Informal communication in traffic.

  • 5. November 2014
  • Autonomous Driving
  • Photo: © Getty Images, Suzanne Lee
  • Text: Patricia Piekenbrock

Road users often communicate with one another according to unwritten rules – a challenge for autonomous vehicles.

Road traffic is controlled by general traffic regulations. Drivers use their turn signals and brake lights or flash their headlamps in order to communicate in a specific situation. Such signals are not easily recognized by an autonomous vehicle. Road users also communicate according to unwritten rules and send informal messages with gestures, glances or waves of the hand. The Villa Ladenburg project of the Daimler and Benz Foundation (Daimler und Benz Stiftung) provides a platform for scientific analysis of issues related to automated driving. Issues of social relevance – such as the use of informal means of communication in traffic – are at the fore.

When strict observation of rules could lead to disruptions, delays or dangers on the road, road users often react spontaneously and situationally in order to make themselves understood. Drivers communicate with one another, but also with pedestrians and cyclists. “People take a schematic approach in this respect. Their thoughts and actions reflect a certain pattern, which allows them to deduce how another road user will behave”, explained Professor Berthold Färber of the Human Factors Institute at the Armed Forces University in Munich, a psychologist and external expert working on the Villa Ladenburg research project. “They expect an older person to react differently from a child; and a different style of driving from a sports car driver compared with a sedan driver.” If a pedestrian is seen walking purposefully towards a crosswalk, the driver will assume that the pedestrian possibly intends to cross the road. The pedestrian’s action is anticipated on the basis of the movement pattern.

According to Färber, these informal channels of communication play a major role in the numerous daily traffic situations where action is required – particularly in the lower speed range in cities. For example, pedestrians generally make eye contact with the driver to ensure that they have been seen and can cross the road safely. A driver turning from a side street into a busy main road may also attempt to establish eye contact in order to see if he will be allowed to merge in the traffic flow. If the target person averts his eyes, the inquirer perceives that he hasn’t been seen or that the other person is not willing to enter into a negotiation. A positive sign, such as a nod or a wave, indicates willingness to cooperate.


However, this interpersonal communication is lost when drivers of conventional vehicles encounter automated vehicles. If there is no one in the driver’s seat, there can be no way of reaching an understanding. And indeed, should eye contact be made with the occupant of the robotic vehicle, who is perhaps thinking about other things at the moment, the situation could give rise to serious misunderstandings. According to Färber, one way out of this dilemma would be to clearly mark autonomous vehicles as such during the transitional phase in mixed traffic: “This could avoid annoyance and even have a positive marketing effect under certain circumstances.” On the other hand, there is also a risk of undesired intervention by third parties – when the stopping or obstruction of an autonomous vehicle becomes a fun way of passing the time.

“Right now we are looking at whether typical misunderstandings between humans and robots can be predicted”, explained Färber, “and at people’s mental reaction to the strictly regimented behaviour of automated vehicles.” Thus, the scientists working on the Daimler and Benz Foundation’s Villa Ladenburg project are taking both a psychological and a technical view of new forms of communication for an effective exchange of information. According to Färber, in future, autonomous vehicles should be able to recognize the gestures and trajectories of other road users, to interpret these and ultimately even to provide feedback by using the indicators or flashing the headlamps. A robotic vehicle will also need a clearly recognizable style of driving, which a human can immediately gage. In heavy traffic, for example, it would have to allow for a sufficiently large distance in order to allow another vehicle to merge into the traffic lane safely.


The researchers are also examining ways in which cultural or typical national differences in informal communication and expected behaviour can be applied to the response of an autonomous vehicle. While, in Germany it would be extremely difficult to cut into heavy traffic without the informal agreement of the other party, in Southern Europe there is no expectation of feedback in such situations. Typical indications of intent to merge into the flow of traffic include accelerating the car and sounding the horn. In China, on the other hand, sounding the horn is understood mainly as a greeting. Signals used in Central Europe, such as eye contact, nodding or hand signals, are only of minor importance in the US: The traffic there flows more evenly and fewer lane-change manoeuvres are undertaken.


The concept of “Shared Spaces” represents a whole school of thought around urban and traffic planning, and looks at the advantages of informal communication between different road users. The key approach: Pedestrians, cyclists, motorists and all other players in the traffic environment have equal rights and observe the conventional right-of-way rules. On the other hand, legal prohibitions and regulations become largely obsolete, thus removing the need for signs, traffic lights and curbs. The need to give consideration to others becomes the top priority, along with direct communication, for example through eye contact or gestures. The latter, in the absence of any impersonal overriding rules, inevitably become the key means of coping with uncertainty in traffic.

The “Shared Spaces” concept has been developed and propagated since the 1990s, primarily through the efforts of the Dutch traffic planning expert Hans Monderman (1945 – 2008). Monderman was convinced that his concept could both improve the quality of life in public spaces and improve road safety. “Once people look each other in the eye”, claimed Monderman, “nothing can really go wrong any more.” Many different communities have gone on to use Monderman’s concept, thus confirming his ideas – although not all projects have been equally successful.

Prominent examples of the “Shared Spaces” concept in Europe include the towns of Bohmte in Germany and Haren in the Netherlands, as part of an EU model project. Larger cities, such as Stuttgart (Germany) and London (UK), have also converted parts of their inner cities into “Shared Spaces”.

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