Safety by Design: The Structural Concept of the Next City Bus Generation

• Compact Height, Clear Length Logic: The Key Dimensions
• Modular Design Principle: One Vehicle Family, Seven Variants
• New Body-in-White and Body Concept: The Basis for Efficiency and Safety
• A Structural Element in Its Own Right: The New Sandwich Roof
• Straight Instead of Curved Side Walls: Modularity at Work
• New Rear Layout Creates Additional Flexibility
• Passive Safety: Defined Crash Zones and Crash-Protected High-Voltage Components

With the next-generation eCitaro, Daimler Buses is introducing not only a vehicle consistently designed for electric propulsion, but also a completely new vehicle structure. The body-in-white, roof and underbody have been developed from the ground up for the new generation, with the goal of simultaneously optimizing weight, safety and passenger capacity.

The new generation will initially be launched as a low-floor model range. In a second step, Daimler Buses will expand the portfolio with a low-entry (LE) variant covering both Class I vehicles (urban buses) and Class II vehicles (intercity buses).

Compact Height, Clear Length Logic: The Key Dimensions

As a low-floor city bus, the eCitaro successor has a maximum exterior height of approximately 3,220 millimeters, around 180 millimeters less than today’s eCitaro. The core low-entry model with Class II approval has a vehicle height of 3,400 millimeters. Regardless of the selected charging infrastructure, the roof-mounted air-conditioning system remains the highest point of the vehicle: neither the pantograph nor the charging rail affects the vehicle’s maximum height. The interior standing height differs deliberately between the low-floor and low-entry variants in order to optimize the conditioned interior volume and thus reduce energy consumption for heating and air conditioning. Based on a common front module and rear module, the new generation will be available in three lengths: a 10.63-meter solo bus, a 12.13-meter solo bus and an 18.13-meter articulated bus. The low-entry variant will be offered in four lengths: 10.63 meters, 12.34 meters, 13.08 meters and 14.68 meters.

Modular Design Principle: One Vehicle Family, Seven Variants

The different vehicle lengths of the new city bus generation are based on a clearly structured modular architecture. A standardized front module is combined with an identical rear module across all variants, housing, among other components, the drivetrain and most of the high-voltage equipment. Combined with center modules of varying wheelbases, this approach creates the different vehicle lengths within the model range. The modular design principle allows a variety of vehicle lengths to be offered without compromising safety, performance or operating concepts.

New Body-in-White and Body Concept: The Basis for Efficiency and Safety

The successor to the eCitaro features a newly developed body-in-white and body concept incorporating low-profile compact batteries integrated into the underbody. Through battery positioning, optimized packaging and structural adaptations, Daimler Buses has specifically reduced vehicle weight. Equipped with eight compact battery packs, the new city bus generation weighs approximately 13,050 kilograms, compared with around 13,800 kilograms for the current eCitaro with five NMC4 battery packs, representing a reduction of approximately 750 kilograms. Further optimization potential results from integrated component functions, simplified assembly and interface concepts, and targeted material savings. The advantage is clear: the lower curb weight and optimized weight distribution enable a passenger capacity on par with the diesel-powered Citaro.

A Structural Element in Its Own Right: The New Sandwich Roof

For the first time, the new city bus generation features a multi-layer sandwich roof. Unlike the previous steel roof, where the steel structure, insulation and interior ceiling were separate components, the new “integral roof” combines structural, insulating and design functions within a single component. Two aluminum outer layers, each approximately one millimeter thick, enclose a foam core around 40 millimeters thick. This core acts as insulation and helps reduce the energy required for heating and air conditioning. With an overall thickness of only around 42 millimeters, compared with approximately 70 millimeters for the steel roof, the new roof also contributes to a lower overall vehicle height. At the same time, the new roof structure reduces vehicle weight by around 100 kilograms for the 12-meter solo bus and approximately 150 kilograms for the 18-meter articulated bus.

Straight Instead of Curved Side Walls: Modularity at Work

While the current eCitaro features slightly curved side walls, the successor adopts completely straight side walls without the slight inward taper towards the roof previously used. This configuration is a deliberate engineering decision. The straight side wall allows both the new integral roof and the underbody structure to be standardized. With curved side walls, the differing vehicle heights of the low-floor and low-entry variants would have required different radii. As a result, each variant would have needed its own roof and underbody design. The straight side wall instead creates a clearly defined and efficient geometry, enabling a high level of standardization across the entire product range.

New Rear Layout Creates Additional Flexibility

The elimination of the traditional rear engine tower opens up new possibilities for rear-end packaging. Depending on the vehicle configuration, the rear section can now be designed as a fully low-floor area without a raised platform. At the same time, all safety-related requirements for the rear structure remain fully intact.

Passive Safety: Defined Crash Zones and Crash-Protected High-Voltage Components

The new generation of city buses follows an integrated passive safety concept that combines occupant protection with the crash-safe installation of high-voltage components. The placement of the key high-voltage components in the rear section of the eCitaro successor is the result of a deliberately safety-driven design approach. These components include the inverter, the high-voltage distribution box with fuses and main contactors, as well as the Charge PDU (Power Distribution Unit), which distributes charging current throughout the vehicle. The positioning of these components is based on defined crash zones within the vehicle, derived from both regulatory requirements and experience gained in the commercial vehicle sector. High-voltage components must either be located outside the crash zones or be additionally designed and protected to withstand impacts. The new generation of city buses therefore continues Daimler Buses' philosophy of impact-protected installation of battery and high-voltage components in the rear section, a concept already implemented in the current eCitaro. At the front, the proven front impact protection system is once again employed as an integral part of the overall safety concept in the new vehicle generation.