# Speed Reduction Capabilities of Two-Geometry Roundabouts
## 3 Results
### Roundabout Schemes with Variable (y)
The modeled simple linear dependency of the distance between the tangent of the entry radius and the tangent of the exit radius along the major axis (L), the distance between the tangent of the entry radius and the tangent of the exit radius along the minor axis (L\({}^{\prime}\)), the deflection along the major axis (U), and the deflection along the minor axis (U\({}^{\prime}\)) and the major axis length (a) for roundabout schemes with variable (y) is shown in Figures 4 and 5. It can be noted that the parameters (L) and (U) were significantly influenced by (a) for every designed roundabout scheme with variable (y), while this dependency is less significant for the parameters (L\({}^{\prime}\)) and (U\({}^{\prime}\)), especially for (b/a = 0.80) and (b/a = 0.90a). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \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**} \\  & **L\({}^{\prime}\) (m)** &  
Figure 4: The linear dependency of the distance between the tangent of the entry radius and the tangent of the exit radius (L and L\({}^{\prime}\)) and the major axis length (a) for roundabout schemes with variable (y). Figure 5: The linear dependency of the deflection (U and U\({}^{\prime}\)) and the major axis length (a) for roundabout schemes with variable (y). Figure 6: The linear dependency of the entry path radii (R\({}_{1}\) and R\({}^{\prime}\)\({}_{1}\)) and the major axis length (a) for roundabout schemes with variable (y). Figure 7: The linear dependency of the circulating path radii (R\({}_{2}\) and R\({}^{\prime}\)\({}_{2}\)) and the major axis length (a) for roundabout schemes with variable (y). The calculated vehicle path radius (R) and measured personal vehicle fastest paths radii Ri and R\({}^{\prime}\)i (i = 1-3) for the variable circulatory roadway width along the minor axis (y) are given in Appendix A, Table A1. The modeled simple linear dependency of the personal vehicle's fastest path radii (R\({}_{\rm i}\) and R\({}^{\prime}\)i, where i = 1-3) and the major axis length (a) for roundabout schemes with variable (y) is shown in Figures 6-8. It can be noted that:  
* radii for (b/a = 0.75) showed the greatest discrepancy caused by large path radii values in roundabouts with the smallest major and minor axes,
* for (b/a = 1.00), either no influence could be noted, or radii were inversely proportional to (a), and
* for the rest of the roundabout schemes, either no influence could be noted, or radii were proportional to (a). Analyses of the vehicle path deflection around the central island have shown that **Condition 3 (D > 7.00.m)** was met by 88% of the designed two-geometry roundabout schemes with variable (y) and by all standard roundabout schemes with variable (y) (Appendix A, Table A2). Condition 3 was not met by the two-geometry roundabouts with the smallest major and minor axes:  
* major axis (a) of 18 m and (b/a = 0.75, 0.80), and
* major axis (a) of 19 and 20 m and (b/a = 0.75). **Condition 4 (R\({}_{\rm 1}\) < 100 m)** was not met by one analyzed two-geometry roundabout with variable (y) (Appendix A, Table A1): the one with a major axis (a) of 18 m and (b/a = 0.75) for both directions. This condition was met by all analyzed standard roundabout schemes. The results of the calculation of the expected driving speed through the roundabout (V) for the major and minor axis directions of each roundabout scheme, which was conducted according to Equation (3), showed that **Condition 5 (V < 35 km/h)** was not met by all analyzed roundabout schemes with variable (y) (Appendix A, Table A2).