ARRB currently undertakes research in network performance indicators and congestion cost calculation with Austroads funding. An empirical approach to the measurement and calculation of new, online performance indicators has been adopted. These indicators will make use of traffic data retrieved automatically from signal control systems and freeway management systems. The same approach was proposed for the calculation of congestion delay. Congestion delay requires a reference point for its definition and calculation. For example, the difference between the measured speed and posted speed limit is a possible and practical measure, and constitutes the congestion index in the current Austroads National Performance Indicator (NPI) Program that is based on floating-car travel time surveys. The aim of this article is to discuss what reference speeds could be used and recommends one approach for the calculation of delay using online data. This approach can be adopted nationally so a consistent method for congestion calculation is available. This article is essentially research in progress and comments on this article are therefore most welcome. (a).
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