# Analysis of Conflict Distribution Characteristics between Motor Vehicles and E-Bikes at Roundabouts
## 2 Materials and Methods
### Data Processing  
Traffic conflict is defined as an event involving two or more road users in which the action of one causes the other to make an evasive maneuver [35]. In this research, the conflict between e-bikes and motorized vehicles in the roundabout is defined as motor vehicles or electric bicycles making a maneuver of braking, turning, deceleration, etc. to avoid crashing at the interweaving area or outer circulatory exit lanes at a roundabout. The interweaving area or outer circulatory exit lanes in the area division at a roundabout shown in Figure 3.  
Figure 2: Aerial view of selected roundabouts. (**a**) Zhuque; (**b**) Hanguang; (**c**) Chenyangzhai. How to identify the conflicts between motor vehicles and e-bikes is important for conflict data extracting. The existing methods for identifying traffic conflicts mainly include three methods [36]:  
1. Space Distance Method: Use the distance between both conflict parties as an indicator to judge the severity of the conflict. When the distance between the two is small, the probability of spatial conflict between the two is greater, and the corresponding conflict severity is higher and vice versa. 2. Energy Method: If a vehicle still maintains its existing trajectory, a collision will occur when the trajectory coincides at a certain moment; the degree of conflict is measured by the amount of energy generated at the time of collision. The greater the energy generated by a conflict between vehicles, the greater the severity of the conflict between the two, and, in the same way, the less energy generated by a conflict between vehicles, the less severe the conflict between two people. 3. Time Distance Method: The time is calculated based on the actual distance between the two conflict parties and the speed of them. When the time is bigger than the conflict threshold, it is considered that no conflict occurs. The Space Distance method will cause a large error in the case of low speed, and the Energy Method will be related with the model of vehicles. The Time Distance Method is based on the speed and distance when the two vehicles collide, which is a more scientific way to determine the traffic conflict and is mostly used at intersections. Therefore, in this paper, we selected the Time Distance Method to identify conflicts between motor vehicles and e-bikes. As a conflict indicator of Time Distance Method, _TTC_ (time-to-collision, referring to the time it takes for two vehicles to keep moving on a track until collision occurs without any braking or avoidance behavior at a certain moment before the collision) is selected as the conflict discriminant indicator. Its calculation formula is given by Equation (2):  
\[TTC=\frac{d_{1}}{v_{1}}=\frac{d_{2}}{v_{2}} \tag{2}\]  
where \(d_{1}\) and \(d_{2}\) are the distance of the two vehicles from the conflict point (\(m\)), and \(v_{1}\) and \(v_{2}\) are the original moving speeds of the two vehicles (_m/s_). In this paper, we used _Tracker_ (a video analysis and modeling tool) to extract the trajectory data of vehicles and e-bikes at roundabouts; the average filtering algorithm was used to smooth the trajectory [37]. The specific steps are shown in Figure 4.  
The trajectory smoothing process was performed by the average filtering algorithm. The comparison between vehicle trajectory and speed before and after processing is shown  
Figure 3: Area division of circulatory lanes in a roundabout. The conflict identify formulations are shown in Equation (3). The risk-avoidance behavior occurred when vehicle and e-bike may collide, that is to say at least one of them would stop, increase or decrease their speed, or change the original trajectory. When the absolute value of acceleration is greater than 4 m/s\({}^{2}\) or the direction of movement changes greater than 30 degrees, it is regarded as a risk-avoidance behavior [37]. \[Conflict= \begin{cases}TTC_{a}\leq TTC_{b}+\frac{L_{b}}{V_{b}}\;whenTTC_{a}\geq TTC _{b}\\ \\TTC_{b}\leq TTC_{a}+\frac{L_{b}}{V_{a}}\;whenTTC_{b}\geq TTC_{a}\end{cases}