Platooning ahead

SartrePlatooning may be the new way of travelling on motorways in as little as ten years time with the SARTRE project announcing its first successful demonstration. Anthony Smith reports

Just under half way through its three year programme of work, the European collaborative research project SARTRE – which stands for Safe Road Trains for the Environment – aims to develop and demonstrate road train technologies that will enable improvements in traffic flow and faster journey times, offering greater comfort to drivers, reducing accidents and improving fuel consumption, hence lowering CO2 emissions.

In landmark tests carried out in late December 2010 at the Volvo Proving Ground close to Gothenburg in Sweden, the SARTRE team for the first time successfully demonstrated its platooning technology based on a single lead and following vehicle.

Unique approach
The approach being taken by the SARTRE consortium is to develop a comprehensive platooning system contained entirely within the participating vehicles and without the requirement for any external road-side infrastructure. This is a fundamentally different approach from the many previous attempts at developing road train technologies going back over many decades; these past approaches have relied upon road-side modules for communication, location and control of platooned vehicles.

“The SARTRE project brings together a unique mix of technologies, skills and expertise from European industry and academia, with the aim of encouraging the development of safe and environmentally effective platooning,” explains Tom Robinson, SARTRE project coordinator, of Ricardo UK Ltd. “By developing and implementing the technology at a vehicle level, SARTRE aims to realise the potentially very significant safety and environmental benefits of road trains without the need to invest in expensive changes to road infrastructure.”

With road space increasingly at a premium on the crowded highways of Europe, and with public sector spending already being squeezed across member states, a system such as this, which would enable platoons to be operated safely and effectively without the need for infrastructural investment could be extremely attractive to highways authorities as we well as drivers.

If successful, the benefits from SARTRE are expected to be significant. The estimated fuel consumption saving for high-speed highway operation of road trains is in the region of 20 per cent depending on vehicle spacing and geometry. Safety benefits would arise from the reduction in accidents caused by driver action and driver fatigue, and the effective utilisation of existing road capacity would also be increased – offering a potential reduction in journey times. For users of the technology the practical attractions of a smoother, more predicable and lower-cost journey and the opportunity of additional free time will be considerable.

In the first year of the programme, SARTRE focused upon the concept development, which has seen the seven-partner consortium investigate the basic principles of a feasible platooning system. Issues investigated have included usage cases, human factors and behaviours associated with platooning, core system parameters, and specification of prototype architecture and modes of application.

Trained driver
The concept of platooning, as envisaged by the SARTRE project, involves a convoy of vehicles where a trained professional driver in a lead vehicle guides a line of other vehicles. The system is designed to be able to accommodate a range of different vehicle types including cars, trucks and long-distance coaches, and is intended to be able to operate within a mixed traffic environment alongside conventional vehicles.

Drivers of SARTRE-equipped vehicles would be alerted via a human machine interface (HMI) to the presence and destination of nearby platoons and  would be able to request access. Once control has been handed over to the platoon, the joining vehicle would be driven autonomously under the supervision and control of the lead vehicle driver. Each car or truck within the platoon continuously and automatically measures distance, speed and direction and adjusts to the vehicle in front. All vehicles are totally independent and can leave the procession at any time by resuming control via their own HMI. But, once in the platoon, drivers can relax and do other things while the platoon proceeds towards its long-haul destination.

The SARTRE system under development involves the use of cameras and radar systems for relative position sensing, GPS for absolute positioning, and automotive standard 802.11p Wi-Fi modules for inter-vehicle communications.

Tangible benefits
This form of platooning has the potential to deliver very tangible benefits to the participating drivers. Apart from the obvious advantage of freeing time for other activities through the automation of the driving process, the much shorter gap between vehicles would have benefits in terms of fuel savings thanks to reduced aerodynamic drag. In addition to making better use of the available road space, congestion would also be reduced through the avoidance of ‘ghost’ traffic jams where driver reaction time delays cause a ripple effect upon traffic flow. This is possible because the platoon control system is able to react much faster than human drivers would be able to; something that also potentially enhances safety for participating vehicles.

Before moving to vehicle tests in month 13, the SARTRE project team carried out extensive simulator-based work so that human factors in the implementation of road train technology could be thoroughly investigated. A sample group of men and women of varying ages and driving experience were tested using a simulator providing a 120-degree forward field of view via two LCD screens through which a total length of 18 km of virtual motorway could be driven. The simulator incorporated a steering wheel with force feedback, realistic manual/automatic transmission controls and a haptic seat installation; the combination provided a highly realistic virtual driving environment.

This simulator-based work has enabled the team to assess in detail the response of drivers both while participating in road trains and while driving independently in an environment in which road trains are operating. Key findings from the human factors study included assessments of the acceptable distance between vehicles and the acceptable length of a platoon (by both platoon and other drivers). In this respect it appeared that the level of acceptable platoon length was in excess of the prototype system under development, with those taking part in the study considering platoons of up to fifteen cars to be acceptable, whereas the SARTRE project is developing a prototype platoon of no more than five.

In parallel with the simulator-based work, other members of the team spent much of the first year and a half of the project working on the development and testing of the on-board systems for the first SARTRE equipped vehicles. In addition to the optical and radar sensors incorporated in both lead and following vehicles, the necessary communications and control systems architecture needed to be defined, developed and tested. To prepare for the first multi-vehicle tests, a Volvo-owned truck was equipped as a platoon lead vehicle, with an S60 sedan fitted as a participating vehicle to be driven autonomously as a following vehicle.

Having defined the overall architecture and technical specification of the system and developed the various on-board modules, the first live vehicle tests carried out in late December 2010 provided the first opportunity for testing outside the environment of the simulator.

“We were very pleased to see that the various systems work so well together already the first time,” said Eric Coelingh, engineering specialist at Volvo Cars. “After all, the systems come from seven SARTRE member companies in four countries.”

The challenge of these first tests of the platooning system was further compounded by the severe weather facing much of northern Europe at this time, with sub-zero temperatures and snow coverage. “The winter weather provided some extra testing of cameras and communication equipment,” observed Coelingh.

“We focused these first tests on the control and sensor system, and we also spent some time evaluating the first iteration of the HMI,” added Tom Robinson of Ricardo. “Issues such as longitudinal and lateral string stability have been assessed. The two-vehicle platoon was driven at up to 40 km/h with a gap size of 10 m. Both ‘join’ and ‘leave’ manoeuvres were also tested. The initial programme of testing was very successful and we gathered sufficient information to enable further development of the SARTRE system to continue.”

Technology development
With the first live vehicle tests already completed, SARTRE technology development is now well underway. Based on the work carried out to date, the project’s participants – which in addition to Ricardo include Applus+Idiada and Tecnalia of Spain, Institut für Kraftfahrzeuge Aachen (IKA) of Germany, and Volvo Car Corporation, Volvo Technology and SP Technical Research Institute, of Sweden – believe that it is sufficiently mature to be able to go into production within just a few years time.

However, what may take considerably longer is public acceptance and legislative requirements. Regarding the former, the project team is already building up a considerable knowledge base of experience built up firstly on the simulator and now on live vehicle testing. From this work the team believes that, given commercial availability of the system and appropriate lead driver and user training, these hurdles may well be overcome much in the same way that public acceptance of fly-by-wire commercial aircraft or autonomous guided vehicles is these days taken for granted. Yet, of the two, legislation is perhaps a slightly greater obstacle as compliance with existing regulations such as the Vienna convention and the requirement for new regulations specifically relating to platoons might well be required at member state level across the entire EU.

Next steps
Following these successful first tests, the next steps for the SARTRE project team are to develop and prove the system operation working at higher speeds, and with shorter gaps. Later in 2011 they expect also to start extending testing of multiple following vehicles, and also alternative ‘join’ and ‘leave’ manoeuvres. This will include, for example, the ability for vehicles to enter and leave the platoon from the side with the appropriate inter-vehicle gaps being opened up and closed automatically as necessary to enable the manoeuvre to take place.

“The first following-vehicle tests were a major milestone for what is a very important European research programme,” said Tom Robinson. “Platooning offers drivers the opportunity to utilise their time more effectively while at the same time helping society and industry to address safety, environment and congestion challenges. With the combined skills of its participating companies, SARTRE is making tangible progress towards the realisation of safe and effective road train technology.”

As development is completed in the early part of 2012, the consortium expects to be able to demonstrate a fully functioning implementation of SARTRE to stakeholders including the automotive industry, highways authorities, European government agencies, and the public.

The SARTRE project is led by Ricardo and part-funded by the European Commission under the Framework 7 programme.

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