Software and Innovation

Ourston Roundabout Engineering is North America's official training center for roundabout design software. We provide training and support for the following software packages:

• ARCADY 7: TRL's software program for the assessment of roundabout capacity, delay and safety at standard, mini and grade-separated roundabouts.
• AutoTrack: Vehicle swept path and turn simulation software which models the swept paths of all types of steered vehicles.
• RODEL: A DOS-based roundabout design software package developed by Robert Barry Crown.
• VISSIM: The leading microscopic simulation program for multi-modal traffic flow modeling.

Looking for upcoming software training and workshops?
View our workshop schedule or contact us to schedule a workshop.

Operational Analysis

Ourston Roundabout Engineering, Inc. recommends the software programs ARCADY 7 and RODEL because the programs give our designers a direct link to the researched prediction models governing geometric sensitivity of safety and capacity. These programs are helpful tools for aiding roundabout design. The purpose of ARCADY 7 and RODEL is to:

• Improve design quality
• Drastically reduce design time
• Reduce land and service costs
• Allow rapid exploration of many options especially with respect to safety
• Derive the optimum layout within the conflicting constraints of cost, delay and safety

ARCADY 7  and RODEL are based on the empirical capacity equations developed through extensive experiments at the Transport Research Laboratory in the United Kingdom. Rather than simply checking designs after they have been drawn, ARCADY 7 and RODEL generate geometry prior to scheme drawing. This avoids the time consuming practice of repeated drawing and checking. ARCADY and RODEL allow the designer to optimize a balanced design in respect to delay, safety and cost.

The empirical models found in ARCADY 7 and RODEL are derived from extensive research, and with simple calibration are proven accurately predict roundabout capacity at all ranges of traffic flows.  Arcady 7 allows for calibration to the recent NCHRP 3-65 research on U.S. roundabout capacities. 

Other roundabout analysis programs use gap-acceptance models that are not empirically proven. Gap-acceptance theory is familiar to transportation professionals from sources such as the Highway Capacity Manual. Capacity is predicted based on the size in time of the gaps between successive vehicles motorists choose when entering a major traffic stream, such as the circulating flow of a roundabout. The gap-acceptance time can be calibrated to reflect differences in motorist behavior between countries.  Unfortunately, gap parameters vary according to traffic flow and are difficult to measure.

Gap-acceptance models can adequately predict roundabout capacity within certain ranges of traffic flows. However, outside these ranges gap-acceptance models can over-predict capacity at low traffic flows and under-predict capacity at high traffic flows. At low flows, motorists often react to enter a major traffic stream more slowly. At high flows, “gap-forcing” and “priority reversal” take place, which are not explained well by conventional gap-acceptance theory. These phenomena are described in a paper by the TRL’s R.M. Kimber entitled Gap-Acceptance and Empiricism in Capacity Prediction (Transportation Science, Vol. 23, No. 2, 1989).

Microsimulation

Ourston has extensive experience in Micro-simulation; utilizing programs such as VISSIM. Ourston has produced complex micro-simulations for analysis and public presentation. Simulation is an effective way to evaluate interaction between intersection control types such as corridors of roundabouts, or roundabouts and traffic signals. Other key benefits include assessment of weaving and merging behaviors between intersections.

The VISSIM model produces a qualitative depiction of the analysis of a corridor to compare operational impacts of alternative traffic controls but has limitations. It is immensely important to understand the capabilities of micro-simulation programs.  Calibration is difficult if not impossible for high demand situations with complex multi-lane roundabouts.  Thus, we use this tool as an indicator of a problem relative to the corridor but not for absolute values of queuing and delay.  Nevertheless it is a valuable tool for public displays and discussions.