## 2 Literature Review  
In the reverse lambda fundamental diagram suggested by [PERSON] and [PERSON] [21], the congested branch does not reach the maximum point compared to the uncongested side. The discontinuity is the capacity drop phenomenon. Previous studies give the value of the capacity drop between 0.5 and 35% of the pre-queue capacity. In those studies, traffic data are collected from bottlenecks such as merges, lane reductions, and horizontal curves. The following are the causes and relationships found by researchers related to the capacity drop:  
* The capacity drop is caused by variance-driven gaps, which is the difference in time headways adapted by drivers [22];
* Due to lane changes on the highway, voids are created. This is the cause of the capacity drop together with speed in the congestion [23; 24];
* The density near the bottleneck is highly correlated with the capacity drop. Once the critical density is reached, the capacity drop can be expected [10];
* The number of lanes is a critical influencing factor of the capacity drop. If there are more lanes, the drop decreases due to the drivers having more options for lane changing [11];
* The higher the on-ramp flow, the larger the capacity drop is [12];
* The value of mainline flow divided by ramp flows has a significant effect on the level of the drop [12];
* The capacity drop can differ depending on the type of congestion upstream [25];
* Variable driver characteristics cause traffic hysteresis for different drivers and have an impact on the development of traffic oscillations and the bottleneck discharge rate, which causes the capacity drop. This indicates that driving behavior is different for drivers before they enter the congestion compared to after they come out of the congestion [26];
* Vehicles' speed in congestion seems to have a linear correlation with the queue discharge rate [13];
* Lane-changing behavior is not more of a reason for the capacity drop than the type and severity of congestion upstream [27];
* Spatially distributed lane changing contributes to the capacity drop [28];
* The relationship between the capacity drop and on-ramp ratio, which is the on-ramp traffic flow divided by the on-ramp traffic flow plus the upstream traffic flow at a given interval, is a convex quadratic polynomial [15]. \"The main cause of the capacity drop is not identified yet. Some argue it is lane changing, others argue it is the limited acceleration, whereas others argue it is the difference in acceleration. This remains an active field of research, both for causes of the capacity drop and for ways to control it\" [29]. While several pieces of research were already conducted about the capacity drop, there are still empirical characteristics that are unknown. Table 1 summarizes the existing knowledge about the capacity drop, showing weather condition considerations. This paper will answer the gap in previous studies on capacity drop, which excludes the effects of rainfall. Most of the studies presented in Table 1 do not mention bad weather conditions. It is assumed that the data gathered in those research were during clear weather conditions. Others specifically mention data gathering during clear skies and no measurable precipitation, such as [PERSON] and [PERSON] [6]. [PERSON] and [PERSON] [8] specified that data were gathered during dry and sunny conditions except for one day when light rain was experienced. Nevertheless, they considered the event negligible and used the data in the analysis. In the literature, two papers specifically mentioned gathering data under bad weather conditions [10; 13]. These two papers will be discussed in detail. [PERSON], [PERSON], and [PERSON] [10] studied the relationship between density, which is the accumulation of vehicles in the shoulder lane, and the capacity drop near a bottleneck on three different bottleneck sites. They concluded that density is a good predictor of the capacity drop. When a certain threshold is reached, the capacity drop can be expected to happen. They called this the critical density.