S 531 DT is equipped with the emergency braking assistance system as a standard.

The outstanding new feature of Active Brake Assist 4 is the person recognition: The system warns the driver about a collision with moving pedestrians, and in addition initiates partial braking automatically. This gives the driver the possibility of avoiding the collision by means of maximum full-stop braking or a steering manoeuvre. But unlike during braking manoeuvres while the vehicle is headed towards moving and stationary obstacles, warnings are not issued in series during partial braking when the vehicle is moving towards moving pedestrians: Instead, both the acoustic and optical warning signals as well as partial braking are initiated at the same time. These automatic warning and braking responses of person recognition in Active Brake Assist 4 are in effect up to a speed of 50 km/h.

Like its previous version, the new Active Brake Assist 4 also supports its driver in three steps in situations where there is a risk of a rear-end collision: When the system recognises a stationary or slower-moving vehicle in front, initially it sends the driver a visual and acoustic warning. If the driver does not respond appropriately, the system initiates a partial braking manoeuvre with around fifty percent of maximum braking power in a second step. And if there is still a risk of a collision despite these measures, the system autonomously applies maximum full-stop braking. This brings the bus to a halt if necessary, within the system’s limits. In addition, the hazard warning lights are activated.

Active Brake Assist 4 utilises a new generation of radar technology. These are so-called multi-mode radars that electronically scan the area, and are greatly improved in terms of range and performance compared to their predecessors. This new type of radar has already proven itself in current Mercedes-Benz car and truck models – exemplifying the fruitful collaboration within the company.

Radar systems have the advantage of working well independently of lighting conditions, and for the most part independently of weather conditions. The radar system in Active Brake Assist 4 determines distance and relative speed to the vehicle driving in front with extreme precision. The long-range radar used by the emergency braking assistance system now operates independently of the driving level configuration, and can constantly adapt to changes in vehicle inclination that can, for example, be caused by different loading or chassis conditions. It identifies vehicles and obstacles in a straight line in front of the vehicle within a range of 250 metres. Pedestrians are recognised at a distance of up to 80 metres, cyclists and moped drivers at up to 160 metres’ distance.

The short-range radar has a range of up to 70 metres and is able to identify vehicles and moving pedestrians to the side of the vehicle thanks to its wide beam width of 120 degrees. Its detection range however also depends on the surrounding topography, course of the road, weather conditions as well as external influences such as pedestrians that are concealed or rapidly moving into the traffic area.

All things considered: The bus driver remains solely responsible for all driving manoeuvres and the operation of the vehicle. He can always override the system whenever needed, either through a kick-down, by steering or through an emergency full-stop braking manoeuvre. But if the driver does not brake sufficiently, the braking intensity provided by Active Brake Assist 4 will be put into effect.

Even greater safety thanks to LED headlamps and a fire extinguishing system as standard – the voluntary pendulum impact test has been passed

Apart from Active Brake Assist 4 and Sideguard Assist, which on the world’s bus market are only available from Daimler Buses, there are many further tried and tested driver assistance systems in the S 531 DT: the Electronic Stability Program (ESP), the adaptive cruise control, Lane Assist, Attention Assist as well as the tyre pressure monitoring system. What’s new, however, are the LED headlamps as standard, which offer significantly more brightness than conventional halogen lights and therefore illuminate the road even better. The light of the new LEDs reduces eye fatigue, as it is more similar to natural daylight. The LEDs’ durability and nearly undiminished light intensity throughout their entire lifespan also contribute to increased safety.

Also part of the new S 531 DT’s standard equipment is a TÜV-certified (German Technical Inspection Authority) automatic fire extinguishing system. And that’s before this feature becomes a legal requirement for coaches in June 2019. This system uses detection lines that initiate the extinguishing process in response to a pressure drop, which is caused by major overheating. The extinguishing fluid is pressed through the nozzles of the distribution system, and sprayed out in the form of high-pressure water mist in the engine compartment. This causes the displacement of oxygen within fractions of a second, hereby removing the basis for the fire. At the same time, the surfaces of the components are cooled, preventing the fire from being re-ignited. The pipeline for the extinguishing fluid runs through the entire engine compartment. The individual nozzles are specifically aimed at the components that reach higher temperatures, such as the turbocharger, oil filter module and auxiliary heater.

Primarily, Setra focuses on the prevention of accidents by means of active safety systems such as Active Brake Assist 4 and Sideguard Assist. However, should an accident still occur, both driver and passengers profit from the best possible passive safety. For instance, the S 531 DT incorporates its previous model’s reinforced framework, and therefore voluntarily fulfils the requirements for passing the pendulum impact test as specified in the ECE-R-29 guideline. In addition, Setra provides rescue services with rescue data sheets for all of its buses online.

Maximum efficiency: optimised aerodynamics and a perfectly tuned powertrain reduce fuel consumption by up to ten percent

Depending on its field of application, the new S 531 DT scores points with a fuel consumption which has been reduced by about seven to ten percent compared to the previous model. One major reason for this is the thoroughly optimised aerodynamic performance. At the front of the double-decker bus, strongly curved windscreen panels and large edge radii allow the air stream to gently flow around the vehicle, while at the rear recesses and airflow break-away edges guide the airflow in a targeted manner. The engineers have also made sure to implement even the smallest improvements to the aerodynamic performance: For example, the windscreen wiper of the upper decks is upright in its resting position – an idea derived from motor sports. The result of these measures is an air drag coefficient of Cd = 0,35 – the best value in the double-decker bus segment.

The new S 531 DT’s fuel consumption is also low due to the fuel efficiency of its standard 12.8-litre OM 471 engine. The engine delivers an output of 375 kW (510 PS), and with its economical and environmentally friendly, Euro‑VI‑compliant exhaust gas aftertreatment, it propels the double-decker bus in a quiet, efficient and future-proof way. Its maximum torque of 2500 Nm is already available at 1100 rpm. The GO 250-8 fully-automated transmission ensures high driving comfort, and its precise gear selection and short shift times also contribute to the vehicle’s overall cost-effectiveness.

Versatility for the widest range of applications: The new Setra is an all-purpose bus and leaves space for individual preferences

Whether for holiday tours, bistro buses, long-distance or inter-urban service buses – the Setra TopClass S 531 DT covers all possible uses for a bus of its format. And, typical for the Setra brand, there are numerous options for customising the double-decker bus’s seating options as well as other aspects of the equipment. In addition, there are also variable options for the use of the lower deck: Optionally the ground-level platform, located on the right in the direction of travel, can be omitted thanks to an entirely new design. This further increases versatility by allowing the installation of wheelchair bays as well as bistro-bus equipment. For use on inter-urban service buses, it’s possible to install an interchangeable platform with space for pushchairs. And for regular tourist traffic, this frees up space for regular seating.

The S 531 DT’s versatility is also evident in the cockpit: Buyers can choose between the elegantly functional cockpit from the Setra ComfortClass 500 and the luxurious cockpit from the TopClass 500 series. And of course, the travelling companion can take a seat on their own comfortable chair.

High-quality, comfortable interior: light colours, easy-access staircases, a modern washroom and an innovative fragrancing system

With its modern design and ample amounts of light, the bright interior of the new Setra TopClass S 531 DT feels open and spacious. The staircases connecting the upper and lower decks are eye-catching: Glazed from the outside, they are covered with translucent acrylic panels on the inside. Even-spaced, two-coloured steps with customisable lighting, landings and continuous handrails ensure safety while ascending and descending the staircases. In addition, the bow in the upper deck has been completely redesigned.

In the S 531 DT, passengers settle down in comfortable “Setra Voyage Plus” seats with dark evogrey seating surfaces whilst the side bolsters and back are in carbon red. The seats are equipped with height-adjustable comfort headrests in composition black. And additional design elements in Vincent Prestige red add an even more colourful note to the interior of the test vehicle.

An optional fragrancing system creates a pleasant atmosphere inside the new Setra double-decker bus: When the ignition is switched on or the front door opened, or while the door is standing open, a fragrance dispenser automatically emits a subtle and understated fragrance. Available options are six different fragrances ranging from fresh and athletic to heavy and leather-like. The main components for this system come from the Mercedes-Benz S-Class.

A Coach MediaRouter enables passengers to connect their mobile devices to the Internet via Wi-Fi at any time. The S 531 DT’s galley also enables passengers to be well-provided for on a culinary level. The barrier-free washroom has been completely redesigned: It is diagonally arranged, in other words in a particularly space-saving way. With its glossy white furnishings and LED lighting, it’s reminiscent of a modern bathroom.

Distinctive exterior design: clear lines as a “Sign of Excellence” – and as an expression of optimised aerodynamics

The new double-decker S 531 DT has a both modern and distinctive appearance. Its “face”, with its dark front panel and silver brand lettering, is unmistakably derived from the tradition of the tried and tested TopClass 500 model range. The two seamlessly dovetailed windscreen panels, which are divided only by a discreet aluminium brace, are a new feature for a double-decker. The vertically positioned windscreen wiper in the upper deck is another innovation that not only looks good, but also improves aerodynamic performance.

The designers have also updated and refined the brand-typical “La Linea” aluminium trim on the side panel. It now stretches horizontally along the roof edge. The extensive glazing is highlighted by a counter-sweep at the level of the rear stairs. This aluminium-framed design feature conveys a sense of dynamism. The upper deck’s panelling floats on the glass like an island. Below that, an aluminium logo plaque above the front wheel arch provides a break in the waistrail on the lower deck.

The rear is framed by side fins with airflow break-away edges as well as the tail lights of the 500 model range. Both of the engine’s ventilation grilles are now connected to each other for the first time in the Setra TopClass S 531 DT. Furthermore, the black grille from the integrated TopAir air conditioning system adds another style feature. Below the rear window, we can see the chrome-plated logo panel with its brand-name lettering from the TopClass 500 series – the perfect conclusion to a truly eye-catching bus design.

Source: Daimler

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