Banned traffic movements – will they affect my PICADY results?

Generally if the banned movement is one that is NOT a controlling flow – e.g. a left turn from a minor road (B-C) – then the fact that it is banned can be modelled by simply specifying that the movement has zero demand.

However if the banned movement is one that another movement would ordinarily give way to, then this WILL affect the results. Traffic giving way to a movement with no traffic on it is not the same as banning that movement. Drivers have to check that they can proceed and that entails an element of delay which is a component of the queueing delay that PICADY calculates (and also part of geometric delay). This checking delay is absent if an otherwise controlling movement is banned. For instance, if your junction is such that the C-B movement is not allowed, and this is clearly indicated (or implied by the layout), then traffic leaving the minor arm will not need to check to see if there is any approaching C-B traffic. As mentioned, this is not the same as simply have zero demand on the C-B stream. It may, however, be a matter of judgement as to whether the banned movement is obvious to the controlled traffic, or whether drivers still check that the road is clear in the same way that they would do at a normal junction.

In any case, you cannot specify this situation in PICADY. The good news though is that, because this effect is not taken account of, your PICADY results will be slightly pessimistic rather than optimistic.