The traffic flows in my PICADY output file do not add up – the total demand from Arm C is not the same as the input for that arm – the total entering on this arm is smaller than it should be, and the proportion turning right is higher than I’ve specified. Can this be right?
The flows DO add up. The confusion comes from the way the flows are labelled. The flows associated with streams C-AB and C-A are added together to give the total. C-A is NOT a subset of the flow on C-AB. Traffic arriving on arm C and leaving on arm A is split between the two streams. A proportion of this straight-ahead traffic gets blocked by right-tuning traffic on the main carriageway and ends up in the CAB stream while some gets through unimpeded and this remaining flow is in the C-A traffic flow – i.e. the flow is ‘mutually exclusive’. The C-A traffic stream you will notice has no queue and no delay associated with it as it goes through the junction uninterrupted.