Pat Calderon there are many Roundabout design guidlines and standards that talk about the entry and exit curves, some share the same concepts and some differ depending on the region. Yet, in general Entry curves have a great influence on the operation, safety and capacity of a roundabout, thus, the larger the Entry curve (up to 20m to 25m) the better is the capacity, but, the speed is also an important factor that should be looked at. The Exit curves have also an influence on the operation and safety of roundabouts, some guidelines mention that it's a good practice to keep Exit curve not smaller than the circulating curve, and not significantly greater; to ensure low speeds at the downstream pedestrian crossing (if available).
Thanks! I am designing a roundabout with five legs and I am finding a hard time deciding on which entry radius and exit radius I should use. I simulate with Vissim 10 and it shows no drastic improvement. I will try to enlarge the inscribed circle diameter to have a larger entry/exit curve as you said it will have better capacity. Our guidelines limits the entry radius to be less than the central island radius. Again, thanks!
Pat Calderon What governs the Entry and Exit Radii is the Inscribed Circle Diameter (ICD), as you said earlier you should choose an appropriate ICD for your roundabout which is mainly a function of two factors, the design vehicle (Passenger car (16m), Single-Unit (29m), WB-12 (30m), etc...) and the allocated area available... You're welcome... Wish you all the best...
why did you use 25unit radius in the entry and exit curves?
Pat Calderon there are many Roundabout design guidlines and standards that talk about the entry and exit curves, some share the same concepts and some differ depending on the region.
Yet, in general Entry curves have a great influence on the operation, safety and capacity of a roundabout, thus, the larger the Entry curve (up to 20m to 25m) the better is the capacity, but, the speed is also an important factor that should be looked at.
The Exit curves have also an influence on the operation and safety of roundabouts, some guidelines mention that it's a good practice to keep Exit curve not smaller than the circulating curve, and not significantly greater; to ensure low speeds at the downstream pedestrian crossing (if available).
Thanks! I am designing a roundabout with five legs and I am finding a hard time deciding on which entry radius and exit radius I should use.
I simulate with Vissim 10 and it shows no drastic improvement. I will try to enlarge the inscribed circle diameter to have a larger entry/exit curve as you said it will have better capacity. Our guidelines limits the entry radius to be less than the central island radius.
Again, thanks!
Pat Calderon What governs the Entry and Exit Radii is the Inscribed Circle Diameter (ICD), as you said earlier you should choose an appropriate ICD for your roundabout which is mainly a function of two factors, the design vehicle (Passenger car (16m), Single-Unit (29m), WB-12 (30m), etc...) and the allocated area available...
You're welcome... Wish you all the best...