RFC output in Lane Simulation Mode – Junctions 10

“RFC – Common ground for all”

Can anyone guess what the following documents have in common – “TA 23/81 – Junctions and Accesses: Determination of Size of Roundabouts and Major / Minor Junctions (1981)” ; TD16/93 – Geometric design of roundabouts (1993)”; “AG74 – Junctions 10 User Guide (2023)” – apart from all being related to UK unsignalled junction design? The answer is that somewhere within their text they all refer to the ratio of flow to capacity (RFC) and a specific threshold value related to assessing the acceptability (or not) of a UK junction design.

From the age, and also the age range of these documents, you can see how long the ratio of flow to capacity has been used to evaluate junction performance and acceptability in the UK. It is an established method to check the model outputs to see if RFC is at or below 0.85, or 85% if you prefer. This is known across all of the UK, and well beyond to boot. I won’t try to defend its use here, nor will I try today to persuade you to use other traffic model parameters instead – these do exist – but I also know how very attractive a ‘black and white’ answer is in a modelling world where such kinds of answers are rare indeed.

Having set the scene, let me now get to the point where I give you some really good news! Junctions 10, as many of you will know is used throughout the UK from top to bottom, to evaluate unsignalled priority junctions, and used in other countries too. You will probably also know it includes a ‘Lane Simulation’ mode, that allows many new and complex scenarios to be modelled, not possible in earlier versions that went without any form of simulation. However…

Although Lane Simulation is a great recent addition to Junctions, and a facility that we know is enjoyed by many of our users, it has a particular downside – It does not calculate RFC values for each approach in the way the core model is able to do, and hence benefit users over many years. Users of Junctions 10 would love to see this disadvantage addressed. We know this, as we have asked our users many times about this specifically and also noted similar unsolicited responses on the topic.

Anyway, after a lot of hard work by our development team, including experiencing a few false dawns along the way, I am delighted to be able to tell you that we have worked out a way to calculate RFC values in Lane Simulation mode for most scenarios. The latest release of Junctions 10 (Version 10.1) now has the ability to calculate RFCs in Simulation mode, and also calculate Degree of Saturation (DoS) values at signalled approaches in simulation mode. The release includes a few other minor improvements too. Enjoy!

No access to Junctions 10? – Please contact our team via [email protected] and ask for a trial.

Jim Binning

Product Owner

TRL Software