The Roundabouts itself are traffic control devices. A roundabout is essentially a 4-way intersection with a rotary traffic island in the middle. Signalling where you intend to go while entering — left (left signal), straight (no signal), or right (right signal) — and when you exit, is best practice. Actually, these rules are consistent with other countries. You can try with UK example https://www.gov.uk/…/the…/using-the-road-159-to-203

Thanks Andius. You are right. But, in some countries such as Turkey, China etc., roundabout with signal is a very common application. Actually, I know some reason about this application but I do not want to write it directly. I just wanted to get ideas of other colleaques and researchers and to share it with relevant audience.

Do you mean vehicles signalling their direction intent on approach and while in the traffic intersection with trafficator flashing lights or, red/amber/green traffic lights controlling access of traffic to the intersection?

Yes, Jonathan I mean traffic lights on each arm of the intersection and around the center of roundabout. This is a typical application in some countries, like China, Turkey etc.

Yetis, now I understand. The problem you have can be worked on using fluid-flow analogies. Streamline and turbulent flow. Not my work but what I have read elsewhere. Relates to flow capacity of roadways, vehicle density, flow speeds. With a roadway for a given set of vehicle speeds is conveying less than a critical “amount” of traffic the flow has the analogy of streamline flow and everything goes smoothly. As the flow conditions change, vehicle speed, vehicle density, change of flow capacity due to a junction or a road incident (perhaps as innocent as a vehicle parked at the side of the road) the flow will flip into turbulent flow giving a bottleneck and a jam.

Road junction engineering understands the flow capacity limitations at significant points in the journey (perhaps over as little as 100m) and works to manage the flow to maintain or restore streamline flow through the junction.

This can include flow management measures quite a way upstream so that the flow at the bottleneck/pinchpoint is streamline and maximised.

The challenge for road engineers is to convey these concepts to tired and frustrated drivers who might be several miles away from the pinch point that will delay their journey....

Understsnd Bernouli’s equation and Reynolds numbers and apply them to road traffic situations. Different fluids compares to different mixes of heavy vehicles, light vehicles, motorcycles and bicycles, differential vehicle speeds and vehicle spacing.

A fascinating project - perhaps for certain people only!

regsrds, Jonathan

Dear Prof. Dr. Yetiş Şazi Murat firstly thank you for your kindly question. As you know in our country, utilization of signalized roundabouts (but their geometry is not a roundabout, most of them are traffic circles) is very common from the traffic authorities. But we have a big problem about intersection geometry. Unfortunately, we don t have an original roundabout geometry standard for Turkey. Traffic authorities generally use other countries' standards or in some situations they do not use a standard. For this reason, we have generally seen lane indiscipline and complexity in signalized and unsignalized intersections. That's why, firstly we must determine the most suitable geometry for the examined urban roads. Then we should observe many parameters from these intersections to decided full signal utilization. But in Turkey, if there are high density traffic circulations at roundabouts (most of them traffic circle), limit and control driving behaviors with unsignalized traffic warning signs is not possible. Because our drivers are generally have an aggressive driver profile and they generally want to move fast. For this reason, if we do not manage and control traffic flow, we can use full signal in a unsignalized roundabout organize to limit and control the complexity. In summary, we can conclude that driver characteristics and roundabout geometry have great effect to choose full signal control for Turkey. In different countries, we can see different parameters to decide full signal control. I think the answer of this question can change according to different parameters of different countries.

Best regards...

Metin

Roundabouts are recommended for low traffic volumes and density , while traffic signals are provided and proved to be more suitable for high traffic volumes.

Regards

Zainab

Have a look at the AUSTROADS roundabout guides as well as the UK guides on signalising roundabouts. It depends on how big the roundabout is, the ones in the UK tend to be roundabouts at interchanges . This is a complex analysis problem that can be solved using Arcady, Transyt software or any microsimulation model. The problem would be to calibrate it correctly for queue lengths as these will be critical in analysing the phase times that would work. See the attached manual on a design course for these types of intersection.

Dear Urie,

Thank you very much for your comments and your document share. This application is very common in some countries, but many colleaques need guidance before design. Because of that I just wanted to start this discussion and to get some feedback in worldwide.

Dear murat

In case the road users are not respecting the function of roundabout which the road users should always give priority to vehicles entering the roundabout

Dear Şazi,

I agree with most of the comments above, especially comments from Metim Mutlu AYDIN. However, siganlzied roundabouts, especially when they are corretyly designed, may provide better performance then four-legged siganlzied intersections where left turning movements are allowed. In İzmir, all the intersections on an arterail are designed as signalized roundabouts and they provide acceptable performance even there is a high left turning flow from one direction. You can decrease number of phases in a cycle (you can define a two phase plan) and this may help you to gain haigh capacity and low delay vakues.

Dear Serhan,

Thank you very much for your comments. I think, left turning volumes and driver behaviours are the main factors of the performance. On the other hand, the storage area around the circle may have a significant effect.

Roundabouts should never be planned for metering or signalization. However, the guide does concede that “unexpected demand” may require signalization after a roundabout is constructed. Three signalization alternatives to be considered should unexpected demand suggest the need for signals: (1) metering, (2) nearby pedestrian signals, and (3) full signalization of the circulatory roadway. Full signalization is required only where traffic demand far exceeds the demand at locations where modern roundabouts would be considered for new construction. The primary requirement for fully signalized roundabouts, is the capacity to store stopped vehicles in the circulatory roadway without creating queues that spill back to block upstream exits or entries.