How to Design A Roundabout (Horizontal Design)

Disclaimer: This video is for educational purposes only...
Upon many requests from my previous tutorial videos and colleagues...
This video shows the steps of HOW to Design A Typical Roundabout using Microstation (a Bentley Systems Product) as a CAD program, the following steps are included in this video:
1) Developing intersecting roads with a median of 6m in width and two lanes of 3.65m in width for each lane in each direction.
2) Developing a roundabout with inscribed diameter (ICD) of 50m.
3) Developing the approaches (Entries and Exits) with curves of R=25m and lane widening to 4m.
For any queries, please contact [e-mail]

[@patcalasukal]

why did you use 25unit radius in the entry and exit curves?

[@ImadBalich]

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).

[@patcalasukal]

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!

[@ImadBalich]

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...