A five-year trial of platooning trucks on UK roads has found that the technology is as safe as trucks running separately and fuel savings could be as much as 4.1% - but only if roads are optimised for platooning.

The HelmUK trial was funded by National Highways and the DfT to test the use of advanced driver assistance systems allowing HGVs to safely travel close together to save fuel by slipstreaming.

The trial involved three DAF HGVs with drivers being electronically coupled to maintain a gap of 0.5 to 1 second (11.9m to 23.7 metres at 53mph). This compares with a gap of 1.4 seconds (33.6m at 53mph) for most standard adaptive cruise control systems and the 2 seconds recommended by the Highway Code.

The actual saving seen in the HelmUK trial across all three vehicles was only 0.5%, mainly because the platoon could not be safely maintained through almost half of road junctions. If the platoon could be maintained 85% of the time, fuel savings should rise to 1.8% and if it was kept together all of the time – which would require junctions to be optimised – savings could be over 4%. Test-track studies have shown potential fuel reductions of 7% for a lead vehicle and 16% for a following vehicle with much smaller gaps between vehicles.

A major concern before the trials was how car drivers would interact with the platoon, especially at junctions when cars join the motorway.

While the trial found that platooning should have a “small beneficial effect” on common, existing HGV collision types and did not increase risk to other road users or disrupt traffic flow at junctions platooned through, there is a “residual risk” for platooning systems to come into “conflict with merging vehicles at junctions”.