Safety reviews of existing roads aim to identify any features which may lead to future crashes, so that remedial treatments may be implemented before crashes happen. Safety reviews are complementary and not alternative to accident investigation studies. Accident investigation is a “reactive programme”, it examines past accidents and aims to remove or change the features that contributed to those past crashes. Safety review is a “proactive programme”, aimed at reducing road accidents before they occur. Accident investigation tend to concentrate on single locations, whereas safety reviews are more akin to mass action studies. Safety reviews may be high cost-effective, but the subjective nature of the process may give rise to inconsistencies which limit their effectiveness. To address this issue, a technique to support road safety reviews in order to quantify the safety gains that could be achieved by addressing the problems identified in the review process is presented. The approach is based on known accident relationships, and a systematic process has been described to determine which road features should be investigated and how each feature should be evaluated during the review. As a result of the process, a potential for safety improvement index (PFI) is calculated. The validity of the PFI has been evaluated by comparing the results of the PFI index, which has been assessed in 400 kms of rural two lane highways, with expected collision frequency. Collision frequency has been determined by applying a collision prediction model, calibrated in the study network, and has been refined by applying the Empirical Bayes technique. Correlation between EB safety estimates and PFI values is highly significant, with 93% of the variation in the estimated number of accidents explained by the PFI value. The level of agreement between the results of the EB estimates and the PFI has been evaluated also by the Spearman’s rank-correlation coefficient. Sites were ranked according to both the EB estimate and PFI, with the results of the Spearman correlation indicating agreement at a 99.9% significance level. Due to the validation and quantifiable nature of the PFI, the procedure can be used to support road safety reviews, accident investigation, and decision-making. High risk segments, where safety measures that can reduce accident frequency and/or severity do exist, and specific safety issues, which contribute to unsafety, can be identified. The procedure can be helpful also to support the safety reviews carried out on low volume roads, where often accurate accident data do not exist.

Potential for Safety Improvement of Existing Roads

MONTELLA, ALFONSO
2004

Abstract

Safety reviews of existing roads aim to identify any features which may lead to future crashes, so that remedial treatments may be implemented before crashes happen. Safety reviews are complementary and not alternative to accident investigation studies. Accident investigation is a “reactive programme”, it examines past accidents and aims to remove or change the features that contributed to those past crashes. Safety review is a “proactive programme”, aimed at reducing road accidents before they occur. Accident investigation tend to concentrate on single locations, whereas safety reviews are more akin to mass action studies. Safety reviews may be high cost-effective, but the subjective nature of the process may give rise to inconsistencies which limit their effectiveness. To address this issue, a technique to support road safety reviews in order to quantify the safety gains that could be achieved by addressing the problems identified in the review process is presented. The approach is based on known accident relationships, and a systematic process has been described to determine which road features should be investigated and how each feature should be evaluated during the review. As a result of the process, a potential for safety improvement index (PFI) is calculated. The validity of the PFI has been evaluated by comparing the results of the PFI index, which has been assessed in 400 kms of rural two lane highways, with expected collision frequency. Collision frequency has been determined by applying a collision prediction model, calibrated in the study network, and has been refined by applying the Empirical Bayes technique. Correlation between EB safety estimates and PFI values is highly significant, with 93% of the variation in the estimated number of accidents explained by the PFI value. The level of agreement between the results of the EB estimates and the PFI has been evaluated also by the Spearman’s rank-correlation coefficient. Sites were ranked according to both the EB estimate and PFI, with the results of the Spearman correlation indicating agreement at a 99.9% significance level. Due to the validation and quantifiable nature of the PFI, the procedure can be used to support road safety reviews, accident investigation, and decision-making. High risk segments, where safety measures that can reduce accident frequency and/or severity do exist, and specific safety issues, which contribute to unsafety, can be identified. The procedure can be helpful also to support the safety reviews carried out on low volume roads, where often accurate accident data do not exist.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/8781
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact