Assessment of Roundabout Capacity and Delay

Based on three decades of research and development by TRL, ARCADY is used to predict capacities, queues, deltas and accident risk at roundabouts. An easy-to-use tool for the busy traffic professional wanting to design new roundabouts and assess the effects of modifying existing sites. Available as a Roundabout module in Junctions 10.

Roundabouts are modelled using the well-established TRL/Kimber capacity relationships (the ARCADY Model), which take into account key roundabout geometries such as entry width, approach width, flare length, conflict angle, inscribed circle diameter and entry radius. This empirical framework intrinsically links roundabout geometry to driver behaviour and in turn to predicted capacities, queues and delays. 

ARCADY has been successfully used to design and improve a number of roundabouts throughout the world. It has a host of satisfied customers including governments, multinational organisations and academic institutions. It’s simple and intuitive interface means that it can be used effectively by everyone, in a relatively short space of time. 

What does ARCADY Model?

  • Roundabouts 
  • Mini Roundabouts 
  • Linked Roundabout Networks 
  • Large or Grade Separated Roundabouts 
  • Pedestrian Crossings (Signalled, Unsignalled and Adaptive) 
  • Priority or ‘first-come-first-served’ chicanes

Lane Simulation

An established Lane Simulation tool, first introduced in ARCADY 8, allows simple simulation of individual lanes to be performed on existing ARCADY models. The user can quickly see where unbalanced queuing may occur and if lane starvation may take place. The simulation takes into account the geometric layout of the roundabout, turning proportions and user-specified lane designations. Lane movements can then be altered easily using the roundabout diagram to explore and identify the optimum lane configuration. 

When combined with OSCADY, it is possible to set up and model part signalised roundabouts, including signals on circulating lanes.

Features in the ARCADY Module

  • (Average) arriving vehicle delay 
  • Auto-updating summary results 
  • Site-specific capacity adjustments  
  • Multiple geometric layouts, time periods and design years in one file 
  • Point-to-point journey times 
  • Built-in Geometric Measuring tool assists data entry 
  • Choice of HTML, Word and PDF outputs, including customised output

How ARCADY works

  • The program uses the geometric parameters of the roundabout with the traffic flows to predict queue, delay and capacity 
  • Additional results such as geometric delay and accident prediction are also available 
  • The geometric parameters and the controlling flows, split into smaller time periods, are used to calculate the capacity of each priority approach. The queues and delays are then calculated for each time period, using time dependent queuing theory. 
  • The ARCADY model is an empirically derived one, based on extensive data sets collected at existing junctions.

Current Version: 10.0.4 Version History

System Requirements:

Windows 7 or above

Supported Browsers:

Google Chrome (latest version)
Mozilla Firefox (latest version)
Microsoft Edge (latest version)

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