Vehicle platooning: will it solve our traffic woes?

The UK Department for Transport has commissioned research to understand how vehicle platooning might benefit UK businesses, road safety, the environment and the transport network. So, what is vehicle platooning?

A vehicle platoon is a number of vehicles travelling in the same direction, nose-to-tail, close to one another (i.e. a few metres apart), at motorway speeds. The vehicles move as a group and have a lead vehicle and a number of following vehicles.

Vehicle platoons were first proposed back in 1962. Back then, we didn’t have wireless communication so most systems featured some kind of mechanical coupling to keep the vehicles the correct distance apart at speed – think of a ‘train’ for the road. As technology has improved with radar cruise control, sensors, cameras that can create 3D images, lane departure warning systems, wireless, GPS, Bluetooth and drive-by-wire throttle and steering, computers have become able to drive cars without our input. You can read about this in our article about autonomous cars here.

Platooning vehicles can communicate with one another and, as they all move simultaneously, can travel much closer together.

How can vehicle platoons benefit the UK?

In terms of this feasibility study, it’s going to focus on commercial vehicles, however, I’ve used the term car and vehicle below just to indicate anything that isn’t a motorbike (you wouldn’t have a motorbike in a vehicle platoon). A main benefit would be a reduction in operating costs for heavy haulage companies due to improved fuel consumption. Because the following vehicles travel in the lead vehicle’s slipstream, drag is reduced and this means less fuel consumed. This could mean it becomes cheaper to carry freight on the roads.

Less fuel used also means a reduction in the environmental impact of heavy haulage. The other factor in favour of the environment is that traffic flow should be smoother resulting in less congestion and this will reduce fuel economy as well as improve driving times, and reduce the need to build as many roads.

While vehicle platoons may initially only be permitted with authorised drivers and vehicles, with the drivers remaining in some control all of the time, eventually autonomous vehicles may be able to join and leave platoons at will while the ‘driver’ relaxes, sleeps, eats, reads or does work.

Computers will be in control of the platoons and they have superior reaction times to humans. This could reduce the accident rate.

What are the problems with vehicle platoons?

Unfortunately there are a huge number of problems.

• The accident rate is already reducing due to technology such as Subaru EyeSight and Volvo City Safety. These systems brake for you if they detect you are likely to have a collision. Vehicle platooning won’t have a significant impact on this already declining statistic.
• The accident rate may increase for several reasons:
  • If all cars are travelling one or two metres apart and the lead car hits an obstacle, all following cars will hit the car in front, even with perfect reaction time, as they won’t have the natural buffers that human drivers leave
  • Drivers in normal cars may try to join a platoon, but won’t have the necessary skill or technology to do so safely
  • Platoons create a long chain of vehicles that cannot be broken – other cars will not be able to move into the lane, which means that platoons can only ever travel in an overtaking lane where there are no exits. People may try manoeuvres to get across lanes which compromise their safety
  • If a pedestrian or motorcyclist is run over by the lead car, one or several of the following cars would almost certainly run over them due to the close travelling distances and long stopping distances, dramatically increasing the number of injuries
• Greater fuel economy means less tax take at the fuel pump. Governments will have to adjust budgets to account for this. This could mean that one group is unfairly penalised if tax is applied in a way that disadvantages a group that doesn’t benefit from vehicle platooning. Or, perhaps, overall fuel tax might rise.
• If other drivers aren’t aware the vehicles are travelling in a platoon they may report drivers for tailgating, or may think that it’s OK to tailgate themselves
• If drivers are used to being in a platoon then it normalises the experience of tailgating for them; they will be lulled into a false sense of security and therefore could be more likely to tailgate in their everyday driving
• Drivers may be required to have some kind of additional licence or training to drive in a platoon, but this will be extremely difficult to police.
• Each vehicle in the platoon must be able to communicate with every other vehicle in the platoon so that vehicles can join and leave. This means ad hoc networks of vehicles will be being created all the time. As no network or computer system is 100% hacker-proof, there is the potential, particularly for road freight, that it could be hijacked and stolen. High-value items such as bullion or premium cars could easily be targeted.
• Platooning is unlikely to work on single-lane roads as emergency vehicles will not be able to overtake safely, and neither will other vehicles. For this to have any chance of working on single lane roads (and even on multi-lane roads), the rear following vehicle must have awareness (autonomously) that an emergency vehicle is approaching from the rear, and be able to communicate that to the lead vehicle which then must elect the right speed and whether to pull over. As all vehicles are following the lead vehicle, pulling over might not be possible for every vehicle in the platoon right at that moment. Systems that keep cars within the lane will be useless and will have to be programmed with what a grass verge looks like (along with any other obstacles that don’t appear on the road).
• Some kind of standard communication protocol will need to be established, like with wireless communication. There’s no suggestion so far as to which organisation would be responsible for this, and it would be a mighty responsibility as any insurance company would look to 100% robustness in the instructions given from the lead car to the following cars, plus some kind of difficult encryption, which doesn’t come cheap, and therefore…
• Insurance companies are unlikely to want to shoulder any risk on technology that is unproven. Google has had an autonomous car travelling around a couple of states in the USA. It’s done over half a million miles without incident, yet it’s still not licenced to travel in all 50 states, and…
• Platooning is going to be expensive, at least at the beginning. Vehicles will need to be retrofitted with significant technology to allow them to travel so close to one another at speed. There’s no guarantee that older vehicles will be able to be efficiently modified. Newer vehicles might have a better chance if they already come with most of the required technology such as radar cruise control and GPS.
• Vehicles may need mechanical modifications to cope with reduced airflow to the radiators. Travelling in the slipstream of the vehicle in front means less cooling air is available to pass over the radiators, increasing the risk of overheating. A hot engine lasts less time, so savings in fuel may be negated by engines wearing out quicker.
• Platoons won’t work in stop-start traffic in cities, or where there are stop signs (because each vehicle must do a compulsory stop), roundabouts, or traffic lights where there’s a chance that either not all vehicles will get through during the light phasing time, or that there might not be enough space the other side of the junction for all vehicles to get through.
• If vehicles are not fairly evenly matched in acceleration and braking performance then a jerky ride may result, or the lead vehicle may pull away from a lesser-powered following vehicle on a steep incline.
• Brake fade could be an issue on long descents due to less airflow being available in the slipstream of the vehicle in front.
• Selfishness may mean that a driver doesn’t want to be the lead vehicle because the lead vehicle doesn’t receive any of the fuel economy benefits. This means that the driver may break from the platoon and slot in at the back, like geese do when flying.

The initial feasibility study into vehicle platooning should be finished by the end of the financial year, with a view to conducting a road trial in the UK sometime in 2014. There have already been road trials of a system called SARTRE (Safer Road Trains for the Environment) by Volvo in Sweden and Barcelona in 2011 and 2012 respectively, plus trials of smart highways in the USA.

With the exponential increase in computing power expected to be applied to vehicles over the next few years we will see fully autonomous cars available to the public very soon.

The study is being led by Ricardo plc in a consortium comprising them, TRL (Transport Research Laboratory), Ricardo AEA and Travel Research Ltd. Given the number of potential concerns we have outlined above, it sounds like they’ll have their work cut out.

From the problems we have outlined above vehicle platoons may only work on long motorway stretches where the platoon can travel at between 70-80mph in the fast lane where the origin and destination are the same for all the vehicles. Given the enormous logistics and potential additional dangers, it looks like fully autonomous vehicles that have the ability to travel closer, but perhaps not a couple of metres apart, are a much better proposition.

Our opinion is that continuing with research into vehicle platooning is a waste of money given the rapid rate of change and advancement in autonomous vehicles. There are already programmes underway globally to foster the development and implementation of driverless cars. Almost every manufacturer has its own version and technology for self-driving cars. The technology could be applied to heavy vehicles to improve fuel economy, reduce driver fatigue and all kinds of other benefits. This is more promising than trying to get every manufacturer to work together to make some kind of ‘road train’ with marginal benefits.