Identification of Hazard Location and Ranking of Measures to Improve Safety on Local Rural Roads

PROJECT SYNTHESIS
1. INTRODUCTION
Road safety evaluations on two-lane rural roads with low/medium traffic flows can raise concerns both due to the general deficiency of reliable data on road accidents and to the circumstance that few crash data due to low traffic, not always can give enough information on accidents distribution and causes.
Based on these considerations, the project "Identification of Hazard Locations and Ranking of Measures to Improve Safety on Local Rural Roads" (Italian acronym IASP), funded by the European Commission (DG TREN) and the Province of Catania (Italy), aims to define a methodological approach purposely designed for the safety evaluation of two-lane local rural highways. The proposed model uses both procedures referring to the geometric design consistency of road alignment and to the Safety Inspection process of road features.
The IASP methodology integrates the results of design consistency models with those deriving from the safety issues evaluation made during Safety Inspection processes.
A Safety Index (SI) is formulated by combining three components of risk: the exposure of road users to road hazards, the probability of becoming involved in a accident and the resulting consequences should an accident occur.
The SI model was verified comparing the ranking of risk carried out by the model with the actual number of accident on the same road sections.
The research activity was concluded monitoring of the safety benefits of road interventions. In particular, the following monitoring methodologies were applied:

1. Before-After Accident Analyses.
2. Monitoring of vehicle spot speed.
3. Monitoring of vehicle trajectory and speed profile.
In Figure 1 it is shown the Flow-chart of the methodological approach of IASP project.

Figure 1 - Flow-chart of the methodological approach proposed in the IASP project.

2. SAFETY INDEX
The proposed approach makes use of theoretical-experimental models for the evaluation of design consistency which has been demonstrated effective in identifying hazardous road locations due to geometric road alignment. However, the resulting analyses, although effective in addressing alignment inconsistencies, do not highlight all the potential accident contributory factors.
Therefore, Road Safety Inspections (RSI) are aimed at identifying potential hazards, which are assessed by measuring risk in relation to those road features that may lead to future accidents, so that remedial treatments may be implemented before accidents happen. In order to use safety inspections as part of a quantitative safety evaluation process, the IASP project defines new procedures and criteria for identifying and ranking safety issues. The ranking criteria take into account the road safety effects of the identified issues.
Using the collected information, based on the data obtained from the RSI combined with information from theoretical-experimental models of design consistency, it was possible to define a Safety Index value (SI) able to measure the level of risk in different homogenous stretches of road, according to the model:

S.I. = Vulnerability x Exposure x Magnitude

Where:
Vulnerability = probability of accident defined basing on the integrated system of Safety Inspection + design consistency models;
Exposure = million vehicles per kilometer;
Magnitude = possible consequences of the accident referring to speeds and roadside hazard.

The SI has two main applications. High-risk segments, where safety measures that can reduce accident frequency and/or severity already exist, can be identified and ranked. Specific safety issues, that give more contribution to unsafety, are pointed out in order to give indications regarding more appropriate mass-action programs.

2.1. Case Study
The proposed methodology was tested on about 100 km of provincial roads in order to propose a suitable model for the safety evaluation of local two lane rural roads.
On this sample, a mobile laboratory has been used to collect useful data for the horizontal and vertical road alignment reconstruction, as well as other fundamental information as section width, road markings, pavement conditions and accident data were collected directly from Traffic Police and Carabinieri reports.
Safety Inspections were carried out by a team of ispectors trained in the use of the IASP procedure.
The same sample of two lane local rural roads was used in order to perform both the IASP Accident Prediction Model and The IASP Geographic Information System.

2.2. Validation
Validation of the procedure was carried out by a comparison of the risk rank obtained using the SI and accident history. The SI was assessed in 30 segments chosen from the sample of two-lane rural highways in Italy and the actual accident situation was obtained with the EB procedure.
Spearman's rank-correlation was used to determine the level of agreement between the rankings obtained using the two techniques. The results from the Spearman's rank-correlation analysis validate the SI, indicating that the ranking from the SI scores and the EB estimates agree at the 99.9% level of significance with a correlation coefficient equal to 0.8.
Moreover, in order to test the reliability of the Safety Inspection methodology, the agreement of the results of the general safety issues ranks produced by different groups of inspectors has been addressed. Specifically, with the aim of checking the consistency of the risk assignment between different inspectors, the statistic kappa has been used. On the whole, the reliability of the procedure is satisfactory, especially if it is considered that the identification of the safety issues is a very complex task based on human evaluations and expertise not supported by instrumental measures.

3. INTERVENTION AND MONITORING
Monitoring of the safety benefits of road interventions was carried out. In particular, the following analyses were performed:
1. Improvement interventions on a road stretch. Monitoring by means of Before-After Accident Analyses.
2. Enforcement interventions to reduce traffic speed. Monitoring by means of Before-After Speed Analyses.
3. Improvement interventions on a curve. Monitoring by means of Before-After Vehicle Trajectory and Speed Analyses.
Before-and-After studies were chosen in order to evaluate the effectiveness of an intervention comparing the conditions observed before and after the carrying out of the works.
In order to evaluate whether the differences between the evaluation parameters (number of accidents that would have been expected, mean speed values and trajectories) obtained from the before and after surveys were significant, statistics tests were used.

REFERENCES
[1] S. Cafiso, G. La Cava, A. Montella, M. Pernetti "A Methodological Approach for the Safety Evaluation of Two-Lane Rural Roads with Low-Medium Traffic Volume" 1st European Road Congress, 24-26 November, Lisbon, Portugal, 2004.
[2] S. Cafiso, G. La Cava, S. Leonardi, G. Pappalardo, A. Montella "Operative Procedures for Road Safety Inspections" 13th International Conference Road Safety on Four Continents, 5-7 Ottobre 2005, Warsaw, Polland.
[3] Cafiso, S., G. La Cava, A. Montella, and G. Pappalardo "A Procedure to Improve Safety Inspections Effectiveness and Reliability on Rural Two-Lane Highways." The Baltic Journal of Road and Bridge Engineering, Volume 1, No.3, 2006, pp. 143-150, ISSN 1822-427X.
[4] S. Cafiso, G. La Cava, A. Montella "Safety Index for Evaluation of Two-Lane Rural Highways". Transportation Research Record n. 2019, Washington, D.C., 2007.
[5] Cafiso, G. La Cava, A. Montella "Safety Evaluation Process For Two-Lane Rural Highways" 4th International SIIV Congress, 12-14 September 2007, Palermo Italy.
[6] Cafiso, G. La Cava, A. Montella "Safety Assessment For Two Lane Rural Local Roads - EU-IASP Project" 23rd PIARC World Road Congress, Paris France 2007
[7] S. Cafiso, G. La Cava, A. Montella, Final Research Report "Identification of Hazard Location and Ranking of Measures to Improve Safety on Local Rural Roads: I.A.S.P.)" in http://ec.europa.eu/transport/roadsafety/publications/projectfiles/iasp_en.htm
[8] Cafiso, G. La Cava, A. Montella, G. Pappalardo "Manuale per le ispezioni di sicurezza extraurbane secondarie e locali" (ITA) - "Operative procedures for safety inspections of two-lane rural roads (EN)". ARACNE editore. (Esempio di analisi di sicurezza, ITA)