Traffic management

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8.1.3 Hierarchy of Sub-systems

Historically, separate stand-alone systems have been developed for motorway traffic management, i.e. separate VMS, VSL, travel time, ramp metering etc. However, the sub-systems within the smart motorway system are integrated to the extent that management and interaction is essential. Even though the hierarchy of sub-systems may change according to the circumstances, the sub-systems are still inter-dependent in the way they operate. Without integration the operators would be faced with a significant challenge due to the complexity of the interaction required, particularly during an incident.

The hierarchy of sub-systems during default (normal) operation is shown in Figure 8.1. Default operation occurs when there are no incidents and the system is safely optimising throughput and travel speed.

Figure 8.1: Hierarchy of sub-systems under default (normal) traffic conditions

Source: ARRB Group (2012a).

During an incident, the lane use management system (LUMS) becomes the dominant sub-system to control lane use and speed limits as shown in the hierarchy (Figure 8.2).

Figure 8.2: Hierarchy of sub-systems during an incident

Source: ARRB Group (2012a).

In either mode of operation, the management system provides automated operation that works within pre-defined rules, generally with minimal operator input unless override is necessary.