What is this article about?

The focus of this article is on Human Machine Interface (HMI) as main communication tool between any vehicle and the human driver. HMI includes all kinds of displays, visual and auditory, all vehicle controls that provide the communication and feedback between vehicle and driver. HMI is from even greater importance in fully automatic cars, providing mutual understanding and trust. In automated vehicles, HMI has to inform and support the human about its capabilities.

In this article, goals of HMI will be established, based on “ten challenges”, of Klein et al. (2004), which are based on the four principles of proper human-agent activity, The four principles are an agreement that actors will work together, actors must be mutually predictable in their actions, actions must be mutually directable and a common ground has to be maintained. A proposal for fully automated vehicle HMI-system will be designed in course of this article.

What should be the goals of HMI for automated vehicles (AV)?

• Provide understanding of AV capabilities and status
• Encourage correct calibration of trust
• Stimulate appropriate level of attention and intervention
• Minimise automation surprise
• Provide comfort to human user
• Be usable

In the following paragraphs, each aspect its importance for HMI is evaluated.

Provide understanding of AV capabilities and status

It is crucial for the user of an vehicle to understand which function are being provided. In an AV, users only have to understand journey-related requirements. However, a user might also want to know if the AV controls aspects a driver would usually control, such as lane keeping, ACC and overtaking another vehicle. Without indication and comprehension of different task and abilities of the AV, the user can easily be confused, which might result in mode errors, such as accidents.

In order to avoid that, a visual interface usually shows whether or not a function is activated, for example showing with colored lines whether or not the lane is properly detected. A head up display can be used to decrease the eyes-off-road time.

Encourage correct calibration of trust

Trust in a vehicle is crucial for the user to buy it. Maintaining trust is crucial, since it is difficult to regain once its lost. Studies have shown that users of AV tend to pay less attention to the road, despite the possibility that the system might fail.

Calibration of trust indicates to provide the user with the accurate knowledge about the system’s capabilities. Hereby, trust is not a unidimensional concept, but can be more seen as a fluid concept and level of trust in AV depend on the driving situation the user is in at the moment, but also to the users characteristics and experience with AV.

For a correct calibration of trust, HMI should guide the driver in actual driving conditions and under the setting used in this moment.

Stimulate appropriate level of attention and intervention

An appropriate level of attention and intervention is required to ensure safety. If a AV requires some level of control from human driver, more attention is given, which allows a safe intervention when needed. Since the system might fail, it is always required to be attentive as a user of an AV.

Eventhough it seems reasonable to be attentive in an AV, this is not always the case. The more trustworthy a systems seems, the less attention is being paid to. If the AV can keep the vehicle in the lane, why would the user see any necessity to keep their hands on the wheel?

In order to provide and maintain an appropriate level of attention and intervention, is to inform the users that if the system is known to have limitations and that the user should monitor the outer world. This also includes having the foot on the pedal and hands on the wheel, especially while driving through curves. In case systems are already known to be unsafe in certain situations, the system should also be capable of detected those situations and to inform the user

Minimise automation surprises

Automation surprise describes when the driver notices that the systems actions are inconsistent with their expectation. This can lead to absence of expected action, where the system does not perform the expected action, or to the presence of unexpected action, where the systems perform an action that does not correspond with what was expected. This might lead to danger, since the user is not aware of the abilities and capabilities of their system.

The goal of HMI is it to provide the user with observability, predictability, directability and timeliness. Observability includes the ability of the driver to understand the system status, because signals has been provided by the system through the HMI. Predictability indicates that action should be observable enough for drivers to plan their actions accordingly. HMI should predict whether or not it can or should be interfered in that situation. Further, HMI should accept, use and interpret user input to influence and be influenced to the best joint performance (Directability). Next, any unexpected situation should be signaled early enough (Timeliness).

Provide comfort to human user

Physical comfort

A main concern regarding physical (dis)comfort is motion sickness of user, due to incongruence between what users are doing and what they feel. It can be avoided by adjusting the behavior of the AV and by locating HMI in a good positions, or by adding additional displays.

Psychological comfort

This aspect related to state of well-being and minimization of stress. It is enhanced by making the driver feel at ease and by having trust and confidence in the system, which in case in increased by more often use of AV.

Usability

Usability refers to effectiveness, efficiency and satisfaction of a system. In case of AV, the usability depends on the user, the system and the current given situation. HMI can support usability by not differ too much from what the user is used to already and be more consistent to what already exist.

What does all of that mean for the implications for HMI design?

HMI is an important factor for increasing safety and comfortability in a joint cognitive system between driver and AV, to reach the best possible performance. It is important to understand how the described aspects are related to each other, and should be implemented in design of HMI.

Provide required understanding of the AV capabilities and status (minimize mode errors)

The HMI display should provide the user with an overview and understanding of what the AV is doing.

Engender correct calibration of trust

HMI should include and support observability, predictability, directablility and timeliness.

Stimulate appropriate level of attention and intervention

 HMI should make sure that driver is paying attention, and the level of attention, is fitting with the level of automation of the vehicle.

Minimise automation surprises

HMI should communicate any situation where the system is not working reliable anymore immediately.

Provide comfort to human user

The HMI display(s) should be located in a position to minimize additional head movement for the driver.

Usability

HMI should be designed in standardized ways, include for example the same symbols for automated driving, for lane keeping, for potential failure of the system.

How can the information of this article be concluded?

Even within the use of AV, it is important for users to understand the capabilities and possible inabilities of their AV. HMI is used to describe and support user in understanding of their vehicle and should increase a joint communication between AV and user.