Augsburger Stadtwerke has the ambitious aim of making its entire local public transport operation CO2-neutral by 2017. As far as its bus fleet is concerned, the Augsburg-based public utility has already achieved this aim as the buses serving the city have been running on environmentally friendly natural gas for many years and even on 100-percent renewable natural gas for the past year. With its order for 13 Mercedes-Benz Citaro NGT (Natural Gas Technology) buses, the company is remaining faithful to this ecofriendly drive concept but, by opting for this particular classic among urban buses, wants to take passenger comfort to an even higher level. On 11 December 2015, Tammo Voigt, Head of Local Public Transport Fleet Sales at the Mercedes-Benz Bus and Coach unit, handed over the symbolic key for the first delivered Citaro natural-gas bus featuring new engine technology to Ernst Schäfer, Head of the Bus Workshops at Augsburger Stadtwerke.
Gas drive: clean and quiet around the City
Augsburg is Germany's first city to have an almost completely CO2-neutral bus fleet in service on its roads. As part of its regular fleet-rejuvenation programme, Augsburger Stadtwerke has now opted for the innovative Mercedes-Benz Citaro NGT. The new Citaro NGT with natural-gas engine sets standards in terms of environmental friendliness and comfort. It is approved for the use of renewable natural gas to DIN 51624 without restriction and discernibly undercuts the noise level of its diesel-engined counterpart. Depending on the driving status, its noise emissions are up to 4 dB(A) lower, which corresponds to the subjectively perceived noise level almost being cut by half.
Both factors – low CO2 emissions and low noise level – predestine the new Citaro NGT specifically for service in busy inner cities and for serving residential areas or old-town districts with high numbers of tourists like Augsburg.
Equipment highlights: benchmark in terms of comfort
The equipment features of the new Citaro fleet show that Augsburger Stadtwerke is not only unconventional when it comes to its choice of drive system. What first catches the eye are the strip lights which illuminate the bottom door edges and steps. Specially designed LED elements on the outside of the bus show passengers waiting at a bus stop which door to use before the bus has even come to a halt. Green means that passengers can board through this door. Red means that there is no entry at this door. The same principle applies inside the bus. An LED strip above the door lights up green to signal that this exit is available. "These controlled colour codes for the doors are essentially designed to achieve two aims," explains bus workshop manager Ernst Schäfer. "The LED strips clearly signal to visually impaired passengers which doors are available for entry or exit. These LEDs can likewise control passenger turnover, making getting onto and off the bus a far more fluid process. Plus it is designed to prevent 'bottlenecks' in the door areas - a common occurrence on school buses or at very busy stops during peak periods." The external lighting has a further advantage: the LEDs give off so much light that they illuminate the areas around the steps, which enhances safety.
Passenger safety inside the bus is enhanced by features such as a video surveillance system based on five cameras distributed evenly throughout the interior. The driver can view the recorded images in real time or replay them on a monitor in the cockpit, plus the saved images can be analysed at the control centre afterwards.
The NGT model has two multifunction areas for wheelchairs, Zimmer frames or prams. Grab rails in brushed stainless steel and blue seats combine to convey a high-quality look and feel. The Augsburger Stadtwerke logo is discreetly flush-mounted in the backrest fabric. Glass roof hatches further brighten the already very light and spacious interior. Three 29-inch TFT monitors housed in stainless steel display the current bus route, connection options, advertising and the latest news. A powerful air conditioning system and free LTE/WiFi complete the Citaro NGT comfort package. This version of the articulated gas-powered bus has 43 seats and standing room for a further 108 passengers.
New M 936 G gas engine: textbook example of downsizing
At the heart of the new Citaro NGT is the Mercedes-Benz M 936 G natural-gas engine. With a displacement of 7.7 l, it is currently the most compact natural-gas engine in its class: weighing in at just 747 kg including the precatalyst, the engine is a textbook example of successful downsizing.
The natural-gas engine is based on the highly sophisticated OM 936 turbodiesel engine. The vertically installed six-cylinder in-line mono-fuel engine runs on compressed natural gas or biogas. It has an output of 222 kW (302 hp) at 2000 rpm while delivering a peak torque of 1200 Nm consistently from 1200 to 1600 rpm. In many instances, it undercuts the Euro VI emission limits by a considerable margin. These figures, in combination with its impressive power delivery, put the single-stage turbocharged engine on a par with its diesel-powered counterpart. In the main transmission range, performance and torque characteristics remain consistent from idle speed to around 1500 rpm. Above this, the natural-gas engine actually delivers a slight advantage in terms of power and torque. Only from an engine speed exceeding 2000 rpm is the diesel engine superior to the natural-gas engine – levels that an urban bus does not reach in real-world scenarios.
At the same time, the natural-gas engine from Mercedes-Benz raises the bar for environmental friendliness particularly high, because the CO2 emissions of a natural-gas engine are up to ten percent below those of a diesel engine. Using renewable natural gas to power the bus makes the carbon footprint even better because in that case a natural-gas bus becomes virtually CO2 neutral.
Augsburg on the move
Augsburger Stadtwerke is the region's most important local public transport company. It employs 1841 people, including around 550 bus and tram drivers. The fleet of 89 buses, all powered by natural gas, clocks up around 4 million kilometres a year. The bus route network in Augsburg itself covers 137 kilometres and has 281 bus stops with 668 stopping places. Natural-gas buses first took to the road in Augsburg as far back as 1995, and the fleet has been running entirely on renewable natural gas since 2011. Stadtwerke Augsburg received the 2012 ADAC Mobility Prize in recognition of its environmental commitment and active contribution to inner-city air pollution control. The ADAC, Germany's automobile association, has awarded its Mobility Prize for innovative transportation achievements and approaches in Bavaria every year since 2001.