11.2 PROJECT-LEVEL AND NETWORK-LEVEL APPROACHES

Developing network-wide assessments to guide programme development is an essential part of a comprehensive road safety programme for a road authority. This should be based on a good understanding of system-wide risks and issues. Project-level identification of risk that is consistent with the higher-level network-focused programme approach is also required. Both are discussed in Chapter 10. Assessing Potential Risks and Identifying Issues. In a similar manner, network-level approaches can be taken to address this identified risk through effective infrastructure interventions. To address system wide issues, wide scale implementation of treatments can be undertaken. This implementation can cover the network, corridor, segment or spot location for differing timeframes.

Perhaps the best documented example of this approach is the implementation of the 2+1 road design scheme in Sweden, as described in the case study below.

As well as network-level implementation of specific treatments (such as the 2+1 design identified above), frameworks can also be developed to provide guidance on the application of treatment types. As an example, a framework has been developed in New Zealand for guiding safety investment decisions based on the level of collective and/or individual crash risk. Figure 11.2 is inspired by this approach and illustrates how collective and individual risk can be used to influence cost effective outcomes. Individual risk applies to an individual road user. It is often expressed as the likelihood that a given road user will be involved in a crash (often in crashes per vehicle kilometre travelled), which takes into account traffic volume. Other metrics are also available. Individual risk is a useful measure for assessing the quality (in safety terms) of road infrastructure. Collective risk refers to the total expected crash outcome for all vehicles (e.g. crashes per kilometre) and is heavily influenced by traffic volume. Using information on collective and individual/personal risk, the treatment types can be categorised into four groups:

• Safe System transformation.
• Safer corridors.
• Safety management.
• Safety maintenance.

Roads with high traffic volumes have a high expected number of crashes; and those that include road engineering features below the standards for the function, are likely to score high in both collective and individual risk areas (the red area in Figure 11.2). Substantial investment into road safety treatments on such roads would often be justified via Safe System Transformation works, e.g. a major upgrade; provision of an alternative, higher quality route; freeway style interchanges, etc. Further examples of these higher cost, but highly effective treatments can be found in Effective Safe System Interventions in Section 11.3 Intervention Options and Selection.

Roads with intermediate collective and individual risk outcomes fall into the Safer Corridors or Safety Management categories (orange and yellow areas in Figure 11.2). For example, highways in rural areas with moderate traffic volumes, characterised by localised and scattered severe crashes and compromised road design, may fall in the Safe Corridors area. The most effective approach may be to improve the entire corridor using a mix of high-cost and low-cost solutions (e.g. installation of safety barriers, and road markings, intersection upgrades, etc.).

Safety Management ideas may apply to roads with lower traffic volumes, more scattered severe crashes (e.g. local streets and roads) and inadequate road standards. The best economic return in terms of safety would be achieved with network and/or corridor-level application of low-cost treatments, e.g. speed limit revisions, line-marking treatments, or targeted asset management (e.g. pavement resurfacing with associated safety treatments, including shoulder sealing). This group also includes roads with a high collective severe crash risk due to high traffic volumes, but with a good overall road safety standard (e.g. urban motorways). It is important to emphasise that in this case, infrastructure interventions are often not cost-effective. The most cost-effective actions may be based on targeted systemic changes, e.g. managed freeways techniques and infrastructure supported enforcement.

Roads with low collective and individual risk (green area in Figure 11.2) are most likely candidates for Safety Maintenance activities. Safety Maintenance often involves incremental and systemic changes, such as managing the road surface (and thus skid resistance), or improving signage and line-markings.

Figure 11.2 shows that as collective and individual risk increases, more extensive treatments are likely to be applicable. As the risk progresses to higher categories, the benefits of applying the lower categories treatment options should also be considered.

Although developed and implemented in a HIC, the approach outlined is equally useful in LMICs, particularly for upgrading existing road infrastructure. The approach can be an effective way to help prioritise road safety activities.

The case study from the Czech Republic provides an example of improving safety through the use of self-explaining roads.