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Simulation and modelling

The road network of the Province of Arezzo runs through a hilly landscape. To reduce accidents the local authority integrated road safety work in the strategic planning process

and found it in new technologies. For its strategic traffic planning, the Province of Arezzo uses PTV Visum software. “The idea was to bring together the planning in PTV Visum and the accident data from the SIRSS project, and to evaluate the aspect of road safety even during the planning process”, says Vadi. This was possible thanks to a new module in PTV Visum, PTV Visum Safety. In addition, the Province of Arezzo used speed data from TomTom to get a deeper under- standing of the accident situation and causes by providing real-world behav- ioural data about estimated speed limit observance rates and speeding risks at black spots. “The use of traffic planning software

as an analytical tool for road safety rather than as an isolated tool offers advantages when it comes to data con- sistency”, says Michele Giuliani of TPS srl, which assisted with the case study in the Province of Arezzo. “The transport model includes data about the traffic vol- ume as well as structural data. Both can be used as additional information and be incorporated into the analysis without additional data handling”. In addition, thanks to PTV Visum Safety, the road safety data can be imported very easily into the transport model. “Without hav- ing to worry about an additional data source or another system, for example, the traffic planner can analyse the black spots in PTV Visum and assess them according to different accident types

Europe/Rest of the World Vol 8 No 2

– both in strategic as well as in operative planning”, explains Giuliani.

FROM THE FIRST OVERVIEW TO BLACK SPOT MANAGEMENT In the first step of its analysis, the Province of Arezzo got an initial overview of the data: With the Safety module in PTV Visum, so-called heat maps show where the critical points in the road network are. Places with an especially high accident rate (more than 20 accidents within 50 metres) are displayed in red. Using differ- ent filters and parameters, this view can be differentiated further and set accord- ing to specific accident categories. In order to find the black spots for the

region under examination, the Province of Arezzo used a multi-step approach: “First, the use of a bigger buffer size of 100 metres was used to catch whole complex intersections such as big roundabouts“, explain Vadi and Giuliani. After creating these first black spots at sites with more than 10 accidents within that area, the remaining accidents were analysed for additional black spots generation using an iterative process with a decreasing capture buffer size and number of acci- dents”. As a result of the procedure above, a list of the top 100 black spots was cre- ated for Black Spot Management (BSM) purposes. During the process of identifying

critical black spots, one intersection named SR71 km 130+085 (Castiglion Fiorentino/Via del Palazzuolo) was

singled out for further in-depth analy- sis. Contributing factors to the accidents were assessed in order to find the poten- tial causes. The main accident type was ‘frontal collision’ and ‘frontal-lateral col- lision’ within the intersection regulated by fixed signal control. “The result of our analysis was that

the main cause of accidents recorded in this intersection was the disregarding of the priority rules for conflicting turns”, explains Vadi. “Our primary resolution approach has been to change the signals in the intersection from three stages to four. We expect that the separation of the conflicting turns will lower the acci- dent rate”. Both the current and the new scenario have been simulated in PTV Vissim on a microscopic level in order to verify their feasibility and avoid creating potential congestion. And how would the Province of Arezzo

sum up the case study? “There is a real benefit to improve road safety work and strategic and operational transport plan- ning within only one system”, says Vadi. “With this new approach we hope we will be able to significantly shorten the time from an accident situation arising to mit- igation efforts on the road.”

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 Sonja Koesling is Corporate Communications Manager at PTV

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© iStockphoto/Michal Krakowiak

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