## 4 Discussion
### Recommendations for Future On-Board Operator Workspace Design
#### 4.2.3 General Guidelines for On-Board Operator Workspace and HMI Design  
In addition to these lab-specific recommendations for on-board operator HMI design, general guidelines for workspace and HMI design are subsequently provided. Regarding the utilization of _cameras_ to provide the on-board operator with a view of the surroundings,the integration of high-quality camera perspectives is essential. This explicitly includes rear-view cameras. A helpful video stream allows operators to anticipate distances and detect small objects. It should be ensured that the camera's view remains unobstructed even when doors or windows are opened. Unhindered visibility reduces blind spots and ensures that operators have a clear view of their surroundings at all times. When it comes to _screens_, it might be helpful if the position of the primary screen with critical information is directly in front of the operator. This enables operators to perceive important information without taking their eyes off the road. Precise and responsive touch displays are critical for user interaction. Screens should be strategically positioned to provide a comprehensive overview of relevant information. They should be mounted securely to keep operators and passengers safe. Also, there is a need for a navigation display and a display that shows the shuttle's route and destination prominently, helping operators navigate effectively. Showing the driving path as a line on the display may assist operators during manual driving. When a new path has to be specified by the operator, the display line could help the operator to set the shuttle's new path accurately. Furthermore, it could be helpful to keep screens, controls, and buttons easily reachable from the operator's position. When errors occur, displaying detailed error information is imperative in order to assist operators in resolving issues efficiently, reducing downtime. This information can help operators to resolve issues through the HMI seamlessly without requiring a hard reset of the entire system, which would prolong downtime. Output channels do not have to be limited to the visual modality. A _multimodal_ approach may bring about crucial advantages. The implementation of auditory signals may be useful for notifying operators of new tasks or critical events that require their attention. The use of visual cues, such as illumination rings around buttons, can clearly indicate when a system is active. This may help operators to stay informed about the status of the vehicle functions. In order to make sure operators are fully aware of the vehicle's operating mode, it may be helpful to clearly indicate whether the vehicle automation is active or not. Color-coded output can help operators quickly identify and prioritize information and separation in the application. It might be necessary to provide output in an additional manner in case of color blindness or other vision impairments. Regarding _input_ components, illuminating buttons and controls can help operators identify and operate them safely and unambiguously. Furthermore, buttons with tactile textures or surfaces are useful to prevent fingers from slipping during use. The position of takeover buttons is particularly useful close to the steering unit, e.g., the joystick, to allow operators to swiftly take over control when needed. Moreover, the _HMI_ needs to be designed in a user-centered manner in order to ensure user-friendliness. There are several aspects that should be avoided in order to ensure the HMI of the on-board operator's workspace contributes to safe, effective, and efficient shuttle operations. In order to ascertain this, the following principles should be adhered to (see also [11; 38]):  
* Do not overuse touch buttons and balance them with regular physical buttons. * Only use buttons that contain feedback mechanisms to confirm to operators that their input has been noted. * Make sure buttons have a distinct appearance and may not be activated by mistake.