Cluster Analysis - Understanding the French ZAAC methodology in Caen

The Importance of Prioritizing Road Safety Initiatives

Prioritization is a critical first step in developing road safety initiatives. Often, cities and regional governments lack the capacity to address entire transportation networks fully. Therefore, it is crucial to triage traffic safety projects to the areas where they will produce the most benefit—reducing speeds, eliminating collisions, and calming traffic.

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Clustering Data Points for Effective Road Safety

There are many different techniques to cluster data points in order and identify the segments of the road network where improvements are most needed. In the US, for instance, cities use the concept of the 'High Injury Network' (HIN) to narrow the focus to the 5-10% of the road network where the most serious injury crashes occur.

France uses a similar methodology to identify where interventions would yield the highest return on investment. Zones d'Accumulation d'Accidents Corporels (ZAAC) play a crucial role in identifying areas of concern and guiding proactive safety measures, particularly for the most vulnerable. These zones, also known as black spots or hot spots, are road segments with an abnormally high frequency of serious accidents.

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Addressing Road Safety Concerns in Calvados

Road safety remains a major concern for the départements, as they seek to reduce the risk of accidents and improve the safety of their users. Philémon Perrot, Director of the Calvados Prefect's Cabinet, pointed out: '[...] we can see that there are fewer accidents involving bodily injury (350 compared to 371 in 2022 and 420 in 2021), i.e., accidents are less frequent but more serious. Vulnerable people are the hardest hit: motorcyclists, cyclists, and the elderly.'

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Integrating Vianova’s Approach with Traxy Data

Vianova’s approach seamlessly integrates Traxy data (known as the Traffic Accident Analysis Bulletin, or 'BAAC file'), a comprehensive French government resource, to provide valuable information on historical collisions. BAACs play a crucial role in identifying areas of concern and guiding proactive measures to improve safety. In order to demonstrate how the functionality works while protecting the privacy of individual incidents, Vianova has developed a synthetic data set of collisions which behaves similarly to the recorded data.

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Visualizing ZAAC Zones with Heat Maps

Let's illustrate a typical example of a ZAAC zone on a heat map, showing the density of historical collisions considered serious (fatalities or hospitalized injuries) in the Caen region. For example, by zooming in on the double roundabout on the Vianova platform, we can observe 8 bodily injury accidents resulting in 7 serious casualties (fatalities in red and hospitalized injuries in orange).

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Interactive Features for Detailed Analysis

Additionally, the interactive drop-down menu allows you to view details of each collision by selecting specific points on the map. For example, a fatal scooter accident resulting in two deaths and injuries to two others could be attributed to alcohol or the area's history of being dangerous for users.

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Local authorities also have the option of displaying historical collision densities in their area on the map for an overview.

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While the accumulation of accidents can indicate the danger of a road site, it is important to note that some segments may present a high risk without having a high number of accidents. With Traxy data, users can highlight this danger through three main indicators: number of victims, collision density, and accident severity.

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For example, an accident in December 2022 involving a scooter fatality at an intersection in rainy weather can be visualized with detailed information.

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The filter function also allows users to highlight relevant elements of historical accident data according to their needs. For example, the city of Caen can filter out accidents involving alcohol and resulting in fatalities. Additionally, the city can filter by mode of transport, such as scooter accidents, or by time of day, such as accidents occurring during rush hour, along with many other elements.

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The Value of Vianova’s Platform

In conclusion, the Vianova platform is proving to be a valuable tool in the quest to reduce serious accidents, enabling the effective identification and visualization of ZAACs and the implementation of preventive measures.

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Want to Learn More?

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