Mercedes-Benz Future Bus: safe, ecological, comfortable - semi-automated driving with the CityPilot

  • BRT lines are ideal for autonomous driving
  • CityPilot – a highly specialised and unique technical feature
  • Semi-automated driving with the Mercedes-Benz Future Bus – how the CityPilot works in practice

Ten cameras in different systems with a wide range of purposes, long and short-range radar systems, fusion of the resulting data and reconciliation with stored values, networking with traffic light systems and an automatic braking system – these are the technical requirements of the Mercedes-Benz Future Bus with CityPilot for semi-automated driving on BRT routes. The CityPilot is another milestone reached by Mercedes-Benz on the road to autonomous driving. The CityPilot is based on the Highway Pilot of the Mercedes-Benz Actros, however it exceeds the latter's capabilities to meet the needs of its specific area of operation: new functions include traffic light recognition, pedestrian recognition, centimetric precision when halting at bus stops and the ability to drive semi-autonomously in tunnels. In this way the bus becomes one with its environment not only with its design, but also with the technology it uses to move along its line and communicate with its surroundings.

BRT lines are ideal for autonomous driving

Always the same route on a separate line or track, a clearly defined timetable, defined and identical actions at bus stops: regular service city buses on BRT lines (BRT = Bus Rapid Transit) are ideal for autonomous driving. Both in the truck and passenger car sectors, Mercedes-Benz is the leader in taking steps on the way towards autonomous driving. Transferring this comprehensive know-how to the regular city service bus sector is therefore logical.

Bus operation is however subject to certain special circumstances – this is why the technology cannot simply be adopted from other vehicle systems, but must rather be developed further in the important aspects and where necessary also supplemented regarding the specific operating conditions. This applies to typical traffic situations such as traffic lights and pedestrian recognition, vehicles ahead in the same lane, passing through tunnels, negotiating junctions controlled by traffic lights, stopping and departing from bus stops and automatic opening and closing of passenger doors.

CityPilot – a highly specialised and unique technical feature

The specific operating conditions for a city bus therefore require equally specific technical equipment for autonomous driving – the cost and effort required for monitoring the road and the surroundings is extraordinarily high. Mercedes-Benz can however fall back on extensive experience with the Future Truck. This includes features such as long-range radar with a range of up to 200 m, electrically actuated Servotwin steering and the mirrorcams instead of exterior mirrors. Also familiar is the lane-tracking camera, which is used for the Lane Keeping Assist systems in other Mercedes-Benz buses and trucks. A further lane-tracking camera is used as an additional safeguard.

There are no less than four short-range radar sensors – two in the front section and two at the front corners – to cover distances from 50 centimetres to ten metres ahead of the bus. Two stereo cameras with a range of up to 50 metres allow 3D vision and recognition of obstacles and pedestrians.

Precise positioning with centimetric accuracy

Precise positioning of the Mercedes-Benz Future Bus is ensured by the satellite supported location system GPS, the lane-tracking cameras and four cameras for global visual location. These cameras are installed at front axle level high up on the sides, monitoring the surroundings and comparing them with images pre-stored in memory. Their purpose is to ensure exact positioning, and they are guided by waypoints. They operate to an accuracy of eight centimetres and are also used in illuminated tunnels. Such cameras were first used three years ago, for the autonomous journey of a Mercedes-Benz S-Class on the Bertha-Benz Memorial Route.

Two further close-range cameras are directed vertically downwards at the front sides. These recognise the pattern of the asphalt road surface like a fingerprint, and likewise compare this continuously with previously stored images of the route. And finally there are three cameras recording the journey. They record both the movements of the bus and the actions of the driver.

In this way a complex process of sensor fusion creates a precise picture of the local environment, with the exact position of the bus in its immediate surroundings. This means that it moves along its lane with centimetric precision. More precisely than a driver could ever hope to achieve manually in day-to-day operation.

Networking technical data with the traffic light infrastructure along the route ensures early recognition of each traffic light status, thus allowing a predictive, consistent and as a result more fuel-efficient driving style than is possible by conventional means.

Semi-automated driving thanks to networking – a new dimension

The result is a new dimension in the efficiency of the bus as a means of transport, thanks to networking with its environment: the bus covers its entire route semi-automatically, without the driver having to operate the accelerator or brake, or even the passenger door controls – an enormous relief in regular service operation. Strictly speaking, the Mercedes-Benz Future Bus operates at level two of the five defined levels on the way to autonomous driving – semi-automation with lane-keeping function, longitudinal guidance, acceleration and braking by assistance systems.

Intensive tests have verified safety and practical relevance

The development engineers have intensively tested the CityPilot both in test vehicles based on the Citaro and in the Mercedes-Benz Future Bus, including numerous test journeys on selected routes in closed-off areas. The world premiere in the Netherlands, on Airport Line 300 between Amsterdam and Haarlem, was also preceded by intensive tests.

One thing is therefore certain: the Mercedes-Benz CityPilot is not science fiction, it can already become a reality tomorrow. Even today, the bus is in public operation following an exemption from the state transport authority in Stuttgart according to Section 70 of the German vehicle licensing regulations, based on an expert report by TÜV Rhineland. It is allowed to operate on public roads despite deviating from the normal technical and service specifications.

World premiere on Airport Line 300 in Amsterdam

The CityPilot will celebrate its world public premiere in the Mercedes-Benz Future Bus technology platform, on Airport Line 300 in the Netherlands. This links the Dutch metropolis of Amsterdam with Amsterdam's Schiphol airport and the town of Haarlem. The route has a total length of 37.8 km, making it Western Europe's longest BRT line.

For the world premiere of the CityPilot, Mercedes-Benz is using the 19 km stretch from Amsterdam-Schiphol airport to Haarlem. This has eleven stops, with a driving time of around 30 minutes. Depending on the time of day, the cycle time on this line is six to ten minutes. On average, Airport Line 300 is used by over 125 000 passengers each day, and it is operated by the Dutch transport company Connexxion.

The route profile of Airport Line 300 is demanding: the bends are sometimes very tight, and the oncoming traffic lane is not physically separated. The route also has 22 traffic lights, three tunnels and includes high speeds of up to 70 km/h. The bus stops are raised, allowing passengers to enter the buses conveniently at ground level.

Semi-automated driving with the Mercedes-Benz Future Bus – how the CityPilot works in practice

At the first bus stop on the BRT line, the driver presses a button to switch to semi-automated mode. He/she can then release the steering wheel and pedals – the bus now moves of its own accord. It moves off automatically and accelerates to a speed of up to 70 km/h. It remains precisely in the middle of its 3.1 m wide lane, with a deviation to the left or right of at most 20 cm even at maximum speed – this is far less than a driver can manage manually for a longer period. In illuminated tunnels, even with no GPS signal, the bus safely takes its guidance from its surroundings via global, visual location cameras.

When the bus approaches a bus stop, it stops fully automatically if required. At this slower speed it moves along its prescribed line to an accuracy of two centimetres, thanks to its high-precision systems. When stopping, the bus with CityPilot maintains a very small distance of only five centimetres from the kerb. This allows convenient entry and exit, even for passengers with restricted mobility or parents with pushchairs. The doors open and close automatically at bus stops, then the bus moves off again.

Fuel-savings and a smoothly flowing driving style thanks to networking

Traffic lights en route are no obstacle to the bus with CityPilot, as it knows the traffic lights on its line. Being networked with the traffic light, the bus can influence its status and obtain 'green lights' all the way. If the wireless connection to the traffic light is interrupted, the bus uses visual recognition.

Conversely, the traffic light communicates with the bus and tells it when it is about to change. The bus then automatically adjusts its speed to the situation. The result is a highly efficient and smooth driving style. It noticeably reduces fuel consumption and therefore CO2 emissions, saves wear and tear and is also very passenger-friendly by virtue of the smooth ride.

Automatic braking when encountering obstacles and pedestrians on the road

Thanks to its radar and camera technology, the Mercedes-Benz Future Bus with CityPilot is able to recognise obstacles and pedestrians. It can identify pedestrians crossing its lane, for example. In such a case, the bus automatically initiates braking action. Additional function: at the end of a stop it does not accelerate away from the bus stop if pedestrians are crossing its path.

There is no automatic emergency braking function, out of consideration for standing passengers and those seated without a seat belt. If necessary, the driver can however take control of the vehicle at any time and take emergency braking action. The driver anyway has full responsibility at all times.

From the track-guided bus and the O-Bahn Busway to the Mercedes-Benz Future Bus

Mercedes-Benz has been a pioneer in autonomous driving in sophisticated city bus and BRT systems for decades. One of the precursors to the networked electronic systems of today's CityPilot was the track-guided bus from Mercedes-Benz. Presented in 1979, it has operated in the city of Essen since 1980. In this city bus with mechanical track guidance, side-mounted guide rollers on the wheels run along guide rails – the driver can release the steering wheel when on the move. In subsequent years the network in Essen was expanded, with track-guided buses even sharing tracks in tunnels with trams in some instances. A further track-guided bus line was operational in Mannheim from 1992 to 2005.

From 1979, at its plant site in Rastatt, Mercedes-Benz operated electrified track-guided bus routes for buses with both mechanical and electronic track guidance using a guide cable recessed into the road surface. The route included a bridge and a tunnel, as well as a fast stretch for speeds of up to 100 km/h. There was also a one-off vehicle in operation: a double articulated bus with a length of 24 metres in two-way operation.

Another great pioneering achievement by Mercedes-Benz is the so-called O-Bahn Busway in Australia. It links the city of Adelaide with suburbs. Initially set up as a test route in the early 1980s, it began to carry passengers in 1988. In peak periods the buses operated with cycle times of just under one minute and reached speeds of up to 100 km/h. The O-Bahn in Adelaide is still in operation today, and is even being expanded.

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