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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 9.0.0 / May 2015
Operating system Windows (XP / Vista / 7 / 8)
Type Traffic Software
License Software license agreement
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 which were 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.

ARCADY is listed 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.
  • TD 16/93, Geometric Design of Roundabouts, U.K. Department for Transport, 1993.

Recent developments[edit]

From ARCADY 7 onwards, the software has been capable of communicating with CAD vehicle swept path software AutoTrack. This aids real-time design analysis. ARCADY and AutoTrack Junctions are linked and communicate automatically, in real, time any changes in geometry that are made in CAD and the roundabout analysis results that are provided by ARCADY.[3] AutoTrack Junctions creates roundabout models to applicable national standards with splitter islands, crossings, rumble strips, speed striping, sight distances and crown lines. The Link between the two software packages was originally released in early 2011[4][5][6] to analyse capacity issues directly against safety issues in the roadway design process as the two factors, traffic capacity and safety risk, can often have negligible effects on the other. The link was only accepted by the traffic engineering community as ARCADY utilises full geometric data to analyse traffic capacity and so can communicate the relevant CAD data such as angles and linear/ tangential distances.

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

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

ARCADY 8 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.


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.


External links[edit]