The Chair organized a brainstorming with the aim of determining the issues at stake and that should be addressed by the informal group:

The group was informed that D is willing to develop regulations for multiple trailer combinations.

The problem of air supply was raised, e.g. in the case of multiple trailer combination, on slippery road with ABS continuously operating: air capacity would be exhausted after about 20 s.

In addition, a limit should be given related to the traction capacity of the tractor. The Chair raised that no “mass & dimension” regulation could be established in the frame of the UN 58 Agreement.

MAN suggested that the preceding vehicle is responsible for providing air to the following vehicle, hence the full responsibility would not be on the sole tractor. For what regards the air supply, Volvo did not find necessary to regulate that as it is more a question of vehicle manufacturer vs. operator relationship (there is currently no safety issue with current systems).

Volvo suggested to focus on certain, to be defined, combinations in order to simplify the work in the informal group. It was proposed to base the work on the ISO 18868-2013. A debate took place about the criterion for regulating the traction capacity in the regulation: towed load, number of trailers, number of axles, other? The formula of braking system air consumption can be found in Annex 7, paragraph 2.3.3. Yet the suspension air consumption could be added to the list of parameter to be addressed.

The concern of information transmission was also raised: the tractor has the need to be informed on the status of the last trailer braking state. This would be feasible with EBS braking system. Industry could accept that EBS be mandatory for modular vehicle combination. VGB recalled that EBS only is not permitted today. CLEPA recalled that the proposed informal document GRRF-66-08 already requested that all towing trailer be equipped with EBS; only the last trailer could be permitted without EBS. Yet there is a need for communication with the last trailer. As the lack of communication currently means that there is no trailer, there would be a need for additional requirements through e.g. coupling sensors, working in conjunction with the braking signal. Relevant additional HMI would also be necessary.

Parking brake: some preliminary requirements are currently developed in S. Current requirement in UN R13 is 12% slope with unbraked trailer (UNR13, Annex 4, paragraph 2.3.2.). Some approvals exist todays for 60 tons vehicles with only one axle operated by parking brake. Yet the group wondered whether this could more be an in-use problem.

Active steering via side braking for helping stabilizing the vehicle e.g. in case of brutal lane change.