In the Netherlands, roads are classified into three categories: access roads, distributor roads, and through roads, each with distinct functions and design criteria. Nonetheless, within built-up areas, some roads have characteristics of both access and distributor roads, leading to inadequate separation of various traffic flows while having a speed limit of 50 km/h resulting in a heightened risk of accidents. These are so-called 'grey roads'. To improve road safety on grey roads, recent adjustments have been made to the design requirements. Whereas the standard speed limit on distributor roads was previously 50 km/h, it is now 30 km/h unless 50 km/h can be safely implemented. The requirements for when a road is safe enough for a 50 km/h speed limit have been tightened. Nevertheless, a combination of parallel parking and a speed limit of 50 km/h are still permitted in these tightened design requirements. Literature indicates that roads with parallel parked vehicles have an increased risk of accidents and that higher speeds increase the impact of an accident.

Due to the recent implementation of these design requirement adjustments, there is insufficient data on road accidents to determine whether road safety would improve by lowering the speed limit to 30 km/h on roads with parallel parking. Therefore, a surrogate safety measure was necessary. In this research, situational workload was chosen as the surrogate safety measure. This thesis investigated the following research question: "What is the effect of parallel parking in combination with speed reduction from 50 km/h to 30 km/h on the driver's situational workload, the feeling of safety and credibility of the speed?".

Situational workload was derived from the concept of 'mental workload,' which refers to the dynamic relationship between a driver's capabilities and the task demand. A driver maintains control over the vehicle and adequate situational awareness if the task demand is within their capabilities. If the task demand exceeds the capability, the situational awareness is endangered and the risk of making errors increases. Changes in mental workload are often assessed using primary or secondary task performance measures: physiological measures, or subjective reflections. This research does not capture the full task demand or the complete capabilities of the drivers, since virtual reality (VR) was used as a research methodology. Consequently, it is unclear what each driver's baseline mental workload is, how it is affected by parallel parking and speed, and whether the increase in mental workload endangers driving performance.
To address this, the term situational workload was introduced in this study. Situational workload captures the influence of road conditions on self-estimated driving performance, self-reported situational awareness, and self-reported workload, based on a combination of subjective reflections and primary task performance measures. The self-estimated driving performance was assessed by evaluating the collision avoidance estimation and the situational awareness was measured by the level of overview on the road. The self-reported workload was complemented by the self-reported level of attention required for the driving task to measure the difficulty of the driving task...