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Proactive safety assessment of urban through-roads based on GPS data

Ambros Jiří, Elgner Jan, Valentova Veronika, Bąk Radosław, Kieć Mariusz

Archives of Transport

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2024

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Vol. 69, iss. 1

113--125

EN

Road safety is a worldwide issue, while urban roads account for a high share of serious road injuries, especially involving vulnerable road users, such as pedestrians or cyclists. Specifically, the safety of major roads through built up areas (through-roads) is insufficient due to mixed traffic conditions including vulnerable road users, varying driving behaviour, and many disruptions, which are combined with excessive speed. In this context, various traffic calming measures have been implemented to improve road safety, such as gateways or pedestrian refuge islands. However, the specific safety impacts of traffic calming combined with specific characteristics of through-roads are often unknown, since most traditional evaluations have been limited by small sample sizes of crash data, as well as wide variations in physical and road characteristics. To overcome the limitations of crash-based evaluations, we used the GPS-based data from a sample of 21 Czech and 12 Polish through-roads to develop the Speed-Safety Index, which combines speed, speed variance, and traffic volume. Our study has three novelty features: (1) To assess safety, we used speed and speed variance simultaneously. (2) To complete the missing link between specific traffic calming measures and safety, we validated the statistical relationship between the developed Speed-Safety Index and crash history. (3) To prove the usefulness of the developed index, we also showed its practical interpretation by proving the effect of spacing between traffic calming measures on safety. The index proved to be well correlated to crash frequency and it also proved the effect of spacing between traffic calming measures: the longer spacing, the smaller speed-reducing effect. The paper concludes with a discussion on the limitations, which we plan to address in further research, by moving from the current macro-perspective (Speed-Safety Index on the level of through-roads) to the micro-perspective (focusing on individual directions, locations, and traffic calming measures). We also plan to investigate the method’s applicability in different contexts. If the approach proves feasible, with reliable and valid results, it may become an alternative for a proactive network-wide road assessment, as called for by the European Road Infrastructure Safety Management Directive.

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Analysis of Covid restrictions’ influence on road traffic crashes and related road users’ behaviour in the Czech Republic

Bucsuházy Kateřina, Zůvala Robert, Ambros Jiří

Archives of Transport

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2023

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Vol. 66, iss. 2

109--121

EN

The Covid pandemic and following restrictions worldwide influence various aspects -lockdown does not only have economic consequences but is also associated with a change in population mobility. As well as the spread of a pandemic and the associated numbers of infections and deaths, policy responses and restrictions have also varied from country to country. Despite all the negative impacts of the Covid pandemic, the decrease in crash-related injuries may be seen as one of the positive impacts of lockdown politics. The change in crash characteristics during the Covid lockdown may provide new insights and help design countermeasures for road safety improvement. It is not sufficient to generalize findings across individual countries, there were different trends in crash frequency and severity during the Covid lockdown The main purpose of this study was to investigate the Covid restriction's impact on road safety in the Czech Republic. The retrospective analysis was performed using data the Police crash statistics. In addition to data from the main Covid periods (2020 and 5 months of 2021 data), crash data from 2016-2019 as the period unaffected by the Covid pandemic, were used as a control group. The study focused not only on the overall crash frequency but also on the analysis of the crash frequency according to the individual crash participants. Crash data did not indicate significant changes in risky behaviour. The mobility decrease was associated with decreased crash frequency, especially of vehicles and pedestrians. The crash numbers also reflect changes in how people spend time, respectively an increase in leisure time activities in some age groups and a change in usage of transport modes. Two-wheeled vehicle users (cyclists, motorcyclists) crash frequency was more influenced by seasonality. While the crash frequency of vehicles (personal vehicles and HGVs) and pedestrians was better correlated with mobility data, the cyclists and motorcyclists crash frequency were better correlated with temperature.

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Analysis of safety impact of paved shoulder width on Czech secondary roads

Ambros Jiří, Křivánková Zuzana, Zůvala Robert, Bucsuházy Kateřina, Frič Jindřich

Archives of Transport

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2021

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Vol. 60, iss. 4

125--136

EN

Traffic safety is influenced, among other factors, by characteristics of the roads, which include the width of the shoulder. Shoulder width was noted to have a large effect on crash frequency, as well as on traffic speed. In this paper, we focused on paved shoulders. Previous studies confirmed that increasing the width of the paved shoulder is associated with a decrease in crash frequency. However, wider shoulders may encourage higher driving speed, which is related to an increase of impact speed and crash severity – this issue was hypothesized, but not statistically investigated. Thus, conclusions based on crashes and speeds contradict each other, and there is no simple answer to the question of the safety impact of wide shoulders. To address this gap, we analyzed a sample of two most typical categories of Czech secondary roads, which differ only in the paved shoulder width (S9.5 roads with 0.75m-wide shoulder, and S11.5 roads with 1.75m-wide shoulder) and thus present a suitable example for studying the safety impact of paved shoulder width. We used generalized linear models of crash frequency, and multinomial logistic models of crash severity (separately for single-vehicle and multi-vehicle crashes), as well as a statistical test of differences in speed for the two road categories. The results showed that: Firstly, there were fewer crashes on S11.5 roads compared to S9.5 roads; this was true for both single-vehicle and multi-vehicle crashes. Secondly, single-vehicle crashes on S11.5 roads were more severe compared to S9.5 roads; the change of severity in multi-vehicle crashes was not statistically significant. Thirdly, driving speeds on S11.5 roads were approx. by 7 km/h higher compared to S9.5 roads. These findings support the hypothesis of an association between wider shoulders, higher speeds, and increased crash severity, especially in the case of single-vehicle crashes. As a practical solution, various speed management measures, including widening to a 2+1 road, may be recommended.

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Where and when do drivers speed? A feasibility study of using probe vehicle data for speeding analysis

Ambros Jiří, Elgner Jan, Turek Richard, Valentova Veronika

Archives of Transport

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2020

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Vol. 53, iss. 1

103--113

EN

Speed is a critical transportation concept – it is one of the most important factors that road users consider in relation to route convenience and efficiency; at the same time speed has been recognized as the most influential risk factor. To improve speeding analyses, an emerging data source – probe vehicle data (also known as floating car data), may be used. This data enables obtaining information on vehicle speeds, without being limited in time and space. To prove the feasibility of using this data, a study was conducted on a sample of Prague expressway and collector roads. Firstly, probe data sample validity was checked through comparison to a traditional speed measurement technique – average speed control. Secondly, descriptive analysis of speeding was performed, focusing on speeding differences across homogeneous road segments in individual hour intervals. Thirdly, statistical models were also developed to explain which road parameters contribute to speeding. Analysis utilized cross-section and geometry parameters, which may potentially be related to speed choice and driving speed and speeding. In general, the applied concept proved as feasible: particularly night time was found more prone to speeding, and the rates were significantly different between segments. Statistical models indicated the statistically significant influence on speeding: lower speed limit, lower number of lanes, absence of roadside activities, or presence of horizontal curves. Information on these factors may be generalized and used for planning adequate speeding countermeasures. Final discussion also identified and described several challenges for future research, including free-flow speed estimation uncertainty, quality of speed-safety models, and potential multicollinearity of explanatory variables.

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Proactive assessment of road curve safety using floating car data: An exploratory study

Ambros Jiří, Altmann Jarosław, Jurewicz Chris, Chevalier Anna

Archives of Transport

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2019

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Vol. 50, iss. 2

7--15

EN

Driving speed is an important risk factor, especially when negotiating horizontal curves. Therefore it may be useful in extracting surrogate measures to proactively safety assessment, a practice consistent with a current shift towards a Safe System approach to addressing road trauma. Review of previous literature indicated two categories of studies: (1) studies focusing on a safe driving perspective, i.e. studies primarily interested in finding the cut-off point in FCD data characteristics between safe and unsafe driving; (2) studies focusing on relating meaningful risk rates (percentages of exceeding the risk thresholds) to specific locations, and thus identify safety critical sites. However, no study was found that specifically focused on the relationship between kinematic characteristics (other than just speed) and road curves. The presented study focused on exploring the relationship between acceleration and jerk thresholds and crashes occurring on road curves. The first objective was to determine meaningful acceleration and jerk thresholds to utilize in explaining safety performance when negotiating curves. For this purpose floating car data (FCD) from a fleet of company vehicles, driving in rural sections of national roads in the Czech Republic, was collected and used to derive and validate potential surrogate safety measures. FCD presents in-vehicle information with several benefits compared to traditional techniques, such as feasibility of data collection, relatively unlimited spatial coverage, and availability of historical data. In the analysis, lateral acceleration and longitudinal jerk were found to be the most influential measures of curve safety performance. To sum up, the exploratory study outlined a practical approach to proactive evaluation of road curve safety: FCD data can generate useful surrogate measures of curve safety (acceleration and jerks) associated with crash history. A larger study is required to strengthen robustness of the results and provide confidence necessary for practical application. Potential use cases may include conducting interim evaluations of curve road safety treatments, or in-vehicle monitoring devices for detection of potentially unsafe manoeuvers and providing real-time feedback to drivers based on a combination of identified safety thresholds.