Specific signals for cyclists can be installed to provide temporal separation of cyclists from turning drivers; this will have to be considered where separated cycleways are provided. Care needs to be taken when designing exclusive cycle phases to ensure the length of time allocated is appropriate for cyclists and other intersection users. Cyclist compliance with signals is closely linked to the amount of green time they receive compared with adjacent through traffic, and safety issues are in turn linked to cyclist compliance (‘Optimisation for bicycle traffic at traffic lights’1 ). Issues are likely to arise if cyclists receive a small proportion of the green time of adjacent through traffic, and this is especially so if cyclists observe that there are few conflicting movements (ie left turners) or that pedestrians are able to cross while the cycle light is red. The photo below shows an example of this, and it results in poor signal compliance by cyclists. Conversely, providing more green time for the movements by cyclists will increase the overall intersection cycle time and decrease the level of service to other users.
There is legal ambiguity whether filter turning of drivers across a signalised cycle movement is permitted. If filter turning is not allowed for, the proportion of green time available to left turners in particular is likely to decrease, and where the left most traffic lane caters for shared left turn and through movements, this can have significant consequences on through traffic.
Further information on signal phasing and timing will be provided in the TCD Manual Part 4.
In the interim, specific cycle signals may include:
In addition, filter turning may be allowed at sites where left turning demand is low. As stated above, there is legal ambiguity about this, and there is no experience in New Zealand with how ‘low turning demand’ could be defined. This is an area where more experience needs to be gained.
To allow cyclists to ‘demand’ an all-red extension time, detection technology can be used to detect the presence of cyclists entering large intersections near the end of a phase. This allows the extension of the all-red phase to allow slower cyclists to traverse the intersection before the phases for opposing traffic commence. This treatment was trialled in Christchurch(external link) in 2001 and subsequently accepted as a suitable technique. An advantage of this technology is that no publicity is necessary, as road users do not need to know how to activate the system. The most critical part of the design is to identify a loop placement that lies in the path of cyclists but not in the path of motor vehicles (e.g. right turning vehicles should not trigger the extension time when it is not necessary).
1. Alrutz, D., Willhaus, E., Meyhofer, H., Muller, H. & Schmidt, R. 1996. Optimierung für den Radverkehr an Lichtsignalanlagen [Optimisation for bicycle traffic at traffic lights]. Beiträge zur Stadtforschung, Stadtentwicklung, Stadtplanung [Contributions to urban research, city development, and town planning]. Hanover, Germany: PGV Planungsgemeinschaft Verkehr / Hannover.