From the TfL guidance:
7 Cyclist Considerations
7.1 Introduction
The number of cyclists in London is growing, especially during peak periods, and on significant cycle commuter routes often exceed 10% of total vehicle flow*. A growth in cycling is integral to the Mayor’s vision for London so it is important to consider the role and impact of cyclists upon the network. The magnitude of impact is normally a function of the number of cyclists as a percentage of total traffic.
The traffic modeller should consider carefully the effect of a proposed scheme on cycling (and any growth in cycle demand) before selecting the best software for the modelling exercise.
7.2 Junction Design
Schemes are advantageous to cycling if they help cyclists to maintain a steady speed and a direct course without interruption or obstruction from a position where they can be seen by drivers and pedestrians. For this reason the cyclist user experience can benefit from specialist provisions within a scheme. Cycle safety may be improved through the use of Advanced Stop Lines (ASLs), widened carriageways or dedicated cycle-lanes. In schemes where specialist provisions are proposed it is important to model the impact that these will have on all road users including public transport.
ASL’s allow cyclists to position themselves at the front of queuing traffic where they are able remove themselves from conflict with general traffic. Where a scheme predicts a large number of cyclists an ASL can be assessed by traffic modelling. Consideration should be given to providing cycle feeder lanes to ASLs which allow easy access and safer cyclist progression within the carriageway.
Further guidance on cycle design can be found in Chapter 4 of the London Cycling Design Standards*.
7.3 Inclusion of Cyclists
The volume of cyclists has a direct impact on the ability of traffic models to accurately represent their influence on network performance. As volume increases, their impact on general traffic behaviour generates issues that can require detailed assessment.
Where the volume of cyclists exceeds approximately 20% of the traffic volume on any one approach they may have a disproportional effect on modelling results and their influence may need further attention. For this reason it is encouraged to ensure classified traffic surveys explicitly include cyclists.
Micro-simulation traffic modelling software is often capable of modelling basic cyclist behaviour. Care should be taken to ensure any model accurately represents both cyclist speed and vehicle overtaking behaviour. Where an engineer uses deterministic traffic modelling software the modeller can only reflect the aggregate impact of cyclists by directly modifying parameters which influence junction performance.
* - London Cycling Design Standards – A guide to the design of a better cycling environment, London Cycling Centre of Excellence, Transport for London, 2005.
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