# Distraction Potential of Vehicle-Based On-Road Projection
## 2 Study Design
### Environment  
The study takes place in road traffic in order to determine the distraction potential of the on-road projection as realistically as possible.  
In order to achieve sustained visibility of the projection in moving traffic, both the projection vehicle and the subject vehicle drive in the same direction. This way, we create a critical situation that might lead to long distraction times. This requires a multi-lane road outside of town to avoid disturbing ambient light sources. The visibility duration depends on the differential velocity. The subject is overtaken by the projection vehicle, as this is an easier driving task for the subject than overtaking by themselves (Figure 2). Subjects can more easily turn the attention away from their own lane and perceive the projection. With this scenario we minimize the potential risk for other road users.  
Figure 1: Ishikawa diagram on main factors influencing subject studies in the traffic area.  
The study is carried out on a German motorway (right-hand traffic) in a section of the A2 between B6/A2 Garbsen slip road (point S in Figure 3) and Lauenau exit (point T1). This motorway section has three lanes in each direction and a traffic guiding system that allows a maximum speed of 120 km/h from starting point S over point T1 to point 5. In case of extraordinary incidents such as traffic jams or accidents, the speed limit is reduced. Points 1, 3, 4 and 6 are service areas. Points 2 and 5 are motorway exits where a quick turning maneuver is possible. In this way, the test track offers six places where the projection vehicle can depart after an invented overtaking maneuver in order to get behind the test vehicle without being seen. For each test drive, a randomly generated sequence of symbol projections (2\(\times\) off, 2\(\times\) static and 2\(\times\) dynamic) is determined. The test drive ends at point 6, as shown in Figure 3, and the interview is conducted with the test person. Results are presented in Section 3.  
This is followed by the second part of the test drive, in which the situation is resolved, and the test person learns about the projection vehicle. The study is continued with four more overtaking maneuvers (orange points in Figure 3), in which the test person is overtaken alternately with static and dynamic projection to compare both projection types with each other. To ensure that the projection is recognized, the subject is informed about each overtaking maneuver. After the ride, another short interview takes place in which the test person evaluates the distraction of the static and dynamic projection.  
Figure 3: Driving route from the study for the test drive, map data from [64].  
Figure 2: Symbol projection for overtaken vehicles.  
The road surface in the test section offers various types of asphalt. To ensure sufficient visibility of the projection, test drives are not carried out in adverse weather conditions such as rain, snow and fog, or when the road surface is wet. The earliest start time for the study is the beginning of nautical twilight (the sun is at least 6\({}^{\circ}\) below the horizon). With a clear sky and full moon, a maximum ambient illuminance of about 0.3 lx occurs. This way, the projection appears clearly visible to the driver of the projection vehicle. This choice of test scenario ensures that the test person can see the light projection reproducibly.  
For the scheduled test, other non-involved vehicles are advantageous so that the projection vehicle does not receive the sole attention of the subject. If the test person is being overtaken by many passive vehicles, gathered information can later be used as a reference value for the gaze time. However, the traffic density should remain low so that all scheduled overtaking maneuvers can be performed. In order to avoid traffic jams, the tests take place outside of rush hours. An increased traffic volume during the holiday season, due to special transports or police operations cannot be avoided.