Cyclists have a greater effect on the circulating carriageway than on the entry. This effect was confirmed through TRL research.
This effect can be easily taken account of in Junctions 10.1 (ARCADY and PICADY)) and all newer versions, such as Junctions 11. To do this, open the “Vehicle Mix” screen, and select the “Cyclists” tab to enter your percentages of cyclists. At the bottom of this tab you can define the two different PCU factors – one for cyclists on approaches, and one for cyclists on the circulating carriageway (on roundabouts, or on any movement that is opposing other traffic (within priority intersections). The defaults of 0.2 and 0.8 are based on the TRL research into the effect.
If you are yet to subscribe to the most recent Junctions version, there is a work-around, albeit an awkward one, that will give a similar effect as follows: Firstly, when entering your O-D Matrix demand flows in PCUs, use 0.2 for cyclists and run the model. Keep hold of that file (or results) and then set the O-D flows using an assumed 0.8 PCU per cyclist. The run that uses 0.8 PCU for a cyclist should then be used, setting the site-specific intercept correction to adjust the capacity of the entries upwards to compensate for the fact that the cyclists have a 0.2 PCU effect rather than 1.0 on the entries. i.e. using the difference in capacity between the two runs. The slope of the linear capacity relationship cannot be changed in ARCADY hence why you want to use a PCU value for cyclists which is appropriate for the CIRCULATING carriageway. N.B. This should work quite well, but it should be remembered that the site-specific variation is making a FIXED difference in the entry capacities – if the geometries change the difference between the two different PCU runs may change. If significant geometric or flow changes are made the process should be repeated.
(Updated April 2025)