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Author: Tony Hirst

Robot cars, part 2: Convoys of the near future

Updated Tuesday, 28th May 2013
In part two of this two-part series of articles, we look at cars that can drive themselves on public roads.

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In the second part of our special series on "A Route 66 of the Future" with the BBC World Service Click radio programme, presenter Gareth Mitchell started getting to grips with Driverless Cars. We've already seen how a new breed of road-mounted sensors and cats-eyes might hint at a future in which the roadways themselves play a more active role in the managament of the traffic that flows over them (Lighting up the roads of the future) but what if the cars take control of themselves? Not content with just letting a car park itself, as we learned about in Parking the future for now, Gareth discovered how our cars may also be drive themselves on the public roads.


Starting in 2009, the European Commission funded a three-year project in association with Volvo to explore the use of "road trains". SARTRE (Safe Road Trains for the Environment) envisioned a road train, or convoy, consisting of a lead vehicle to which a number of additional vehicles were effectivley wirelessly tethered. As described in Click, the lead vehicle drops a series of "data breadcrumbs" that provide the following vehicles with information about speed and direction being taken by the lead vehicle at each point. The lead vehicle sets the pace, with the following vehicles autonomously "accelerating, braking and turning in exactly the same way as the leader" (press release).


As well as operating on a test track, the road train idea was also trialled on public roads, In one trial, on a motorway outside Barcelona, the convoy reportedly reached speeds of 85 kilometres an hour with a six metre gap between each vehicle.


The road train idea builds on the notion of a set of follower vehicles partially slaving themselves to a lead vehicle, extending the notion of adaptive cruise control to something more akin to a game of follow my leader! This sort of approach requires communication between the lead vehicle and the following vehicles, with the following vehicles ceding a certain amount of control to the lead vehicle, or at least, accepting recommendations from it as you might listen to a talkative driving instructor. The follower vehicles then determine their behaviour using a blend of control signals made up from their own adaptive cruise control signals, as well as information provided by the lead vehicle about the actions it was currently taking or even about to take.

Personal rapid transit

Road trains provide an elegant solution to organising convoys of vehicles travelling along freeways or motorways, but are less useful in the chaos of city centre driving. But what if we could simplify the road network to only accommodate autonomous vehicles? As Gareth discovered, the pod-based personal rapid transit system that connects the business users car park with Heathrow airport's Terminal 5 achieves just that.

Using a set of dedicated roadways, the driverless, electrically powered pods take up to four passengers to their unique destination at the click of a button. While there is a human control room monitoring the system, the routing and operation of the pods is all handled autonomously.


What the pods show is how by simplifying the environment, we limit the sorts of decisions that the autonomous pods need to make in order to operate safely.

Coping with traffic

While free flowing traffic on a motorway is generally smooth flowing, aside from the relatively rare requirement of an emergency stop or swerve manouever, the stop-start nature of a traffic jam presents rather more of a challenge: cars are continuously accelerating or decelerating, at least when they aren't stuck motionless for short, arbitrary periods of time waiting for the car ahead to move. This sort of environment provides less than ideal conditions for road convoy style operation, but trials by car manufacturer Audi (among others) in the US State of Nevada are exploring how advanced forms of adaptive cruise control can provide driver support in traffic jam conditions.

While not designed as a fully autonomous system capable of taking you from door-to-door on your daily commute, "traffic jam assist" systems demonstrate how the idea of cruise control systems for cars are evolving to cope with an increasingly rich number of traffic scenarios and ever more complex traffic conditions.

Putting the pieces together

From active roadways, to self-parking cars, road trains to autonomous personal pods, one significant question remains, the question of integration. While each of the piecemeal autonomous driving operations that we have seen are no doubt impressive, from parking and driving in convoy, to coping with traffic jams or making the most of dynamic GPS route planning, we still don't know whether we can find a way of putting all these pieces together in order to create a road traffic system that supports a rich blend of autonomous and human drivers, driving safely, and efficiently, with due care and consideration for other road users, whoever, or whatever, they may be.

If you would like to listen to the second episode in the OU/BBC coproduced series of Click on "A Route 66 of the Future", you can find it here: Driverless Cars.

If you would like to learn more about robotics, you may consider studying the first-level course Technologies in practice from The Open University.


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