Abstract :
Vihdintie roundabout is a five-arm conventional roundabout with some 140 m in diameter. It is located in a western suburban area in Helsinki and it connects three important main roads together. A theoretical five-arm roundabout signalling model was studied with Transyt. Only the offsets and splits were optimised. A cycle time of 60 seconds was chosen because of analytical considerations. The size of the roundabout was chosen so that the travel time round the system was assumed to be 40 seconds. The study shows that the optimisation of timings with Transyt is very useful, especially the possibility of handling all traffic streams separately with the shared stopline-option. Traffic actuated control mode is suitable for roundabout signalling. Some special control logic should be used, which maintains the good progression of vehicles through adjacent stoplines
