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Whether with turn signals, hazard warning lights or flashing blue lights, vehicles often use light signals to communicate with other road users, such as pedestrians and cyclists. As part of the EU project interACT, researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have worked together with European industry and research partners to develop new solutions that enable automated and networked vehicles to communicate safely and reliably by means of light signals. "Through our findings from interACT, we are helping to bring this forward-looking technology to the road and make interactions between networked, automated vehicles and other road users safe and understandable," says Katharina Seifert, Director of the DLR Institute of Transportation Systems in Braunschweig.

LED strip gives automated vehicles 'a voice'

Light is a good way of transmitting simple messages to other road users. Language and symbols, in contrast, can easily lead to misunderstandings. The project partners have developed a special LED light strip with this in mind. It runs beneath the windows and around the whole car, flashing several times if the automated vehicle wants to let a pedestrian cross the street. The message is "I am stopping for you."

"We have devised a completely new language in order for this kind of communication to work. We tested and verified everything meticulously beforehand – from the colours to the duration of the flash and the number of repetitions," says DLR scientist Anna Schieben, who was in charge of the project. A second small lamp attached to the front of the windscreen at rear-view mirror level supplements the light strip. It can only be seen by a single person, who therefore knows that the flash emitted by the LED light strip is meant for them. The vehicle tells the rod user, "I am signalling to you", thus preventing any misunderstandings.

Support – communicating about movements and driving style

"That said, light signals alone are not sufficient for communicating in traffic," stresses Schieben. "The automated vehicle also has to be clearly seen to adapt its driving style, for instance by slowing down to a significant extent. Only then will people be confident that the car has actually noticed them." The interACT team developed a central software module for that purpose. This adjusts the driving style of the automated car at the same time that the light signals are displayed.

Seen through a scientific lens – human–machine communication

At the beginning of the project, the researchers used cameras, radar sensors and surveys to investigate how communication generally works in road traffic. From this they derived requirements for automated vehicles and used simulations, volunteer studies and real scenario tests to develop two demonstration vehicles, including all of the necessary hardware and software components. The team primarily looked at relatively uncontrolled situations in their scenarios, such as crossings without traffic lights or car parks. In such places, road users are forced to communicate and cooperate with one another. When does the light need to come on? How close can and must the vehicle be when that happens? How easy is it to see the light? In subsequent studies with test subjects, they also learned how people reacted to communicating with the automated vehicle and determined which misunderstandings might arise, for example due to the presence of non-automated vehicles in the vicinity.

Project partners and funding

Eight industry and research partners from Germany, Italy, the UK and Greece worked together on the interACT project, which was led by the DLR Institute of Transportation Systems. The companies and institutions involved included BMW, Centro Richerche Fiat (CRF), HELLA, Institute of Communication and Computer Systems (ICCS), Bosch, the Technical University of Munich (TUM) and the University of Leeds.