# Speed Reduction Capabilities of Two-Geometry Roundabouts
## 3 Results
### Roundabout Schemes with Variable (y)  
The results of the swept path analyses for the circular movement were the circulatory roadway widths (x) and (y) given in Table 2. The resulting widths along the major axis (x) of analyzed two-geometry roundabout schemes with variable (y) did not meet **Condition 1 (x, y < 5.5 m)**, as they were up to two times wider than the recommended value. This was expected, due to the applied swept path construction. Namely, swept paths for the circular movement were constructed based on a front axle center point path shaped as an arc around the circular central island for a long design vehicle. This arc was constructed with a radius that was offset by 2 m from the roundabout's minor axis. Only one resulting circulatory roadway width along the minor axis (y) was smaller than 5.5 m--the one for the largest analyzed (a) and (b/a = 0.90). At the same time, Condition 1 was met by three standard geometry roundabout schemes with variable (y) and (a = b = 23-25 m), as shown in Table 2.  
**Condition 2 (y < 6.0 m)** was met by 13 two-geometry roundabout schemes with variable (y). At the same time, Condition 2 was met by seven standard geometry roundabout schemes with variable (y) (Table 2). It can be noted that the resulting circulatory roadway width along the minor axis (y) was inversely proportional to the roundabout size, namely, the major and minor axes (a and b). This was not the case with the resulting circulatory roadway width along the major axis (x), as these values for (b/a = 0.75, 0.80, and 0.85) after initial reduction started to rise (Table 2). The results of the swept path analyses for the right turn and straight passage were the distances between the tangent of the entry radius and the tangent of the exit radius along the major and minor axes (L and L\({}^{\prime}\)) and the deflection along the major and minor axes (U and U\({}^{\prime}\)) given in Tables 3 and 4. It can be noted that these distances and the deflections are proportional to the length of the major axis (a). In general, measured distances between  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**a (m)**} & \multicolumn{2}{c}{**b/a = 0.75**} & \multicolumn{2}{c}{**b/a = 0.80**} & \multicolumn{2}{c}{**b/a = 0.85**} & \multicolumn{2}{c}{**b/a = 0.90**} & \multicolumn{2}{c}{**b/a = 1.00**} \\  & **x (m)** & **y (m)** & **x (m)** & **y (m)** & **x (m)** & **y (m)** & **x (m)** & **y (m)** & **x = y (m)** \\ \hline
18 & 11.85 & 7.35 & 10.60 & 7.00 & 9.35 & 6.65 & 8.20 & 6.40 & 6.05 \\
19 & 11.75 & 7.00 & 10.50 & 6.70 & 9.30 & 6.45 & 8.10 & 6.20 & 5.95 \\
20 & 11.75 & 6.75 & 10.45 & 6.45 & 9.25 & 6 the tangent of the entry radius and the tangent of the exit radius along the major axis (L) are larger than measured distances along the minor axis (L\({}^{\prime}\)). The only deviation from this behavior can be noted for a major axis (a) of 24 m and (b/a) of 0.90. At the same time, measured deflections along the major axis (U) are generally smaller than measured deflections along the major axis (U\({}^{\prime}\)). The only deviation from this behavior can be noted for a major axis (a) of 18 m and (b/a) of 0.75. To provide the visualization of the investigation results (given in Tables 3 and 4 and Appendix A, Tables A1 and A2) in as simple a way as possible, 50 simple linear regression models were defined taking the major axis (a) as an independent variable and measured values (L, L\({}^{\prime}\), U, U\({}^{\prime}\), R\({}_{\rm i}\), and R\({}^{\prime}\)\({}_{\rm i}\), where i = 1-3) for different (b/a) relations as dependent variables (Figures 4-8). It should be emphasized here that these simple linear regression models were not intended for use in the two-geometry roundabout's design.