Although the original empirical research that PICADY is based on did not explicitly consider one-way roads, it is possible to model them as follows:
1. Make sure that the turning counts are correct (e.g. if one-way in the C-A direction, there should be zero traffic travelling towards C)
2a. Junctions 8 or later: Enter the ‘Major Road Direction’ for the junction and the physical kerb-to-kerb width, and the program will then automatically carry out any conversion necessary. Do NOT double any widths.
2b. PICADY 5 ONLY: Measure the physical kerb-to-kerb width of the major road, and then double it before entering in PICADY. E.g. if the physical width of the one-way road is 4m, then enter 8m into the program. This is because the traffic model always thinks that the road is two-way, and so expects that ‘half’ of the entered width is actually available for any given movement. This is true regardless of the direction of the one-way flow.
3. If there are multiple lanes on the major road, then it may be that some of those lanes have zero effect on the junction. This would be true if, for example, a lane carries only straight-through traffic, and, due to geometry, is unavailable to traffic emerging from the minor road. In this case, you could consider removing these lanes from the model altogether.
NOTE: When modelling one-way junctions, care should always be taken to check that the results look ‘reasonable’, and (if at all possible), comparable to any similar operating junctions. The core PICADY model is calibrated only for two-way junctions.