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Junctions is a software package by Transport Research Laboratory incorporating the ARCADY and PICADY modules which were previously separate programs. "Junctions 8" was the first integrated version.


Developer(s) Transport Research Laboratory
Stable release
9.0.1 / November 2015
Operating system Windows
Type Traffic software
License Proprietary software
Website http://www.trlsoftware.co.uk/ARCADY
ARCADY is used to assess roundabout designs.

ARCADY is the acronym for (Assessment of Roundabout Capacity And DelaY). This software, produced by the Transport Research Laboratory (UK), models traffic capacity, queues and delays at roundabouts. The software is largely based on empirical relationships between roundabout geometry and capacity, which were established as the result of extensive research carried out on existing roundabouts on the UK road network, as well as controlled test track facilities over a period of over a decade.[1]

The program is used by traffic engineers when assessing existing layouts or when analysing the impacts of proposed design changes. Estimates of annual accident frequencies can also be obtained.

The capacity and safety relationships which ARCADY utilises are discussed in the UK's Design Manual for Roads and Bridges.[2]

RODEL is similar to ARCADY and utilises TRL equations under licence from TRL.

Papers on ARCADY:

  • Kimber, R.M., The Traffic Capacity of Roundabouts, TRL Laboratory Report LR942, 1980.
  • Maycock, G. and R.D. Hall, Accidents at 4-Arm Roundabouts, TRL Laboratory Report LR1120, 1984.

Recent developments[edit]

From ARCADY 7 onwards, the software has been capable of communicating with certain CAD software, aiding real-time design analysis.

ARCADY 7 introduced the ability to model simple networks of linked roundabouts.

In ARCADY 8, the HCM 2010 methodology for roundabout analysis was made available.

ARCADY 8 also introduced a simulation technique to deal with the modelling of certain configurations such as lane usage at roundabouts.

'ARCADY Lite' is a simplified version of ARCADY 8 that provides basic analysis of roundabouts.

ARCADY 9 includes built-in tools for graphically measuring roundabout geometries and for assisting with the transfer of traffic flow data from other sources (typically spreadsheets).


PICADY is used to assess priority junction designs.

PICADY (Priority Intersection Capacity and Delay) is a program for modelling three and four arm priority junctions in a similar manner to ARCADY. It is based on empirical relationships which link capacity and safety with various geometric attributes of junctions such as road widths and visibilities. These relationships are discussed in the UK's Design Manual for Roads and Bridges.[3]

PICADY 9 also includes HCM 2010 models for TWSC and AWSC intersections.

Papers on PICADY:

  • Kimber, R.M. and R.D. Coombe, The Traffic Capacity of Major/Minor Priority Junctions, TRL Laboratory Report SR582, 1980.


External links[edit]