6.3.1 Role in Network Operation Planning
Traffic signals are a fundamental component of network operations, and with increasing congestion and multi-modal use of the network, there is more pressure on signal operators to proactively optimise operations for the benefit of all users. A network operation plan (NOP) provides a framework for signal managers and operators to identify and implement operational treatments that will support the objectives for operation of the road network and manage conflicting modal priorities. For a detailed description of network operation planning refer to the Guide to Traffic Management Part 4 (Austroads 2016a).
Network operation planning establishes the road use priorities for particular road user groups, which can include general traffic, public transport, pedestrians, cyclists and freight. The road use priorities are based on the link and place function of the road and Figure 6.1 is an example. In this example, at the intersection of Whitehorse Rd and Nelson Rd in Melbourne, pedestrian movements have been accorded the highest priority. Cyclist, tram and bus are given the second‑level priority while general traffic and freight are provided local access only.
The assigned priorities for each road user determine the aspirational level-of-service (LOS) for the road user group. Table 6.1 shows an example of how the aspirational LOS can be set based on road use priority. It also includes descriptors of LOS developed in Austroads (2015d).
Source: VicRoads (2013c).
|Relative priority||Aspirational LOS||Description of LOS for general traffic (for congestion)|
|Strongly encourage||A||For arterial roads generally free flow-conditions with operating speeds at least 80% of the free-flow speed. Vehicles are unimpeded in manoeuvring in the traffic stream and delay at intersections is minimal.|
|Encourage||B||For arterial roads relatively unimpeded flow with operating speeds between 50–80% of the free-flow speed. Manoeuvring in the traffic stream is only slightly restricted and intersection delays are low.|
|No specific encouragement||C||For arterial roads stable operating conditions but with manoeuvring becoming more restricted and motorists experiencing appreciable tension in driving. Operating speeds are between 30–50% of the free-flow speed. At signalised intersections, vehicles generally have to stop in a queue but clear the intersection in one signal cycle.|
|Encourage local access only||D||For arterial roads small increases in traffic volumes can significantly increase delay. Operating speeds are between 20–30% of the free-flow speed. At signalised intersections, vehicles always join the back of an existing queue and take about two signal cycles to clear the intersection.|
|Local access only||D -||–|
|No priority||E||For arterial roads conditions are characterised by significant delays with operating speeds between 10–20% of the free-flow speed. At signalised intersections, vehicles take three or more signal cycles to clear the intersection.|
Source: Description of LOS for general traffic (for congestion) is based on Austroads (2015d).
In existing networks, a performance gap in network operation planning is defined as the difference between the existing LOS and the aspirational LOS weighted by the volume of the road users. Figure 6.2 is an example of a performance gap assessment of an intersection. In this example, the intersection of Whitehorse Rd and Nelson Rd is showing a significant performance gap for pedestrians. Traffic signal operation can contribute to the reduction of a performance gap by targeting improvements to specific road user groups. In the example, techniques that improve pedestrian LOS would be most appropriate.
In greenfield networks, network operation planning can also be employed to define operational strategies as part of the context sensitive design approach described in the Guide to Traffic Management Part 4 (Austroads 2016a) and the Guide to Road Design Part 2 (Austroads 2015g). Having a defined operational strategy assists in selecting and designing the most suitable traffic signal operation technique to implement.
Traffic signal techniques that are potentially appropriate for addressing road-user-specific issues are described in the following section.
Source: VicRoads (2013c).