5.7 Integrating Data

The integration of safety data provides a large number of benefits, including:

• Effective management of safety (e.g. linking intermediate and final outcome data; see Section 5.2 Identifying Data Requirements).
• Identifying crash risk types and locations in a more comprehensive manner (e.g. through combined use of both reactive and proactive approaches, benchmarking, better information on injury outcomes, greater knowledge of crash contributors; see Chapter 10. Assessing Potential Risks & Identifying Issues).
• Better knowledge in order to identify cost-effective solutions (e.g. through better knowledge of the infrastructure that already exists; see Chapter 11. Intervention Selection and Prioritisation).

In addition, linked data can be used to validate other sources of information. As an example, crash database systems can either draw information directly from asset data to provide additional information on road elements, or this linkage can be used to reduce the likelihood that data entry errors will occur by validating the presence of different road features or assets. It can also be used for research on specific topics.

Key linkages include combining crash data with:

• Traffic data.
• Road inventory data.
• Vehicle registrations.
• Vehicle inspection data.
• Population statistics.

The linkage process involves several stages and can be temporary (e.g. for a specific project or policy need) or permanent (e.g. for ongoing analysis and monitoring). Data needs to be collected in a format to facilitate linkage. This typically involves provision of a common data element, most usefully the spatial coordinates for road based elements (including crashes), while for non-spatial data, another unique identifier will be required for the datasets to be linked. A comprehensive safety information system may have a large number of component files.

Once the data has been linked, it can be analysed through merging of data files. For spatial data, a GIS software package is able to assist greatly in this task and is particularly useful for mapping information from different sources.

Once the initial investment in collecting data has been made, it may be a relatively low-cost task to join different sources of information together to meet a variety of needs, especially if a unique identifier has been used in each dataset. In other circumstances, especially where data is not in a compatible format, the task might be quite substantial involving considerable investment.

One of the more commonly used linkages is the calculation of crash rates to allow either benchmarking or identification of high-risk locations. For example, crash data can be combined with population figures, traffic volumes, or vehicle registrations to provide a useful comparison of risk. Ideally, each of these would be presented as fatal and serious injury crash rates. Each of these measures is useful for different purposes, as outlined below:

• Crashes per 100,000 population: This measure reflects the direct impact of road crashes on a country, region or community. It provides a useful basis to compare road safety outcomes with other types of risk (e.g. risk of death from heart disease). It can also be used to identify risks for different subsets of the community (e.g. risk by age, gender, location). This is one of the most commonly used comparisons in road safety, particularly because it is easy to collect relevant data to make this calculation.
• Crashes per vehicle kilometres travelled (VKT): This measure reflects the level of safety based on the amount of travel undertaken. It can be used to compare different travel modes (such as between car, bus or train), different road types (e.g. undivided compared with divided roads) or infrastructure (e.g. roundabouts compared with traffic signals). This requires good knowledge of traffic volumes and distances travelled, and this information is often difficult to collect.
• Crashes per 10,000 registered vehicles: This measure is often used as a proxy for the amount of travel, as it is much easier to collect than kilometres travelled. It can be useful for analysis of performance at a national level but has limited applicability for more detailed analysis.

Crash data can also be combined with road inventory data. At a simple level, this can provide information about current road features that may be present, providing information about possible infrastructure safety improvements. For example, crash data of run-off-road crashes could be presented alongside information on current roadside barrier locations on a map to allow for a quick visual analysis of locations that might benefit from further barrier installation.

Combining data on crashes with roadway, asset, environment, and traffic volume data can lead to some important outcomes relating to safety performance of infrastructure. It is possible to compare the safety performance of different types of infrastructure for different traffic volumes. For example, the performance of divided and undivided roads can be compared for different traffic volumes. In addition, crash performance of different infrastructure can be compared at different levels of traffic volume, for different road user types, or for different environment types (e.g. low versus high-speed environments). Box 5.9 provides information on the US Highway Safety Information System.

BOX 5.9: US HIGHWAY SAFETY INFORMATION SYSTEM

Recent initiatives in integration have involved the combination of crash data and road risk assessment data. This provides a very powerful tool for identifying risk locations and possible solutions. Further information on the combination of this data can be found in Section 10.5. Combining Crash Data and Road Data and Chapter 11. Intervention Selection and Prioritisation.

The Denmark case study shows how data can be integrated to create a more accurate picture of contributing factors to crashes.