Communication between cars: an aid to interaction or fuel for rage?

What if you had a device that allowed you to communicate with the driver of the car that's tailgating you?  Raphael Lamas finds out if drivers would use such a device, and if so, how they would use it.

Driving is a social task where drivers frequently need to communicate with other road users to make their intentions clear and avoid accidents. Driver interaction, which is mostly nonverbal in nature, has specific characteristics that can make it difficult to determine the precise intent of each driver involved. In the first place, the vehicle creates a spatial separation and a physical barrier between drivers. Also, the interaction usually needs to be completed in a short space of time because of the high speed of the vehicles. Finally, visual information such as facial expressions or gestures may not be easily visible, especially when driving at night.

Driver interaction could be enhanced by an electronic driver-to-driver communication device, which would allow users to exchange messages with each other. Ideally, the device would be available in all vehicles and should be designed in such a way that it does not negatively affect the main driving task.

An exploratory study was designed to investigate the effectiveness of the use of a hypothetical device on the outcome of different driving scenarios. Studies have shown variations in different countries in relation to several aspects of driver behaviour. Therefore, this study also aimed to investigate how drivers from two different countries, Brazil and the UK, would interact with others in the same scenarios either in formal or informal ways.

Driving scenarios

Scenarios are extremely helpful to explore issues with any technology before it is implemented. Six different driving scenarios were used in this study to present information and evoke opinions from participants. These scenarios cover a wide range of different forms of communication:

- The main driver is unable to overtake a very slow driver in front.
- An angry driver tailgates the main driver who is driving calmly on a single carriageway.
- Interaction between the main driver and the other driver in a friendly exchange.
- While overtaking, the main driver notices that the other driver’s vehicle has a flat tyre.
- The other driver needs to give way to the main driver who is leaving a building.
- The main driver gets stuck in the middle of a junction, blocking vehicles coming from the other direction.

A total of 24 participants, 12 from each country, participated in the study. They were recruited on the basis that they had to regularly drive at least three times a week and must have held a valid driving licence from either the UK or Brazil for at least five years.

Participants were asked questions regarding each scenario they had just read. All participants answered questions based on the same set of six scenarios, which were randomised. After all the questions regarding a scenario had been answered, participants were then presented with the next scenario and the same process started again.

Some of the questions presented to the participants were related to a communication device. It was not explained to the participants what this device would be like, leaving it open to their imagination without any further information. Participants were only asked to think of an electronic device available in the vehicle, which would allow them to exchange messages with other drivers. At the end, participants were asked their opinions on what they thought would be the interface of the device and the best way to interact with it. The study highlighted important results, which will then be helpful in designing the next studies.

Although some cultural differences between Brazilian and British drivers were found using the traditional means of communication, such as honking their horn, flashing headlights and making gestures, no significant differences were found when using the device as a means of communication. Both British and Brazilian drivers would use the hypothetical communication device in the same way and with similar message content. Issues with the device, such as the potential for abusive use were found equally in both cultures.

Participants also reported they would use the device to send messages in all the scenarios but they would avoid replying to the other driver if an aggressive message was sent. Most of them would not like to antagonise an angry driver and get involved in a road rage scenario. Participants would not like to become distracted from the main driving task by engaging in a prolonged conversation with the other driver through the device, even if it was hands-free.

Several studies mention the effect of the presence of passengers on the driver. This study found that this could also equally apply when using an electronic device to exchange messages. Drivers can feel inhibited to use the device when they have a passenger with them, especially if this passenger is a child or an older person who might not react well to an aggressive or offensive message.

Design recommendations

Based on the results of the study, it was possible to draw some initial design recommendations for a driver-to-driver communication device. Firstly, it is critical to design a suitable human-machine interface that takes into consideration the distraction of drivers. Therefore, a voice-based interface has many advantages even though it may not be appropriate for prolonged interaction.

Secondly, most participants reported that they would prefer to exchange audio messages rather than text messages. Audio messages could be transmitted either with the actual voice of the driver or with a computer-generated voice. Most participants preferred a synthesised voice, especially because of their concern with how the other driver would interpret the tone of their voice. The message with the actual voice of the driver would carry their emotions and could be aggressive in tone. Emotions could change the outcome of the interaction. An aggressive reply from the other driver could make the main driver angrier.

Thirdly, drivers could only have access to a set of pre-defined messages or be allowed to express themselves freely. Although free-content messages could cover any communication scenario, they could also lead to inappropriate use. The set of pre-defined messages should be carefully considered, as a restricted number of options might limit the use of the device with a lower acceptance by the general population. On the other hand, an increased number of options could take a longer time for drivers to decide and choose which one to use.

Fourthly, it was found that it is important that the interface of the device should identify the driver who sent the message in some way. Identification could be made, for example, by giving the make of the vehicle, model and registration plate, which may not be seen by all drivers. Another option might be to display the driver’s name or picture in a visual display. Both options could violate the driver’s privacy but at the same time an anonymous message might lead to abusive use.

Finally, drivers could share with other drivers their current state. For example, this could be anything related to their current emotional feelings or a reason for driving slowly. The interface of the device would then display the information to all drivers. This information would help drivers understand why the person is driving in a particular way, making their intentions clearer and improving their interaction.

Design issues

The results of the study also found some issues related to the device. The first issue is related to the abusive use of the device. Drivers could use the device for other purposes or in frivolous talk, which could lead to drivers being distracted by an overload of unnecessary messages. Some rules of etiquette should therefore be defined before this device is available to the general public.

The device may also not be appropriate to use in all scenarios due to the duration of interaction. In some cases, the traditional means of communication could be quicker than using the device to send a message. This is especially true if both vehicles are travelling at speed on a motorway, or if the situation in which the driver needs to interact with others can be resolved quickly, for example a driver blocking others for a very short period of time

By Raphael Lamas, PhD student at the Human Factors Research Group at the University of Nottingham

This article first appeared in issue 532 of The Ergonomist, October 2014.

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