Priority Junction Operation and Capacity Analysis


Endorsed by CIHT for CPD
IHE Approved CPD

Chartered Institute of Highways & Tranportation logo Institute of Highway Engineers logo

The basic skills traffic engineers and planners need include understanding how junctions work, and how to assess how they will perform in practice. Traffic engineers and planners also need to be able to understand the limitations of such analyses. The most common way of assessing priority junctions and roundabouts is by using PICADY or ARCADY - industry-standard computer analysis packages. This course provides a basic understanding of how T-junctions, crossroads and roundabouts operate and are designed, including the principles of priority control on which the assessment methodology is based. It then shows delegates how these principles operate in PICADY and ARCADY. Going further than this, it allows delegates to discover from their own work during the course, how important it is to be accurate in specifying the input data, and what the consequences of inaccuracy may be.

Aims & Objectives:

The course aims to provide delegates with:

  • guidance on choosing the type of priority junction in different circumstances
  • an understanding of the advantages and disadvantages of each junction type, including safety issues
  • an introduction to DfT geometric layout standards
  • the basic information needed to design priority junctions
  • an understanding of how ARCADY and PICADY can be used to predict existing and future performance of priority-controlled junctions

On completing the course delegates should:

  • understand how priority-controlled junctions and roundabouts operate
  • know the principles of selecting an appropriate form of priority control for different situations
  • know how the capacities of such junctions can be assessed
  • understand the main functions and facilities of PICADY and ARCADY
  • be able to prepare basic geometric and traffic input data for PICADY and ARCADY
  • understand the need for accuracy in preparing input data
  • be able to identify whether or not a chosen design will have sufficient capacity to cope with predicted traffic demand

Course Outline:

Course Outline:

  • Introduction
  • Overview of course
  • Priority junction operation (Background; basic principles; forms of junction; advantages/disadvantages of each form)
  • Choosing the most appropriate form of junction in a given situation
  • Practical - individual work to select best solution for two scenarios, followed by group discussion
  • Factors affecting junction and roundabout capacity
  • Design procedures (assessing capacity; principles of design; information needed for design)
  • Predicting capacity of priority junctions PICADY overview; preparing input data; practical: investigating variability inherent in preparing geometric data; demonstration of running PICADY to show how input variability affects results; discussion
  • Predicting capacity of roundabouts ARCADY overview; preparing input data; practical: investigating variability inherent in preparing geometric data; demonstration of running PICADY to show how input variability affects results; discussion
  • Discussion and questions
  • Recap on course and pointers for further learning

The course uses a combination of:

  • presentations
  • discussion sessions
  • group and individual practical activities and
  • demonstrations of PICADY and ARCADY output to show how this can vary if input data are not prepared accurately.
  • comprehensive briefing in issues relating to understanding priority junction operation and assessment methods
  • introduction to use of PICADY and ARCADY
  • understanding of need for accurate input data to deliver realistic assessments
  • a good introduction to junction design

Intended For:

  • New graduates/technicians with little or no practical traffic engineering experience
  • More experienced staff taking up new responsibilities in traffic engineering and development planning, and looking for a briefing on this topic

Course does not require any prior knowledge.

All delegates need to bring the following to the course: pencil, eraser, ruler, protractor and scale rule and a pair of compasses.