Investigating the influence on safety of retrofitting Italian motorways with barriers meeting a new EU standard

ABSTRACT

Objective: A new European Union (EU) regulation for safety barriers, which is based on performance, has encouraged road agencies to perform an upgrade of old barriers, with the expectation that there will be safety benefits at the retrofitted sites. The new class of barriers was designed and installed in compliance with the 1998 (European Norm) EN 1317 standards for road restraint systems, which lays down common requirements for the testing and certification of road restraint systems in all countries of the European Committee for Standardization (CEN). Both the older and new barriers are made of steel and are installed in such a way as to avoid vehicle intrusion, but the older ones are thought to be only effective at low speeds and large angles of impact. The new standard seeks to remedy this by providing better protection at higher speeds. This article seeks to quantify the effect on the frequency of fatal and injury crashes of retrofitting motorways with barriers meeting the new standards.

Methods: The estimation of the crash modification was carried out by performing an empirical Bayes before–after analysis based on data from the A18 Messina–Catania motorway in Italy. The methodology has the great advantage to account for the regression to the mean effects. Besides, to account for time trend effects and dispersion of crash data, a modified calibration methodology of safety performance was used.

Results: This study, based on data collected on 76 km of motorway in the period 2000–2012, derived Crash Modification Factor point estimates that indicate reductions of 72% for run-off-road fatal and injury crashes and 38% in total fatal and injury crashes that could be expected by upgrading an old safety barrier by complying with new EU 1317 standards. The estimated benefit-cost ratio of 5.57 for total crashes indicates that the treatment is cost effective.

Conclusions: The magnitude of this benefit indicates that the retrofits are cost-effective even for total crashes and should continue in any European country inasmuch as the estimated Crash Modification Factors are based on treatment sites that are reasonably representative of all European motorways.

KEYWORDS:

• Road safety
• rural motorways
• lateral barriers
• median barrier
• crash modification factor
• empirical Bayes

Acknowledgments

The authors express their gratitude to the East Sicily Highway Police Department and to the Management of Sicilian motorways (CAS) for their help in obtaining the data used for the analysis.

Funding

The third author's research was supported by a discovery grant from the Natural Sciences and Engineering Council of Canada.