Mar 21, 2016
- Highway Pilot Connect: fascinating further development stage of the Highway Pilot networks three autonomously driving trucks
- 40-tonners only consume 0.66l/100 km per tonne
- Trucks driving in a platoon only need half the traffic space
- Highway Pilot technology increases the safety of networked trucks
- Precise sensors and cameras ensure super-fast driving responses by the trucks
Up to seven percent lower fuel consumption and correspondingly lower CO2 emissions, plus only half of the previously required traffic space – the advantages of Highway Pilot Connect from Daimler Trucks are amazing. It stands for the electronic networking of trucks on motorways and long-distance highways, also known as platooning. Highway Pilot Connect is a further development of the Highway Pilot system. It is with this that Daimler Trucks paved the way for autonomous driving in 2014. The engineers then took the development further with the Freightliner Inspiration Truck and operational implementation based on a standard Mercedes-Benz Actros. The basis of Highway Pilot Connect is networking between vehicles and precise awareness of the surroundings.
The Highway Pilot is now approved for use on public roads throughout Germany, while Highway Pilot Connect is approved for platoon driving within the federal state of Baden-Württemberg, for the complete A81 autobahn from Lake Constance to Würzburg. Only the greater Stuttgart area is excluded from this. Daimler has received an additional approval for the A52 in the greater Düsseldorf area. Further demonstration and test drives are possible with individually granted exceptional permission.
Highway Pilot Connect: networking the Highway Pilot
Highway Pilot Connect is a perfect example of the possibilities opened up by electronic vehicle-to-vehicle (V2V) networking. Compared to the Highway Pilot, Highway Pilot Connect has additional technical functions. It underlines the development potential of the Highway Pilot using V2V communication, and also demonstrates how energetically Daimler is championing the development of autonomously driving trucks in combination with networking of its own trucks.
The vehicles are equipped with both linear and lateral guidance systems. Although they are connected to each other as a platoon for a specific route, they can each be operated independently as autonomously driving trucks. It is the fully automated lateral guidance provided by the Highway Pilot and Highway Pilot Connect that makes the great difference from other systems. It is only this that allows automated driving through active steering intervention which supports drivers and eases their workload when convoy driving over monotonous long distances.
Networking between vehicles is made possible by an onboard telematics platform. This communicates using WLAN standard IEEE 802.11p, which is used only for automotive V2V applications. While the Highway Pilot drives semi-autonomously – i.e. with automated lateral and linear control – and is not networked with other vehicles, Highway Pilot Connect communicates with other trucks and the infrastructure. It uses a combination of a radio processor and a dual multiband HF transmitter/receiver. This means that information critical to safety, e.g. recognising emergency braking when it occurs, can be transferred within 0.1 seconds and therefore very rapidly.
The system also includes a three-dimensional high digital map. This means that the truck is always fully aware of the road's course and topography. In addition the digital map and the information from multisensor fusion are used to determine the truck's own position.
The driver receives information about the status of the platoon and the traffic situation via an 8-inch monitor in the instrument panel. This displays route information as well as the vehicle's own position within the platoon as a map graphic. Each driver therefore knows the current number of platoon members and his position within the group. In addition the individual drivers are always kept aware of the traffic situation. A camera in the lead vehicle records the driving situation ahead of the truck. Its images are transferred to all the vehicles in the convoy by WLAN, and shown on each monitor.
Using a seat occupancy sensor plus seat belt buckle and hands-on detection, Highway Pilot Connect checks whether the driver is in his seat and able to intervene if necessary.
Integrated approach for efficient transport
The platooning vehicles are equipped similarly to the “Efficiency Run” 2015, with which Mercedes-Benz Trucks proved the effectiveness of the integrated approach. The objective of the integrated approach is to optimise the entire truck/transport system. Apart from the tractor unit, the focus is also on the semitrailer, tyres and fuel. Accordingly, the three standard Actros 1845 semitrailer tractors are equipped with the particularly aerodynamic 2.50 m-wide StreamSpace cab. The trucks are powered by the particularly efficient, latest-generation OM 471 engine. This heavy-duty engine with a displacement of 12.8 litres consumes up to three percent less fuel than its already fuel-efficient predecessor.
The Actros tractor units are hooked up to weight-optimised Krone Eco semitrailers. In addition to the lower kerb weight thanks to lightweight design and the use of aluminium instead of steel at the front and rear, the Eco semitrailers are aerodynamically optimised with side panelling, Wabco OptiFlow Tail (foldable rear spoilers), rounded-off underride guard, removal of stowage boxes, low-weight aluminium support legs and drip edge. Super-single tyres round off the optimisation measures for the vehicles.
40-tonners consume up to seven percent less fuel in a platoon
On the motorway the semitrailer combinations forma platoon with a distance of only 15 m apart. This small distance considerably reduces air resistance, thereby lowering fuel consumption and CO2 emissions by around five percent. On level roads this makes fuel consumption figures of around 25 l/100 km possible for a loaded semitrailer combination with a gross weight of 40 t.
This corresponds to a consumption of only 0.66 l/100 km per tonne, or CO2 emissions of 13.3 g per kilometre per tonne – well below that of any passenger car with an internal combustion engine.
Measuring drives on a level test route with three semitrailer combinations at a constant speed of 80 km/h have even shown a fuel economy advantage averaging seven percent. This advantage is at different levels depending on the position in the platoon: In a three-vehicle platoon the lead vehicle has a fuel advantage of two percent, the middle vehicle eleven percent and the rear vehicle nine percent. These differences are due to the differing aerodynamic effects on the individual vehicles.
At the same time a platoon reduces the required traffic space on motorways to a minimum. Altogether three semitrailer combinations require a length of only 80 m, instead of the current 150 m with the prescribed safety distance.
A platoon can be formed at the touch of a button
This is how a platoon is formed: The driver of a semitrailer combination uses the blue button provided to activate the Highway Pilot and to switch from manual to automated driving mode. The Highway Pilot sends out a signal: "Highway Pilot Connect available". If another truck wishes to join as a platoon, its driver presses a second light-blue button in the cockpit. His truck now automatically links up with the lead truck and reduces the distance between them to 15 m.
If required, further vehicles can connect to the platoon as it forms. The maximum length of a platoon is not limited by the range of the transmission signals, but by the number of vehicles. As a stable connection must be assured at all times, and a "concertina" effect can occur from a certain platoon length onwards owing to braking and moving off within the convoy, which would give rise to tailbacks, it is not appropriate to link more than ten vehicles.
A platoon can consist of vehicles from different operators – all they need is the same technical standard. It is even possible to derive future business models from this – perhaps having vehicles from operators with regular route services taking it in turns to join together into platoons on motorways for certain stretches of a route. The shared advantage is this: all those involved noticeably reduce their fuel consumption by driving in a platoon.
Safety distance is maintained, reactions are smooth
Linking a sequence of vehicles in a platoon is similar to sporting competitions such as team time trials in cycling or wind-sheltering runners in athletics. In these cases the contestants who follow benefit from the effort of the leader.
Unlike in sporting competition, however, the necessary safety distance is always maintained between the individual trucks. If the lead vehicle or another vehicle in the platoon brakes, all the following vehicles are also braked automatically. If the lead truck accelerates to the maximum permitted speed, all the other trucks in the platoon follow suit. There is no overtaking, the lead truck dictates the speed of all the vehicles in the platoon.
In the interests of comfort and fuel consumption, the reactions of the following vehicles in the platoon are not abrupt but smooth.
The secret behind the distance: lightning-fast reactions
A considerably shorter safety distance is adequate for trucks in a platoon: if emergency braking becomes necessary, all the following vehicles react accordingly. This very effectively prevents rear-end collisions. The secret behind the short distance is that the technology has a reaction time of just one tenth of a second. Compared to this, the perception time required before a driver reacts is 1.4 seconds.
In other words, a vehicle in a platoon travelling at 80 km/h covers only 2.2 m before braking if an incident occurs. The distance is around 30 m if the driver is driving manually. Despite the reduction in distance to 15 m, complete safety is maintained as when keeping a conventional safety distance.
To ensure the maximum braking effect from the start, Highway Pilot Connect when activated overrides the emergency braking system Active Brake Assist. If a vehicle ahead performs an emergency braking manoeuvre, all the following vehicles in the platoon also perform emergency braking because of the short distance between them. For safety reasons the familiar sequence of warnings from Active Brake Assist is overrriden. When the platoon is dissolved, Active Brake Assist is automatically reactivated.
Platooning in practice: Highway Pilot Connect in action
Daimler Trucks is already technically capable of demonstrating the diverse functions of platooning on the road and in flowing traffic today with Highway Pilot Connect. Both the formation and separation of a platoon, as well as its interaction when other road users move into and out of the platoon's traffic lane or there are braking manoeuvres, can take place safely at any time at a speed of 80 km/h. These situations are currently being tested further in real traffic conditions, e.g. on the approved public A71 autobahn.
Thanks to the 15 m distance between vehicles, the platoon visibly presents no insurmountable obstacle for other road users. Car drivers are quite familiar with such distances between trucks from situations where there is dense traffic.
If a truck driver switches on the Highway Pilot for the autonomous driving function and the additional Highway Pilot Connect function, other correspondingly equipped vehicles can link up and combine to form a platoon. To make sure that other road users recognise it as a platoon, both the tractor units and the semitrailers are equipped with rotating beacons. These are activated automatically as soon as Highway Pilot Connect is active.
If a platoon approaches another truck with Highway Pilot Connect travelling ahead, this vehicle becomes the lead vehicle and the platoon has a new formation. If there is another vehicle between the trucks during the approach, the usual safety distance is maintained automatically.
Thanks to camera surveillance of the traffic ahead, all members of the platoon react automatically to safety-related situations. If one vehicle switches on its hazard warning system, the vehicle immediately behind it automatically increases the safety distance, and during this phase the vehicles remain passively linked to each other.
Cars can cut in and pass through the platoon quite safely
If a vehicle without Highway Pilot Connect cuts in on the platoon as it is cruising along, the truck behind it immediately increases the distance. In this phase the truck remains passively linked to its lead truck until the vehicle cutting in has left the platoon again. It then moves up to the previous distance.
If the lead vehicle comes up behind a slower-moving vehicle, the speed of all the platoon members is automatically adjusted to suit. Any overtaking manoeuvres are carried out manually. When the lead vehicle activates its indicators for a lane change, this information is transmitted to the following vehicles. Their drivers are prompted to carry out a lane change as well by visual display and acoustic signals.
Highway Pilot Connect also manages complex traffic situations without problems. This is based on its unrestricted automated driving capability. If a vehicle leaves the platoon at a motorway exit, for example, and its lead vehicle brakes at the same time, the vehicle leaving is also braked automatically.
If a driver overrides Highway Pilot Connect by performing a manual braking manoeuvre, for example, the platoon is immediately dissolved and the driver is informed in the cockpit display. The V2V connection is maintained, however. In the normal case the driver wishing to leave the platoon and take a motorway exit will deactivate Highway Pilot Connect and leave the convoy, which will continue on its route.
Thanks to networking with the local infrastructure, the platoon is also able to respond flexibly to special traffic situations. If a longer distance between trucks is required owing to the maximum load capacity of a bridge, for example, the platoon will lengthen its distances. This is done manually in the first stage of the Highway Pilot Connect project. On encountering the relevant road sign, the driver of the platoon's lead vehicle presses a button to render it passive. As a result the distance between the vehicles is automatically increased from 15 m to 50 m. After passing the hindrance, the platoon reorganises itself at the touch of another button. In conjunction with traffic sign recognition, it is conceivable in the future that the platoon will automatically respond to relevant signs. This also applies to speed limit signs and other traffic information.
Highway Pilot and Highway Pilot Connect: Extremely precise sensors and cameras
The technical equipment of the Mercedes-Benz Actros with Highway Pilot Connect is fundamentally based on the Highway Pilot with its capabilities from the Mercedes-Benz Future Truck 2025, the first autonomously driving truck. A radar unit with two sensors located in the lower area of the front end scans the surroundings and the speed of the vehicle ahead. The long-range sensor has a range of 250 m and covers an 18-degree segment. The short-range sensor has a range of 70 metres and scans a 130-degree segment. The sensors operate very precisely: they can measure speed with a precision of 0.1 km/h, and distance to 20 cm. The radar unit is the basis for the proximity cruise control and emergency braking system Active Brake Assist 3, which are already available today.
A stereo camera identifies road features, objects and free spaces
The area ahead of the truck is also scanned by a stereo camera located above the dash support behind the windscreen. The range of the stereo camera is 100 metres, and it scans an area of 45 degrees horizontally and 27 degrees vertically.
The stereo camera identifies one and two-lane roads, can precisely measure gaps and registers the information from road signs.
In addition to object and distance recognition, the stereo camera recognises lane markings as a major function for autonomous lane guidance. Trucks with the Highway Pilot and Highway Pilot Connect not only have linear but also lateral guidance.
Multisensor fusion: fusion of the data from all sensors
The sensors and camera images are networked (multisensor fusion). Their data are combined in a control unit of the central computer, and provide a complete picture of the surroundings. All moving and stationary objects in the truck's vicinity are registered. For comparison: the human eye has a 150-degree angle of vision, but its focal area is merely a fraction of this. This sensor data fusion and new algorithms, i.e. instructions, assist the onboard computer when choosing a suitable driving strategy.
The sensor and camera technology is effective across the entire speed range from standstill to the maximum legally permitted truck speed of 80 km/h, and therefore covers all traffic situations. By intervening in the steering, it automatically keeps the truck safely in the centre of its lane. The Servotwin steering consists of a hydraulic steering system in combination with electro-mechanical servo assistance. This allows active lateral guidance supplementing the longitudinal guidance.
Major advantage: lateral guidance without a platoon
The great advantage of Highway Pilot Connect is this: Because of their technology, all the members of such a platoon continue to be autonomous trucks. They are able to maintain their position independently of the vehicle ahead, and thanks to their combination of linear and lateral guidance, they can make a smooth transition from platoon to autonomous driving if something happens. In this case the driver does not need to intervene. Highway Pilot Connect once again becomes the Highway Pilot.
This is conceivable in cases where several third party vehicles cut into the platoon or leave it at motorway exits, or where the platoon has to dissolve owing to the traffic situation. In these cases too, the driver does not go beyond his role as an observer and supervisor – a solution that is both comfortable and above all safe.
Only minor differences in the cockpit
The cockpit of the Actros with Highway Pilot and Highway Pilot Connect is similar to the exterior design in having no immediately obvious differences from the standard model. Noticeable on the right side of the instrument panel are two blue push-button switches for activation and deactivation of the Highway Pilot and Highway Pilot Connect. The activation status is shown to the driver by LEDs lighting up in the two buttons.
Transmission of messages is via the radio processor with multiband HF transmitter/receiver. The navigation system informs the driver of any obstacles such as roadworks.
V2V – vehicle-to-vehicle communication
The Highway Pilot and Highway Pilot Connect are perfectly complemented by V2V and V2I networking, i.e. Vehicle-to-Vehicle and Vehicle-to-Infrastructure communication. Every vehicle equipped with this in the near future will transmit continuous information to its surroundings, the CAM (Corporate Awareness Message) and DENM (Decentralised Environmental Notification Messages). The vehicle uses this to announce its presence. These are standard, industry-wide messages for networked vehicles of whatever manufacture – they can communicate with each other and with the infrastructure. The information content includes vehicle position and model, dimensions, direction of travel and speed, any acceleration and braking manoeuvres and the bend radii negotiated.
The frequency of information transfer depends on the vehicle speed and the intensity of any changes in its movement. It varies between one message per second when cruising to ten times this interval when changes are significant.
Transmission is via WLAN technology, using the standard Europe-wide G5 frequency of 5.9 gigahertz. The basis is the ITS Vehicle Station (Intelligent Transport Systems and Services) on board the vehicle. Communication between vehicles is also standardised following an agreement between a consortium of automobile manufacturers, suppliers, public organisations and research institutions.
Predictive driving – fast reactions
The range of these continuous messages is a radius of around 200 metres. The vehicles inform each other about their movements, so that they can respond to them immediately in anticipatory mode. This includes e.g. reacting to vehicles joining a motorway, or when approaching the end of a traffic tailback. Each of these messages is certified to prevent misuse. Transmission to this distance also works in unfavourable weather conditions.
If necessary the continuous reports are overlaid with DEN messages (Decentralized Environmental Notification). These give a warning of unusual events, for example emergency braking, activation of the hazard warning system or switching on fog lamps.
V2I – communication between the truck and infrastructure
V2I means that all these messages and signals are also sent to external recipients such as traffic control centres. These are then able to respond flexibly, for example by changing the speed limit or opening up additional lanes.
Messages can also be sent to the vehicles. In the future this information will be sent by intelligent traffic systems. Overhead gantries, for example, will then relay information about speed restrictions, roadworks or fog/ice warnings to passing vehicles and to traffic control centres. If the next relay station for V2I is out of direct range, the information is relayed via other vehicles in the form of a transmission chain. If there is no WLAN network, transmission is by mobile technologies such as UMTS and GPRS.
All these data inform the driver or the onboard computer about events happening outside the range of vision in good time. The driver and vehicle are therefore aware of problems in advance, before they can become a hazard.
Highway Pilot Connect: Fascinating further development stage of the Highway Pilot
With the Highway Pilot, Daimler Trucks has shown that autonomous trucks are becoming a reality. Highway Pilot Connect is one of the fascinating further development stages of this concept. This project is based on the Highway Pilot, and shows the additional potential of platooning: without compromising safety, trucks can drive in convoy on motorways at close distances. Platooning reduces fuel consumption and therefore CO2 emissions, while also reducing the increasingly congested traffic space requirement. Platooning is therefore an important added component on the road to autonomous driving, based on networking several trucks. Demonstrations on public roads have already shown that Highway Pilot Connect is not a far-off vision, but technically already feasible.