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Reproduced from PHOEBE website, 10 July 2023

The EU-funded ‘Predictive Approaches for Safer Urban Environment’ (PHOEBE) aims to develop an integrated, dynamic human-centred predictive safety assessment framework in urban areas. This will be achieved by bringing together the inter-disciplinary power of traffic simulation, road safety assessment, human behaviour, mode shift and induced demand modelling and new and emerging mobility data. Focused on vulnerable road users’ safety, the 3.5-year-long PHOEBE project will draw inspiration from real-world scenarios in the three pilot cities of Athens, Valencia and West Midlands. Connecting the models and methods of iRAP and Aimsun, the results of PHOEBE can be used as a blueprint by other European cities to develop their knowledge products, such as socioeconomic analysis modelling, urban road safety assessment, human behaviour and choice modelling.

PHOEBE experts have been busy at work exploring the methodological and technical approach the project will follow to develop the PHOEBE framework. They gained an overview through desk research and a literature review of latest knowledge in road safety and transport modelling. Online stakeholder surveys and focus groups were also undertaken to understand the current uses and practices of road safety assessment and microscopic simulation of traffic on urban road networks, and the extent to which they inform decision making in urban road planning and management.

The review of the state-of-the-art covered road safety assessment, traffic microsimulation, human behavioural models, modal shift and induced demand in over 300 research papers. The online survey and focus groups captured the gaps and needs of transport managers, practitioners and authorities in the three pilot cities of Athens, Valencia and West Midlands and beyond.

Summary of review findings

The findings of the state-of-the-art review brought to light the gaps in science and policy that are currently present. Additionally, the review shed light on the crucial connections between traffic simulation, road safety assessment, and the role of human behaviour models in enhancing the credibility of both; this ‘triangle’ is an important part of the basis of PHOEBE methodology. The PHOEBE framework includes several intersecting components that need to be enhanced, upgraded and interlinked to achieve the scientific objectives of the methodological framework and result in a usable and efficient policy support tool.

The review confirmed that the iRAP Star Ratings are a suitable road safety assessment methodology to meet the needs of the project. This method incorporates individual models for VRUs and is applicable across all regions and road types (including urban road networks). However, Star Ratings provide static safety ratings. Speed and flow variables from traffic simulation models will be incorporated to allow for dynamic safety prediction and a better representation of human behaviour. PHOEBE partners met recently to enhance understanding of Star Ratings among the consortium members.

Mode choice

Another behavioural aspect that is being assessed by PHOEBE is the mode choice or modal shift of users, which also has an impact on the network-level safety of a city. Understanding modal shift and induced demand is critical in understanding the changes in the network flow and speed and their impacts on safety in the transport system. Modelling the mode choice phenomenon and forecasting the Modal Share and Modal Shift is integral to modelling travel demand. It was also concluded that there is a lot of experience in developing such models for urban areas, but not for sustainable modes of transport (other than public transport), micromobility and automated mobility. The inclusion of some new modes, particularly micromobility, will be essential for the PHOEBE Framework’s capacity to forecast the uptake of new modes of transport.

Stakeholder consultations

The survey questionnaire and focus groups aimed to assess different aspects of the PHOEBE framework from the end-user perspective, to produce a Needs Statement. The survey was disseminated online with 50 participants who provided insights on behavioural models, data collection methods, modal shift data, socioeconomic models, road safety assessment and microsimulation. Nineteen (19) participants from 15 cities participated in the focus groups which followed a dedicated script and process to grasp the perceptions and experiences of their daily work, needs and capabilities while working with road safety assessment and simulation.

The Needs Statement highlights, amongst other things, that several challenges exist, including differing organisational structures related to knowledge and practice in the cities and some deficiencies in the current tools, such as the limited incorporation of modal shift options (especially with new emerging mobility solutions). Furthermore, VRUs and new mobilities need to be integrated not only into tools but also within the organisational knowledge and practice. The new emerging data sources are costly to collect and process, and the lack of human resources with relevant training and knowledge may be a barrier to exploiting these new data. The Needs Statement covers three elements of strategic goals, decision support and daily practice, as well as methodological needs.

Key messages and conclusions

Based on stakeholders’ needs and the literature review, a conceptual design of the PHOEBE methodological framework will be drafted on the basis of the following design principles (among others):

  • Mode choice and modal shift models are the first steps to be taken to simulate traffic and safety impacts
  • Fusion of road assessment and traffic simulation: the strong inter-relationship between traffic simulation and road safety assessment is at the core of the PHOEBE methodology
  • Incorporation of human behaviour models to enhance the credibility of traffic simulation and enrich the predictions of road safety outcomes

The results are just the beginning of work to be undertaken by the PHOEBE partners. They will continue exploring how the PHOEBE framework can move beyond the state-of-the-art and integrate traffic microsimulation and road safety assessment in an innovative and useful way.

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