IAA premiere: the fascinating Setra S 531 DT double-decker bus

• Design: modern and surprisingly distinct appearance
• Prime example of aerodynamic and fuel efficiency
• Variability: the new Setra is a bus to meet all needs
• Comfort: bright interior, convenient stairs, innovative wash room
• Safety: Active Brake Assist 4, Sideguard Assist

Maximum efficiency and variability, supreme comfort and the ultimate in safety: the Setra S 531 DT double-decker bus of the TopClass 500 again sets standards in its class and will celebrate its premiere at the IAA. With superlative aerodynamics, this impressive touring coach is all set to establish new fuel efficiency records in its segment. With its variable lower deck, it covers the entire scope of applications in touring and line service. The interior boasts an impressive standard of comfort. Finally, the new assistance systems Active Brake Assist 4 and Sideguard Assist enhance the already high safety level even further. All of this is cloaked in a fascinating design with its own distinct stamp.

Design: modern and surprisingly distinct appearance

The new double-decker bus belongs to the Setra TopClass 500. Within the 500 model series, it is nevertheless in a class of its own, on account of its broad range of applications and its diverse scope of equipment and variants. This is documented by its modern and distinct appearance. The Setra's face with its dark front panel and silver brand lettering clearly originates from the TopClass 500. As a new feature, the two windscreens are seamlessly joined together and structured by an aluminium bar.

On the sidewall, the designers have adapted the brand's hallmark "La Linea" aluminium strip, which now extends horizontally along the edge of the roof. The extensive glazing is highlighted by a counter-sweep at the level of the rear stairs, which adds a dynamic touch and features an aluminium surround. The panelling of the upper deck now appears to hover like an island on the glass. Underneath, an aluminium logo plaque above the front wheel arch provides a break in the waist rail on the lower deck.

Side fins with airflow separation edges and the tail lamps of the 500 model series frame the rear end. The ventilation grilles of the engine are interconnected. Above these, the black grille of the integrated TopAir air conditioning system makes its mark. The chrome-plated logo plaque featuring the brand logotype from the TopClass 500 catches the eye under the rear window – a perfect finishing touch for a spectacular bus.

Prime example of aerodynamic and fuel efficiency

Form and function go hand in hand on the new double-decker bus. It is a prime example of aerodynamic. With a drag coefficient of C_d = 0.35, it sets a new benchmark in its segment and thereby lays the foundation for maximum fuel efficiency: Depending on the type of use, the Setra S 531 DT is another seven to ten percent more fuel-efficient than its already economical predecessor. Depending on the mileage driven, this adds up to savings of several thousand litres of fuel annually. This means that the new double-decker bus saves fuel and thus money on every mile of motorway driving, reducing emissions and saving resources. At the same time, the extensive aerodynamic detail work minimises wind noises, clear added comfort for passengers and driver.

The two windscreens are seamlessly joined and feature a more prominent curve. The air is better able to flow around large edge radii. Where needed, for example on long-distance regular-service buses or inter-city buses, a destination indicator is installed behind the lower windscreen. Virtually no gaps remain between the body and the flush-closing doors and the driver's window. The rain gutters above the doors only fold out when the doors are opened. The panelling of the underbody in the front-end assembly is also effective. The leaf-shaped arms of the side mirrors have also been aerodynamically optimised.

The aero windscreen wiper system plays a major role in reducing the vehicle's aerodynamic drag. On the lower deck, Setra employs the proven Aquablade windscreen wipers from the 500 model series. These are flat-blade wipers with integrated water channel and no disturbing frame. The two-arm wiper system on the upper deck has been replaced by a centrally positioned single-arm wiper with flat-bar wiper blade.

The Setra's newly designed rear end has also been developed with due regard to aerodynamic aspects. The roof has been fitted with an airflow-optimised flue. The new corner pillars in the form of fins are recessed at the sides and feature sharp airflow separation edges. These two measures route the airflow in a defined manner, thereby reducing turbulence as well as soiling.

The double-decker bus is furthermore lowered imperceptibly by 20 mm from a speed of 95 km/h. In addition to the comprehensive fine-tuning work on the body, the developers reduced the cross-section and thus the aerodynamic drag in this way.

Variability: the new Setra is a bus to meet all needs

Holiday travels, long-distance regular-service routes, stylish bistro buses, inter-city lines – the new Setra covers all conceivable types of use for a bus on this scale. The lower deck suitable for various purposes provides the basis for this, together with the scope for individual appointments and seating characteristic of the brand. Thanks to a completely new design, the platform on the bottom deck on the right as seen in the direction of travel can be omitted if the customer so desires. This results in new options: wheelchair bays, installations for bistro buses, a demountable platform with pram area for inter-city lines or, with platform, the classic seating for touring purposes. When maximum seating capacity is desired, e.g. for operation on inter-city routes or internal company transport services, Setra also delivers the double-decker bus without kitchenette and wash room, with a full seating complement of up to 93 seats.

The variety is also manifest in the cockpit: customers can choose between the elegantly functional cockpit from the Setra ComfortClass 500 and the luxurious cockpit from the TopClass 500.

Comfort: bright interior, convenient stairs, innovative wash room

With plenty of light and a modern design, the interior of the new Setra offers a generous sense of space. A factor in this is the greige colour of the trim for window posts and interior ceiling, a friendly and bright blend of grey and beige.

High-quality materials, comfortable and functional appointments – the passenger compartment of the Setra double-decker bus is of high standard. A crucial component is the comfortable and highly variable seating with its broad range of fabrics and the "Composition" leather-fibre material, as well as the optional luxury head restraints.

Like its predecessor, the new double-decker bus offers two variants for the two stairways. While the rear stairs are always located aft of door two, operators are free to choose the position of the front stairs. A popular choice in tourist transport is to have the stairs positioned on the left behind the driver, as seen in the direction of travel. For use on long-distance scheduled services, operators prefer the stairs to be positioned in the direct vicinity of the front entrance, on the right as seen in the direction of travel, on account of the faster passenger flow.

Glazed on the outside, the stairs to the upper deck on the inside feature panelling made of translucent acrylic plastic. Evenly spaced two-tone steps with individual lighting, landings and continuous handrails give passengers a sense of safety when going up and down the stairs.

The wash room in a totally new design is also worthy of note. Its installations are arranged diagonally, making maximum use of the available space. In addition, there is the significantly increased standing headroom. The gleaming white upper areas of the furnishings and the pleasant LED lighting are reminiscent of a modern bathroom.

A double-decker bus has a second cockpit - the cockpit for the passengers in the first row on the upper deck. A totally new second cockpit has been designed for the new Setra TopClass S 531 DT. Like the cockpit on the lower deck, its counterpart on the upper deck also sports a two-tone colour scheme: The top and fronts have a dark finish, while the centre section is in greige.

Luggage compartment capacity slightly increased, additional stowage compartments

As on the predecessor model, the luggage compartment with a practical smooth surface of the new double-decker bus is accessible via a large rear-end door and side stowage flaps. A space-saving side step in place of the previous step has allowed a slight increase in the space with the volume now being 8.4 m³.

At the same time, this measure has also created space for a tool compartment and an additional practical stowage compartment in the entrance. There is also a new stowage compartment in front of the front axle, under the driver's cockpit. On top of this, if required, there are also the usual stowage options on the right between the axles, beneath the platforms.

The unparalleled economic efficiency of the double-decker bus

The latest most economical and robust generation of the OM 471 engine demonstrates that a good thing can still be improved upon. Suitably prepared, the new double-decker bus is all set to begin its working life with a perfectly coordinated and well-proven powertrain from a single source - Mercedes-Benz: an OM 471 engine rated at 375 kW (510 hp), a fully automated GO 250-8 PowerShift bus transmission, and an RO 440 bus drive axle.

Predictive Powertrain Control (PPC) and Eco Driver Feedback (EDF) are optionally available to support the driver with individual feedback on their personal driving style. With this combination, long maintenance intervals and its aerodynamically perfected body, the Setra S 531 DT of the TopClass 500 exploits all savings potential to the full for unparalleled economic efficiency.

The vehicle's exceptional maintenance-friendliness is also a factor here. This was an important consideration when designing the new double-decker bus. By way of example, the cooling system on the right side of the bus is now ideally accessible by means of a large maintenance door, as opposed to the previously employed two service flaps. On the opposite side of the bus, another large maintenance door affords access to the exhaust system. A new large maintenance flap on the outside of the vehicle facilitates emptying of the waste receptacle. This flap also offers improved access for any maintenance work on the sanitary installations.

Safety: Active Brake Assist 4, Sideguard Assist

The new double-decker comes as standard with long-life LED headlamps that are easy on the eyes. The emergency braking system Active Brake Assist 4 celebrated its world premiere in the bus and coach segment at its presentation. In addition to the previously available functions – maximum braking in response to stationary objects and obstacles moving ahead of the vehicle – it now also incorporates pedestrian detection with automatic braking response. Another world-first in the bus and coach segment is Sideguard Assist for the blind spot. It uses radar sensors to monitor the lane to the right of the bus along the vehicle's entire length and even beyond. When the driver turns off, the system warns of pedestrians, cyclists or stationary obstacles in the turning path. Over and above, it provides support out of town when changing lanes to the co-driver's side.

Should an accident nevertheless occur, driver and passengers benefit from the highest possible standard of passive safety. As a result, the S 531 DT voluntarily passed the pendulum impact test modelled after ECE‑R‑29. Traditionally, safety is number one on the list of priorities for Setra, a fact also underscored by the fire extinguishing system fitted as standard equipment in the new double-decker bus.