## 2 Materials and Methods  
A list of symbols used in the manuscript is given in Table 1.  
The geometric parameters of a roundabout are the outer radius (R\({}_{0}\)), the central island radius (R\({}_{i}\)), the circulatory roadway width (u), the number of legs (j), the angle between the legs (8), entry width (e), exit width (e\({}_{i}\)'), entry radius (R\({}_{j}\)), and exit radius (R\({}_{j+1}\)'). The selected R\({}_{0}\) is influenced by the location of the roundabout (urban, suburban, rural), roundabout task (e.g., traffic calming), spatial constraints, and the number of circulatory lanes. In this investigation, the roundabout geometric parameters, design vehicle used for swept path analysis, and traffic flow characteristics were defined based on the following assumptions: (1) the roundabouts were to be situated in a suburban environment and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Group** & **Symbol** & **Parameter** \\ \hline  & R\({}_{o}\) & outer radius (m) \\  & R\({}_{i}\) & central island radius (m) \\  & u & circulatory roadway width (m) \\  & j & number of roundabout legs, j = 1,..., 4 \\  & \(\delta\) & angle between the roundabout legs (\({}^{\circ}\)) \\ Geometric & 1 & length of the arc between the adjacent roundabout legs (m) \\ parameters & e\({}_{j}\) & entry width (m) \\  & e\({}_{j}\) & exit width (m) \\  & R\({}_{j}\) & entry radius (m) \\  & R\({}_{j+1}\)\({}^{\prime}\) & exit radius (m) \\  & b\({}_{j}\) & distance between exiting and entering traffic flows along the center of the circulatory lane (m) \\ \hline  & i & direction of travel through roundabout, i = 1,..., 12 \\  & q\({}_{i}\) & traffic flow in the direction i (veh/h) \\  & Q\({}_{i}\) & traffic flow in passenger car units in the direction i (pcu/h) \\  & f\({}_{T}\) & conversion factor for traffic composition (pcu/veh) \\  & Q\({}_{Cj}\) & circulating traffic flow (pcu/h) \\  & Q\({}_{Sj}\) & exiting traffic flows at leg j (pcu/h) \\  & Q\({}_{Ej}\) & entering traffic flows at leg j (pcu/h) \\ Traffic & BC\({}_{j}\) & base entry capacity of the roundabout at leg j (pcu/h) \\ parameters & f\({}_{P}\) & capacity reduction factor for pedestrian and cycling traffic flow at roundabouts (-) \\  & C\({}_{Ej}\) & entry capacity at leg j (pcu/h) \\  & C\({}_{mj}\) & entry capacity for mixed traffic flow at leg j (veh/h) \\  & q\({}_{mj}\) & mixed traffic flow at leg j (veh/h) \\  & x\({}_{mj}\)\({}_{A}\) & degree of saturation of entry at leg j according to analytical model (-) \\  & x\({}_{mj}\)\({}_{R}\) & degree of saturation of entry at leg j according to regression model (-) \\  & \(\alpha\) & factor reflecting the impact of exiting traffic on entry capacity by distance b (-) \\  & \(\beta\) & factor for adjusting circulating flow depending on the number of circulating lanes (-) \\  & \(\gamma\) & factor for adjusting entry capacity depending on the number of circulating lanes (-) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of symbols used in the manuscript. (2) the roundabouts were to act as single-lane traffic-calming devices along the transition path from the rural to the urban environment. A plan view of the analyzed 4-legged single-lane roundabouts schemes was created in AutoCAD. The following initial geometric parameters were used (Figure 1a):  
* R\({}_{\text{o}}\) applied in this investigation varied from 13.0 to 20.0 m, with a 0.5 m increment. According to previous research given in [22], these outer radii are commonly used for single-lane roundabouts worldwide. An increment of 0.5 m was chosen to capture the dispersity of the results and to create a sample that is representative, manageable, and easy to present at the same time;
* The roundabout leg alignment was radial, as is standard in the suburban environment [22];
* The axes of legs 1 and 4 intersected at \(\delta\) = 90\({}^{\circ}\). The axes of legs 1 and 2 intersected at \(\delta\) ranging from 75\({}^{\circ}\) to 90\({}^{\circ}\) with 5\({}^{\circ}\) increments.