Recently, we did a simulation of the roundabout in Peshawar, Pakistan by PTV Vissim due to the proposed roundabout faced delays and queues on a daily basis at peak hours, which we did to simulate the actual geometric design of that roundabout by collecting the data of vehicles passed through that specific roundabout by providing U-turns at every route before vehicles reaching for U-turns just in the roundabout. what we noticed is that these U-turns does not only provide smooth flow but also it increases the Level of Service from D to A. Therefore, we concluded in our paper that by providing U-turns on every route before vehicles reached to U-turns, can improve Level of Serviceability of any roundabout.
Has anyone done similar research? If so, what have you found?
Good idea! Low cost level of service improvement. Looks like a candidate for useful universal information to include in the ASSHTO GDHS after your research is able to produce an application level design guide. Yes, as Fraser Howe states there are many things to consider. Not the least of which are approach speed, exit taper, turning path , entrance taper, flow gap, stacking capacity, sight distances, grades, weather conditions, and other design features normally used for intersections. Signage and enforcement would be included, as well as driver population characteristics (aggressive, moderate, casual). Most likely prohibit trucks, buses and pedestrians. Maybe bicycles as well.As with the normal GDHS presentations, please convert your simulations and research to practical NCN style (no computer necessary) designer-friendly tables, diagrams, and verbiage. NCN style is best and quickest way for an experienced geometric designer to sketch before CADemizing it.I think an important factor missed by many designers is the 2-second rule of roadway conditions changes. That is, try to provide a minimum of 2 seconds and as much as 6 seconds minimum driving time between roadway condition changes (such as lane width, lane drops, shoulder width, or other geometry) in order for the driver to adjust to the new condition. Example distances are shown in the GDHS Decision Sight Distance tables. This rule should determine the minimum distance needed between the u-turn and the roundabout.Hope you get some good help on your project.