SMB136C: The Mercedes-Benz Citaro Demonstrator Unit

Main Article: Mercedes-Benz Citaro

The Mercedes-Benz Citaro is a low-floor wheelchair-accessible single-decker transit bus built by Mercedes-Benz and EvoBus GmbH. Commonly referred to as simply the “Citaro”, they are manufactured in Europe and shipped completely built-up (CBU) to Singapore.

Singapore’s two major public transport operators, SBS Transit and SMRT Buses, previously procured Mercedes-Benz Citaro buses. With the gradual implementation of the Bus Contracting Model (BCM), additional Citaro buses were procured by the Government by tapping into SBS Transit’s existing orders, and have found their way into the bus fleets of successful tenders of the various route packages.

First introduced in 2010 by SMRT Buses, the Citaro has proved popular among both public transport operators, with many more units ordered, and they are now a ubiquitous sight on Singapore roads. In 2016, there were over a thousand units on Singapore roads. And it all started with SMB136C, the first Citaro introduced to Singapore for demonstration purposes.

Technical Background:

All Citaro buses in Singapore are of the 2nd-generation 12-metre urban model with two doors. They fulfil the requirements of the Euro 5 and EEV emissions standards using BlueTec 5, the selective catalytic reduction (SCR) technology developed by Mercedes-Benz, hence requiring the use of AdBlue as a diesel additive.

The fully low floor design is attributed to its side-mounted engine which allows for smoother passenger entry and exit.

As with thousands of other units around Europe, the Citaro is completely built up by EvoBus, including its interior features (rather than a local assembly/bodywork) by factories in Europe, then shipped as a completed bus to Singapore. Local Citaros are produced in Mannheim, Germany.

A Brief History

SMRT brought in the first Citaro into Singapore for demonstration purposes. A Year 2005 face-lifted Citaro, it was registered as SMB136C, and entered service in March 2010, branded as ‘Southeast Asia’s 1st 100% Low Floor Euro V Bus”. The bus was a well-conceived continuation of SMRT’s legacy with Mercedes-Benz buses, following its long history of operating O405s and O405Gs. Positive public feedback paved the way for more Citaros in Singapore.

A Rich History:

After SMRT Buses brought in its first batch of wheelchair-accessible Mercedes-Benz OC500LEs in 2008-2009, there was a need to expand the bus fleet with more wheelchair-accessible buses to further cater to passenger demands. For Mercedes-Benz, the Citaro was the direct successor to the O405 series of buses, which SMRT operated in large numbers (along with the articulated O405G variant). The fully low-floor design, ride comfort and environmentally friendly features were promising, and SMRT decided to bring in one unit for trial purposes.

Completely built up in Europe, this unit would be very similar to other Citaros built for the European market, incorporating features such as air-conditioning for temperate climates, hopper windows for ventilation, foldable seats at the wheelchair bay, and leaf doors for the exit. Inclusive of shipping costs, import taxes and other levies such as the Additional Registration Fee (ARF), the bus was said to be acquired at a cost of over $500,000 SGD, the equivalent of the average double-decker bus and likely the most expensive rigid bus ever acquired.

Registered as SMB136C, the bus was unveiled on 9 March 2010 at a launch ceremony in SMRT’s Ang Mo Kio Depot, exactly one day after its date of registration. Along with a promotional livery, it was marketed as “Southeast Asia’s 1st 100% low-floor Euro V bus”. Fitted with Mercedes Benz’s standard 6.4-litre OM906hLA with 286hp, it delivers impressive performance while fitted to a six-speed ZF Ecomat transmission (similar to those on the OC500LE). It is also the first bus in Singapore to feature electronic destination signages (EDS) by Gorba AG. SMB136C entered revenue service exactly a week later, appearing on SMRT Service 855 on 16 March 2010.

Basic Technical Specifications
Engine Mercedes-Benz OM 906 hLA, turbocharged & inter-cooled, 6374cc
Power/torque rating of 286 hp (210 kW) @ 2200 rpm / 1120 Nm @ 1200 – 1600 rpm
Emission Standard Euro V compliant
BlueTec Selective Catalytic Reduction (SCR) emissions control technology by Daimler AG, requiring diesel exhaust fluids such as AdBlue.
Transmission ZF Ecomat II 6HP 592C gearbox, six-speed automatic
Bodywork Built in Germany by EvoBus, shipped completely built-up (CBU) to Singapore
EDS Gorba imotion Electronic Destination Signage (EDS), Orange LED matrix design
Air-conditioning Konvekta P700 roof-mounted air-conditioning pod

The comfort of the Citaro is attributed to its independent front and rear suspensions which provide a smooth and comfortable ride on a par with that of a long-distance coach. In addition, the Citaro has a quieter interior due to better body insulation. Moreover, its modular design features a fully-integrated, light-weight body, allowing for lesser vibration. These factors combine to provide passengers with a more comfortable and smoother journey on the road. Its light-weight body with reinforced longitudinal steel parts at the side walls also provides greater safety for passengers.

The weight of the Citaro is 10.98 tonnes, almost 1 tonne lighter than the OC500LE. This increases the mileage and improves fuel efficiency by about seven per cent. The bus operates on BlueTec® SCR engine technology, which converts harmful nitrous oxide emissions into mostly nitrogen and water vapour. This makes emissions from the bus cleaner and safer.

Inside, the driver’s cabin is very different from existing buses. Frequently-operated elements such as door controls are relocated to on the left of the steering wheel instead of being near to the handbrake. The handbrake is located further away from the driver and requires leaning forward to pulling it, and as such, Citaros incorporate a ‘halt brake’ to keep the bus stationary during normal operations, such as at bus stops or traffic lights, and is activated also from the dashboard. Brakes are also triggered automatically by a spring when the driver leaves his seat. In addition, the driver’s window is electrically operated, rather than manually operated in most buses.

The Citaro is also packed with many systems to enhance passenger safety and comfort, such as the Anti-lock Braking System (ABS) and Acceleration slip regulation (ASR) to prevent loss of traction under slippery road conditions. Electronic level control systems automatically adjust the vehicle height at each wheel to counter uneven load distribution inside the bus. Electronic brakeforce distribution (EBD) and Electronic Stability Control (ESC) control detects and reduces the loss of traction by varying the amount of braking pressure applied to individual wheels to maximise stopping power while maintaining vehicular control.

SMB136C uses red fabric seat covers, a default design by Mercedes-Benz. The seating layout is very much identical to its European counterparts, including seven rear-facing seats due to the axle placement. Altogether, SMB136C accommodates 37 seating and 44 standing passengers. For passengers-in-wheelchair (PIW), the bus offers one specially allocated space near the exit. This helps to minimise movement so that getting on and off the bus can be done effortlessly. The rear door is equipped with a manual wheelchair ramp, and the backrest for the PIW lot comes with a fold-down seat for two.

Air-conditioning is fully integrated into the structure of the bus, with no vents for passengers to operate. Instead, cool air comes out from holes in the ceiling of the vehicle. As with all European Citaros, the air-conditioning is designed for temperate climates, with climate control installed and hopper windows for natural ventilation. This air-conditioning was not sufficient to cope with Singapore’s tropical climate and had to be upgraded later on in its service life.

Another interesting feature is the use of a single buzzer for the stopping bell and rear door operation, rather than the normal bell and SMRT’s signature “Doors are closing”. SMRT pre-recorded announcements are not included as well. The Bus Stopping indicator is built into the bus design, with a single illuminated “STOP” when the bell is pressed. Various stickers pasted around the bus are similar to those used in European designs.

SMB136C was advertised with a ‘kneeling’ feature, which automatically lowers the bus when the doors are open, to minimise the gap between the kerb and the bus, and also aids in the boarding of wheelchair-bound passengers. This feature was disabled later and on subsequent Citaros as passengers found it to be a disruption to ride comfort.

Starting from 16 March 2010, SMB136C was under a one-year trial on various trunk and feeder routes that were ultimately successful. Passengers could give their feedback at during the trial period.

SMB136C is licensed to carry 83 passengers, including 38 seating passengers, 44 standing passengers and one passenger-in-wheelchair.

Removal of advert:

By end 2015, SMRT finally removed the promotional advertisement off SMB136C, which had been in bad shape after being stuck on for over five years. The bus appeared on revenue service in full SMRT livery for the first time in December 2015.

Shortly afterwards, the original red and black SMRT logos were replaced with new full red SMRT logos.


The trial of SMB136C was highly successful, generating much positive feedback from many commuters. Following the trial, SMRT Buses initiated the purchase of 50 more Mercedes-Benz Citaros in the first production batch, as part of its fleet renewal programme. This was spurred by LTA granting public buses an exemption from the Additional Registration Fee (ARF), making importing the Citaros significantly more affordable.

SBS Transit, having evaluated SMB136C, had another Citaro (SMB148T) modelled with its own interior specifications. It was a success, and the company proceeded to make a bulk order of 300 units. Eventually, many more units were brought in, and by 2016, there will be over a thousand units running on Singapore roads.

Gallery: (Exterior)

Gallery: (Interior)

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