Autonomous convoys: the future of the road?

We’ve touched on the subject of autonomous vehicle convoys a couple of times in previous articles: for example, our articles on the possibilities of 5G and on how self-driving cars can benefit the environment. Convoying is a broad topic that’s brimming with possibility, though, so it’s worth taking a more in-depth look at it. In today’s post, we’re talking about the possibilities of autonomous vehicle convoys.

What is an autonomous vehicle convoy?

In an autonomous vehicle convoy, multiple self-driving vehicles follow each other closely along the same route, with the lead vehicle setting the pace. These vehicles can connect to each other and feed each other information. Each vehicle in the convoy is aware of the position and speed of the vehicle ahead of it at all times, and can adjust its own behaviour accordingly.

Autonomous vehicles don’t have to be sent out in convoys to benefit from this. In theory, an individual autonomous vehicle could detect another autonomous vehicle on the road and communicate with it over a 5G or satellite connection. This means that the vehicles would be able to behave like a convoy for as long as they’re travelling in the same direction, then go their own ways.

Increasing road throughput with connected vehicles

No matter how fast the cars on a road are travelling, that road can only hold a certain number of cars. Even in good conditions, you should keep at least a two-second gap between yourself and the car in front, so you can react if that car stops suddenly.

This space requirement means that, in normal traffic, large amounts of space on the road aren’t being used. That doesn’t mean the space is being wasted, of course; it’s crucial to have that space between vehicles in order to reduce the risk of accidents. What if we didn’t need to leave that space in order to drive safely, though?

Imagine if roads had a lane dedicated to autonomous vehicles, similar to a bus lane. The autonomous vehicles can move in sync; each one is connected to the one in front, and the entire convoy can brake or accelerate simultaneously. There’s no need for a two-second gap, because a self-driving car doesn’t need time to think before reacting to an unexpected development. If one of the vehicles needs to brake sharply, all the vehicles behind it will receive the information that it’s braking and brake at the same time.

This would hugely increase the number of moving cars the road can hold. Think about how a traffic jam can pack a lane with cars. The theoretical autonomous vehicle lane would be able to hold that many vehicles even if they were moving quickly, rather than at a standstill. This means greater throughput, more efficient travel and fewer traffic jams.

Of course, we don’t necessarily want every inch of every road to be filled with cars, even if they’re moving smoothly and quickly. For environmental reasons, governments can’t focus exclusively on making travel by road in private vehicles more convenient; they should also invest in greener modes of transport, such as cycling and trains. However, autonomous convoys do have some environmental benefits, which we’ll go into below.

Smooth movement for energy efficiency

In a convoy of connected autonomous vehicles, the vehicles can accelerate or brake at the same rate and the same time. Except in the case of emergency braking, there’s no need for sudden changes in speed. If one vehicle speeds up, the vehicle behind can speed up smoothly to keep pace with it, rather than waiting for the distance to increase and then accelerating sharply. If one vehicle slows down, the vehicle behind will expect the change in speed and won’t need to brake suddenly, as a human driver might if taken by surprise.

This smooth driving can save fuel. Sharp acceleration and sudden braking increase fuel consumption. Vehicles in an autonomous convoy can avoid unnecessary changes in speed, with a lower cost both for the vehicles’ owners and for the environment.

Has an autonomous convoy ever actually driven on the road?

As far back as 2012, in a test organised by Volvo, a convoy of self-driving cars travelled 125 miles on a Spanish motorway; you can read the BBC News article on it here. The lead vehicle was driven by a human, but the three vehicles following it were all autonomous.

Although the lead vehicle wasn’t autonomous, the following vehicles were connected to it wirelessly. As we’ve described, they were able to react instantly to any action the lead vehicle took, such as braking or accelerating.

This test also illustrates the fact that autonomous vehicles don’t necessarily need to drive with the same gap between them as human-driven vehicles. The convoy was travelling at 52 mph on the motorway. At 50 mph in dry conditions, the AA advises leaving approximately 55 metres between your car and the car in front, so you have enough time to stop if necessary. Volvo’s autonomous convoy was able to travel safely with a gap between vehicles of just 6 metres.

Autonomous vehicles may not yet be a part of everyday life, but the benefits of autonomous convoys aren’t just theoretical. We’re looking forward to seeing those benefits in action.

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