# Tunnel Traffic Evolution during Capacity Drop Based on High-Resolution Vehicle Trajectory Data
## 5 Analysis of Tunnel Driving Behavior
### Analysis of Lane-Change Speed  
The salient feature of a vehicle changing lanes is vehicle speed change. When the driver has an intention to change lanes, he usually takes a deceleration action, waits for the opportunity to enter the target lane, and adjusts his speed in the target lane to enter the stable following state of the target lane as soon as possible. Speed features of lane change vehicles are shown in Figure 5.  
Figure 4: Probability distribution of headway. (**a**) Probability fitting diagram of speed-headway distribution in 3D, (**b**) Probability fitting diagram of speed-headway distribution in 2D, (**c**) Schematic diagram of the headway probability distribution fitting in the synchronous flow state, (**d**) Schematic diagram of the headway probability distribution fitting in the blocked flow state.  
Figure 5: \(Cont\).  
When the capacity decreases, the confluence bottleneck area is in a smooth state. When the driver intends to change lanes, he can quickly adjust his speed and complete the lane-changing behavior faster. At the same time, according to the trajectory characteristics of the previous chapter, the area runs at a higher speed and a more considerable distance. The lane-changing driver has complete space for speed adaptation in a short time and then changes lanes. As the upstream flow increases, the state of this area enters the synchronous flow phase. The deceleration behavior of the lane-changing driver in the original lane decision phase and the speed adjustment behavior in the execution phase cause the following vehicle to adapt to the speed. The disturbance to the following vehicle accumulates over time and ultimately causes the traffic capacity to decrease.  
When the free flow of the study area changes to a congested flow, the lane-changing vehicles in the process of reduced capacity show a similar trend as before the reduced capacity. During this time, the speed exhibits large fluctuations and the fluctuating speed  
Figure 5: Speed features of lane change vehicles.  
of the vehicle during the lane change. The following vehicles cause more significant disturbances, causing the drivers of the following vehicles to vacate a more substantial gap for safety reasons, thus causing a decrease in traffic capacity.  
After the traffic capacity declines, the road shows more severe congestion, and lane-changing vehicles show a low-speed and stable trend. There are significant outliers in the speed box diagram at the lane-changing decision-making stage in this state. After inspection, these outliers are in the upstream input area or ramp, and the congestion state has not spread to this area.  
We further calculate the speed change of vehicles on the target lane and original lane. The speed change rate \(a_{i}\) is the change of vehicle \(i\)'s speed after and before the lane change divided by the original speed. A positive rate indicates that the speed increases after the lane change and vice versa. The results on different lanes are summarized in Table 1. For lane-changing vehicles and following vehicles on the target lane, the speed of most vehicles is reduced during the lane-changing process. The lane-changing vehicle in the outer lane has a more serious speed reduction. When the vehicle changes lanes to the inner lane, its speed increases. The main reason is that the inner lane runs relatively smoothly with less disturbance. The driver of a lane-changing vehicle can better adjust its driving state after entering the inner lane because the speed has increased. For the following vehicle on the original lane, the standard deviation of the parameter is relatively small during the lane change, which means that the original lane is less disturbed, and the speed fluctuation reflected is less.