How will platoons of autonomous trucks work on UK roads?
With the news that the UK is to get its first platooning trial underway next year with DAF supplying the vehicles, CM has picked out some of the highlights from the feasibility study published alongside the announcement itself.
Produced via a partnership between the Transport Research Laboratory, Ricardo and Transport and Travel Research, the 100 page-plus document lays out the groundwork that will inform the £8.1m trial and lists some of the challenges ahead and misconceptions about the technology.
The authors point out that having ratified the Geneva Convention on road traffic, similar to the 1968 Vienna Convention on road traffic, there is nevertheless a misconception about what this allows you to do on UK roads.
The authors point out that the convention is often misquoted as requiring the driver to be permanently in control of their vehicle whereas it actually requires the driver to be capable of controlling the vehicle at all times. In short, a trial of autonomous trucks or any other vehicle is unlikely to need a change in the law.
Benefits – safety, fuel economy and traffic flow
Safety - The public are uneasy and the road transport industry seems divided about the advent of autonomous trucks. However, drawing on several previous studies the authors point out that improved safety should be one of the big wins. With the horror crash on the M1 fresh in our minds, the authors point out that 90% of accidents involve driver error. Automatic control or driver assistance will reduce the magnitude of risk.
Fuel economy - Various studies come up with different ranges for fuel saving but all agree there will be benefits with more to be gained the closer the trucks are to each other. PATH, one of the studies cited puts fuel economy savings at 20% for four or more vehicles and 30% for ‘many vehicles’. While aerodynamics are important, it’s a given that those following the lead vehicle will see the largest efficiency gains.
However, the report adds that lead vehicles will benefit also as the low pressure found behind it normally will not be as low when platooning with a following vehicle nearby. This means the lead vehicle’s engine will not need to expend as much energy as it normally would to overcome the low pressure zone behind it. Hauliers are most interested in this element of the technology, according to the authors.
Congestion – Although a lot has been said about how a platoon will be accommodated on the UK’s crowded road network, a study by SARTRE has shown that controlling the following distances vehicles actually helps maintain free-running traffic (think of the slow but steady progress you make through average speed camera stretches on the motorway). When it's particularly busy automatic control reduces unnecessary acceleration and braking, leading to more efficient, safer use of the road.
Convoying and platooning are not one and the same
Convoying means the formation of groups of HGVs following a manually controlled lead vehicle using technologies to assist the driver. The drivers are required to supervise the automatic systems and be ready to take over instantly. As drivers need a view of the road the suggested convoy distance between vehicles is 12m. Platooning, where vehicles run closer together than convoying, as drivers in the line don’t need full visibility with this approach.
Platooning means the formation of groups of HGVs following a lead vehicle using technologies so that the following vehicles are controlling themselves, as close as just six metres part. A driver in the platoon is not required to actively control the vehicle. The lead vehicle is manually controlled by a driver.
But when platooning an automated system will control the distance to another truck in the platoon and even the steering (so it follows in line). As ever, the driver must be able to take control, defined here as within a few seconds.
It’s not all or nothing
Platoons would form at specific points where it’s safe and advantageous to do so. It is not an all or nothing approach. An HGV might be driven for some time manually before instigating or joining a convoy at a particular point.
The systems required to run the convoy and platoons do not yet exist
While all technically possible, the authors point out that there are no commercial systems – a bit chicken and the egg – currently on the market. OEMs believe convoying systems could be in production in one to two years’ time. Commercial platooning systems are three to five years away. However, a workaround for the trial is possible as most of the functionality and systems required for convoying already exist on HGVs (such as lane departure warning and autonomous cruise control).
Car drivers will get in the way
Forming up on the motorway means little issue in terms of infrastructure but would be an issue for other road users. For example, the platoon in the SARTRE consisted of two trucks and three cars and, with a gap size of 6m each between them, had a total length of just under 60m. The length of the convoy or platoon has particular implications at road junctions. While a 6m gap would discourage car drivers from intruding, any platoon must “be able to deal with such eventualities”.
Humans aren’t computers
A driver in a convoy must continuously monitor the status of the system and road conditions but it not required to make continuous inputs to the steering and accelerator/brake controls. While their workload is therefore lower, the authors note that sustained monitoring is not actually a task that we as humans are well adapted for. Platooning may mean drivers in the following vehicles need not make any inputs nor monitor the driving situation until such time as they are required to do so. Driver workload, if not necessarily nervousness, is therefore greatly reduced.
Based on a fleet of five 44-tonne modern artics pulling curtain-side trailers covering around 100,000km a year each, analysis suggests that to achieve financial payback for the investment in platooning technology within two years, more than 60% of journey time would need to be conducted within a vehicle platoon (based on a £1.10 per litre price for diesel).