First, the trial found that having a closely-packed convoy of heavy vehicles poses a risk to merging vehicles at motorway junctions. That was judged to be such an issue that during the trial the three-vehicle platoon spent nearly as much time broken up (46.5%) as combined.
Rejoining the platoon required trailing vehicles to accelerate, which consumed fuel, and that fuel consumption ate up almost all of the fuel saving of the practice over single-vehicle adaptive cruise control systems. (A thought experiment suggests that in best-case conditions, fuel savings might increase from 2.6% to as much as about 4%, compared to 7% fuel savings found on test track configurations in other studies).
However, on the positive side, the project validated the safety of a prototype control system developed by truck OEM DAF, which may have applications in future driver assistance systems or for autonomous vehicles. That consists of four key technologies: cooperative adaptive cruise control, used to maintain vehicle distance or headway with vehicle-to-vehicle communication; brake performance estimator, which calculates braking distances based on vehicle weight; cooperative collision avoidance, which coordinates automatic emergency braking; and lane keeping assistance. The system was found to keep good control of the vehicles, be fail-safe, and the collaborative collision avoidance worked to protect the platoon (although in a very few cases it might have posed a risk to following drivers). Also found to be a success was radar detection of cars and larger vehicles cutting into the platoon. During the trial, no motorcycles were found to cut into the platoon.
The trials involved three HGVs travelling on the M5 and M6 motorways between Avonmouth and Stafford, a round trip of 218mi, with a lead vehicle carrying 22t payload, a middle vehicle with 9.2t payload and a following vehicle with no payload (this configuration allowed the shortest following distances). The trial clocked up 12,000 miles over 58 days of on-road trials. The lead driver was in control of acceleration, braking and steering; following drivers had control of steering. No roundabouts were included in the route.
The initial phases of the project involved development and validation of the DAF platooning system and development of a safety case by TRL for trials. Driver tests, simulator studies and track testing was also carried out. In phase 2, DAF UK drivers under trial management by TRL validated the route, which led to it approving the system for customer field trial use.
Looking forward, the trial has demonstrated the worth of vehicle-to-vehicle communication systems such as cooperative adaptive cruise and cooperative collision avoidance on real roads, even for vehicles that are not platooning. The authors say: “These systems offer safety benefits over existing systems. HelmUK has proven this functionality using DAF vehicles and the European ENSEMBLE project has proven this functionality across multiple manufacturers. These systems could be deployed in the near term when sufficiently developed.”
The project was sponsored by DfT and National Highways and consisted of project lead TRL and project partners Apollo Vehicle Safety, Connected Places Catapult, Costain, DAF Trucks, DHL,