9. Performance Indicators
National performance indicators for network operations on arterial roads and freeways have been proposed by Austroads (Austroads 2007e). They are summarised in Table 9.1.
|Performance measurement area||Performance measure||Comments|
|Traveller efficiency||Travel speed||This indicator monitors congestion in terms of speeds. It is derived from spot speeds on freeways measured directly using point sensors such as a pair of loops. On arterial roads, it can be derived from the inverse of travel times estimated from an ATC system.|
|Variation from posted speed||This indicator monitors the proportions of a road network at various levels of deviation from posted speed limits on freeway or arterial road links.|
|Arterial intersection performance||This indicator monitors the proportion of an arterial road network at various levels of unusual or extreme congestion.|
|Lane occupancy||This indicator monitors the average number of persons per lane per hour during a specified period on a representative sample of arterial roads and freeways.|
|Vehicle occupancy||This indicator monitors the average vehicle occupancy (persons/vehicle) on a representative sample of arterial roads and freeways, and is also an input to the calculation of the lane occupancy measure.|
|Reliability||Travel speed variability||This indicator measures the variability of speeds by calculating the coefficient of variation. It is displayed as the proportions of a road network at different levels of variability in a measurement time period.|
|Speed and flow||This indicator is based on the product of speed and flow. A high productivity is achieved if both speed and flow are maintained near maximum values (i.e. near free-flow speed and capacity flow).|
Source: Austroads (2007e).
The formulation of these indicators is such that, while being primarily aimed at reporting the performance of a whole arterial network, the inputs are gathered at a link or segment level and the indicators are therefore candidates for performance measures for the aggregate effect of traffic operations at scales ranging from individual links to whole networks. The national indicators have also been chosen and formulated so that, with the exception of the vehicle-occupancy and lane‑occupancy measures, the underlying data can be automatically acquired from traffic control systems. Further detail on their formulation can be found in Part 4 of the Guide to Traffic Management (Austroads 2016a).
The values reported for these performance indicators reflect the aggregate outcomes of a range of traffic operations activities along with the effects of changes to the road infrastructure. The individual contributions of each traffic operations activity will not necessarily be evident in them; separate performance indicators for each major traffic operations function are required for this.
For further reading on performance measures and measurement tools for freeways and arterial roads, refer to Austroads (2007e and 2007h).