User Guide > Introducing Rodel

Introducing Rodel

Rodel is a fully interactive program for the Planning, Design, Evaluation and Analysis of Roundabouts. 

The primary input and output is displayed in a single window and input data can be edited and the results viewed in the same window during a three-second cycle. This is very educational and develops a good understanding of the relationships between geometry and capacity; all input and output is either in the single main window or in sub windows one mouse click away, making navigation extremely simple. The use of confusing nested windows has been strenuously avoided.

Mode 1, the Planning Mode, uses minimal existing geometric data together with an estimated outer circle diameter to generate geometric options that achieve Target Delay, Queue or Volume Capacity Ratios for each leg. Geometric options are derived for each leg providing alternative layouts. A geometric option is selected for each leg that provides the best fit within available constraints while achieving the desired Target Delays, Queues or Levels of Service, while minimizing accidents.

Mode 2 is used for finalizing the Evaluation and Analysis. A more refined design starts with the selected geometry from Mode 1 and refines the geometry, tailoring the design to the objectives. Usually objectives compete and Rodel enables designers to find the optimum trade-off between competing objectives. Mode 2 uses six geometric parameters for each leg to derive entry capacity. Rodel's interactive user interface plus the strong relationships it shows between capacity and geometry lead to unique design solutions.

All the parameters have a pop up summary called by clicking on the parameter name. The Geometric parameters also have graphical input that is selected by clicking any of the name of the Geometry Grid. The data input graphically automatically update the data in the grids.

Rodel is a dynamic model and instead of modeling the peak hour as a whole, using and producing hourly data, Rodel divides the peak hour into small time slices and models each slice in turn. This provides the evolution of Flows, Capacity, VC Ratios, Queues, Delays and LOS over the hour as well as hourly averages. The evolution of queues is especially useful for checking if queues block back critically for all or part of the hour. This High Definition Queuing Theory also allows for accuracy in Queue and Delay predictions at high v/c conditions up to and exceeding 1.0.

Peak hour arrival flows are reshaped into a rise and fall profile using three methods including the Peak Hour Factor method.

The model supports both Left Hand and Right Hand driving and allows either English or Metric units for geometric definition.

It includes extensive Error, Warning and Caution checks that display messages to help and guide the user, including the assessment of approach and exit road capacities, warning the user if arrival or exit flows reach or exceed these capacities, as it is unnecessary to design for flow levels that cannot reach or exit the roundabout.

A Scheme Notes utility has been added to enable key information to be recorded with the scheme data. This can be used to record the evolution of the design, especially key decisions and to communicate this information to other Planners, Designers, Analysts or Clients. These notes are included in the printout together with any outstanding Warning or Caution messages.

A recent addition is the explicit modeling of all types of bypass lanes. The model includes the interaction between yield line entry capacity at the roundabout and the bypass lane capacity when they do not have separate approach lanes, but share the approach width partially or fully.

Three accident models are included. There are Intersection Level Models that use global intersection geometry and flow data and Approach Level Models that use detailed entry geometry and detailed turning flows. A range of models is used from NHCRP Report 672 "Roundabouts: An Informational Guide" and also the UK Injury accident models. The user can select any model and can compare their results.

Arrival Turning Flows for the am peak, off peak and pm peak are modeled in a single Rodel file and the results used to derive annual delay costs and annual accident costs for Economic evaluation.

The output is on tabbed fields. Any field can be active while the others are one mouse click away.


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