Road infrastructure safety assessment using the integrated method - case study DN2.

This study aims to practically test, identify vulnerabilities and analyses the limits of working tools for assessing road network safety and validate the integrated method proposed by the European Commission in the context of different technical classes of national roads in Romania. The research aims to adapt, convert, and transform the calculation values of the formulas of the proactive evaluation tool to the values used by national norms for road design and construction. 2 evaluation parameters are analysed, which represent the width of the traffic lane, respectively the widths and type of shoulders. On the other hand, the study is a tool for analysing road infrastructure safety, for efficiently allocating resources and for prioritising specific road safety inspections on the most dangerous sections of roads. The case study is the comparison of the results obtained from the safety assessment of DN 2 road infrastructure, both by the proposed test method and by the method adopted by the European Commission following Member States’ comments.


Introduction
In accordance with paragraph 5, Article 5 of Directive (EU) 2019/1936 [1] amending Directive 2008/96/EC [2], The European Commission has made available to Member States a tool and a guide containing "guidelines on the methodology for conducting systematic road safety assessments and network-wide safety ratings" -pdf file [3].
Romania transposed the provisions of Directive (EU) 2019/1936 into national legislation by amending Law no.265/2008, republished, on traffic safety management on road infrastructure [4], with the provisions of GO 3/2022 [5].In line with the strands of action set out in Directive (EU) 2019/1936 -also called the "RISM Directive" -Member States will complete the first road infrastructure safety assessment, at motorway and national road network level, by the end of 2024.
In the first phase of the implementation process of the methodology, Romania and the other Member States finalised pilot programmes for the evaluation of a section of national road.Following Member States' comments, the European Commission amended the working tools -Excel smart files -and published on the European Union's website the adopted working version.One of the objectives of the research is the comparative analysis of the results obtained between the evaluation method used to test the evaluation methodology and the evaluation method adopted by the European Commission.The influence of removing a parameter from the proactive assessment tool, the parameter referring to "lighting", is also analysed.
Two tools are used for evaluation, one for proactive evaluation and another for reactive evaluation.With the proactive tool, NWA-p, the built-in safety of the road is determined according to its configuration and the geometric characteristics of the road infrastructure -Excel file No.1, [3].With 2 reactive instrument, NWA-r, the level of reactive safety of road infrastructure is determined according to the annual daily average of motor vehicles -AADT and the number of serious accidents resulting in fatalities / serious injuries -Excel file No. 2, [3].
The integrated road infrastructure safety assessment methodology consists of combining the results of the assessments obtained with the two assessment tools -NWA-r and NWA-p.Through the graphic integration scheme, by colour, the road infrastructure safety classification for each road segment is obtained according to a scale on 5 risk levels.
The research focuses on studying the influences of 2 of the 9 evaluation parameters of the proactive tool.For these parameters, solutions are identified to modify the ranges of values used to achieve some correspondence with the provisions of road construction standards in Romania [6].These values are used to identify correlations between road cross-sectional characteristics and impact modification factors (CMFs).These correlations are then used in calculation formulas in Excel files to ensure that the results obtained are assimilable to those available on the specialized site [7].
The research centres on conducting a comparative analysis of outcomes derived from employing two road infrastructure safety assessment methods, encompassing a total length of 472.230 km along DN 2. Additionally, the study will investigate the influence of excluding the "Lighting" parameter on road safety classification results within a 132 km segment, stretching from km 10 to km 142 on the same road.This choice was decided by the fact that DN 2 ranks first in the ranking of the most dangerous roads in Romania and registered the highest number of deaths in road accidents between 2017 and 2020, being known as the "road of death".It is analyzed comparatively the result of the evaluation by adapting the two calculation parameters to the standards of Romanian roads.
The data used in the research comes from three sources.The official results of the safety assessment of the infrastructure of the national road DN 2 are obtained from the Romanian Road Authority-A.R.R.For the values of the annual daily average of vehicles (AADT) on national roads in Romania, the database of the Center for Road Technical Studies and Informatics -CESTRIN is used, which is found on the institution's website [8].For data on serious road accidents resulting in deaths and serious injuries, the database of the Romanian Police is used [9].Table 1Table 1 presents the ranking of the most dangerous national roads in Romania in terms of road safety because of the consequences of serious accidents between 2017 and 2020.
Table 1.The consequences of serious accidents and the classification of national roads.

Proactive road infrastructure assessment method (NWA-p)
Proactive road assessment uses a tool in the form of an Excel file No. 1 [3] which contains spreadsheets and calculation formulas.Each assessed road segment is allocated a spreadsheet containing several analysis parameters targeting the built-in safety of road infrastructure, as follows: 1 -lane width, 2 -size of roadside road risk depending on distance to obstacle (RHR)/ obstacle type/slope size, 3 -curve radius, 4 -density of access points to properties, 5 -number and configuration of intersections, 6 -conflicts between pedestrians / cyclists and motorized traffic, 7 -type and width of the shoulder, 8 -presence of additional crossing lanes, 9 -presence and quality of signs and markings, 10 -lighting.The latter was used only in the test version of the integrated assessment methodology.The Excel file includes for each parameter a calculation formula or algorithm that evaluates the impact on the safety of the analysed road segment.Based on the data entered in the spreadsheet, the proactive tool provides a specific value for the accident change factor (CMF) associated with each parameter [7].The crash reduction factor (RF) is then automatically calculated by the Excel tool using the formula in equation ( 1): RF is a positive number and always less than or equal to 1.For each segment assessed, the product of the reduction factors, expressed as a percentage, represents the 'estimated road risk level score'.On national roads, depending on the value of the score obtained, the following colour coding is allocated:  between 0 and less than 50, corresponds to a "High Risk" road, red colour,  between 50 and less than 80, corresponds to an "Intermediate Risk" road, yellow colour,  between 80 -100, corresponds to a "Low Risk" road, green colour, pdf file, [3].

Analysis of proactive assessment tool parameters
Analysis of the structure, the proactive assessment tool, shows that 2 parameters are not adapted for the evaluation of roads in Romania.The values used in the calculation formulas for assessing the safety of the road infrastructure, in terms of the average width of all traffic lanes as well as the widths of the consolidated/unconsolidated roadsides, do not reflect the approach and requirements of the Romanian norms for the design and construction of roads.

Parameter
No. 1 -"lane width".For undivided roads, equation (2) provides the formula for calculating the crash modification factor (CMF) associated with parameter no. 1.The value written in cell E6 of the proactive tool is taken by the formula and the CMF is calculated, which is displayed in cell M6.Equation (3) provides the formula for calculating the CMF associated with parameter no.
Considering the recommendations set out in the report "Crash Modification Factors in Practice" [10] and the absence of consistent data in the CMFs database [7], approximate values like those incorporated in the formulas of the proactive tool of European Commission, are chosen, as there are no significant differences in bandwidths.
For proactive evaluation, depending on parameter no.2.1.2.Parameter No. 7 -"type of shoulders" and "shoulders width".CMF value for parameter No. 7 is displayed in cell M22 of the proactive instrument according to the choice of shoulder type (consolidated OR unconsolidated) and the width of the shoulder.For undivided roads, the assessment is made simultaneously in both directions of travel, and for divided roads, the assessment is made separately in each direction.
The approach of assessment by choosing a single type of shoulder is not applicable for the assessment of national roads or European national roads which, in Romania, are designed and constructed with two types of shoulder, consolidated shoulder AND unconsolidated shoulder.On the other hand, the proactive tool uses values of the widths of the shoulders that do not correspond to the values of the Romanian standards.
The types of shoulder and the values of shoulder widths for national and European national roads are set out in "ANNEX NO. 1 -Widths of platforms and roadways in alignments" from the Annex to UNWTO no.1296/2017 [6].
For parameter No. 7, the proactive instrument allowed only one type of verge to be selected.This selection is modified and currently the proactive Excel file allows the assessment to be carried out for each type of verge and on each direction of travel.
The Table 3 shows the standardised values for the widths of the two types of roadsides, both for divided and undivided roads.10.For this purpose, the results of the evaluation of a 132 km segment of the DN 2 road are compared with the test variant of the proactive tool and the results obtained with the variant of the instrument from which parameter no. 2 was removed.10.The results of the assessment of the DN 2 road by testing the variant of the methodology were presented at the EAEC MVT Congress in 2022 [11].
The results presented in Table 4 show in percentage terms how the results of the proactive assessment of the 132 km segment of the DN 2 national road are influenced due to the elimination of the infrastructure safety assessment based on the influence of parameter no.10.Thus, for split road segments, initially assessed as "High Risk", the changes are insignificant.For undivided road segments, it is found that 6.29%, representing 8.3km, changed the risk classification from "Intermediate Risk" to "Low Risk" and 1.74%, representing 2.6 km, changed the classification from "High Risk" to "Intermediate Risk".Table 4. Influence of " lighting" parameter on proactiv assessment status.and yellow to green are set at 80 and 50 respectively.To identify road segments where scores may be affected by multiplying by the mean value of parameter reduction factor no. 10 (0.954), two numeric filters are applied, with limits from 50 to 52.41 and from 80 to 83.856 on the proactive score column.

NWA -proactivă
To get a detailed insight into the impact of removing parameter no. 10, the study investigated the results of the evaluation using the integrated method, which consists of combining the results of proactive and reactive assessment.The data presented in Table 5 show that the influences are insignificant and do not manifest themselves around interest for carrying out specific road safety inspection procedures.There are no changes in the statistical data of the road segments classified "Very High Priority" and "High Priority".

Results of road assessment by proactive method
The results obtained the proactive assessment of DN 2 road, using both the initial testing method and the current method approved by the European Commission, are presented in Table 6.Comparing the results shows that the removal of parameter 10 from the evaluation led to a 1.86% change in the statistical distribution of segment lengths across road risk classes.

Reactive Road Safety Assessment Method (NWA-r)
To apply the reactive assessment method, the DN2 road was divided into homogeneous segments with approximately the same criteria as for the pro-active assessment: physical separation of directions, terrain landform, changes in road configuration (number of lanes, segments in alignment/curve), changes in values for daily average vehicles (AADT), traffic regime (urban/extra-urban).If in the proactive assessment the recommended length of road segments was 2 km, in the reactive assessment the recommended length of road segments can reach up to 7 km in the case of undivided roads and up to 15 km in the case of split roads -pdf file [3].
Of the three approaches to reactive assessment proposed by the European Commission, for the evaluation of DN 2 road, the formation of road segments that include alignments and intersections was chosen as a working method.Each of the road segments is evaluated according to the number of serious accidents occurring on them and the AADT value allocated.Depending on the data entered in the calculation tables of the reagent instrument, the level of associated road risk is determined.

Statistical data of reactive evaluation
The reactive tool is presented on the specialized site in the Excel file No. 2, (3).In the "Preliminary info" sheet, for the family of national roads, data taken from official sources were entered.The total length of national roads is 17,913 km, value taken from the Excel file "TEMPO TRN 139A" [12].For the average daily average value of vehicles (AADT), corresponding to the family of national roads, the value of 8,000 vehicles/ 24 hours is used [8].Between 2017 and 2020, 10,316 serious deaths and injuries were registered on national roads.The data come from the database of the Romanian Police -Road Department [9].

Results of DN 2 road evaluation by reactive method
In the Excel spreadsheet, "1.Methodology (S)" the lengths of road segments resulting from the subdivision of DN 2 based on the specific criteria of the method are entered.For each segment, serious accidents are allocated.The average daily traffic (AADT) value recorded on the road section to which the evaluated segment belongs is considered.
The test variant of the reactive method, using the calculation formulas of the reactive instrument calculates the parameters of each segment: "Accident density" and "Accident rate".Based on the accident density thresholds and accident rate thresholds, two classifications are obtained for each section, "accident density classification" and "accident rate classification".final ranking, according to the test variant approach, is determined considering the more critical classification between the two rankings.The final class to which each section belongs is obtained."Low risk", "High risk" or "Unsure".
The official working method, agreed by the European Commission, uses the Poisson method.Using the Poisson method, upper and lower thresholds are defined for the observed number of accidents on each section (and junction).These thresholds are then converted into accident density thresholds and accident rate thresholds for each section.For the final ranking of the section is recommended to rely on the comparison of the accident rate if they are available.Otherwise, the ranking is based on the comparison of accident density.(processing after "Deliverable D.4.2 -Network-wide safety assessment tool and guidance" document version no.14, November 2022, European Commission) The results obtained from the reactive assessment of the DN 2 road, using both the initial test method and the agreed working method, presented in Table 7.The reactive evaluation through the two working variants reveals significant differences.There is a notable 24.5% decrease in road segments classified as High Risk.The data also indicate that the uncertainty zone in road risk assessment has increased from 32.61% to 60.85%.

Integrated method of road infrastructure safety assessment (NWA-I)
The method consists of graphically combining the results of proactive assessment and reactive assessment based on a color scheme and results in the classification of road segments into 5 risk classes, according to Table 8 -Class 1 (Dark green), Class 2 (Green), Class 3 (Yellow), Class 4 (Orange), Class 5 (Red).Data on the statistics of segments classified as Class 5 shall be used by the competent authority for planning specific road safety inspections.The data show that the results of the classification of road infrastructure by risk classes are significantly influenced by the change in the working method for reactive assessment.

Conclusions
The study makes significant contributions to the implementation of the road infrastructure safety assessment procedure in Romania.It supports the competent authority in streamlining the planning and monitoring of road safety inspections, as well as in the training of specialized personnel responsible for carrying out the procedures outlined in the RISM Directive.
Following the two working methods of the European Commission, the research conducts a comparative analysis between the results obtained from proactive evaluation and reactive evaluation on the national road, which is the most dangerous in terms of road fatalities, DN 2.
The research findings to the adjustment of the parameters of the proactive evaluation tool, and the analysis provides insights into the correlation between the widths of traffic lanes and road shoulders with the estimated CMF values for various technical classes, in accordance with Romanian standards for road design and construction.
Considering that the results of the reactive evaluation significantly impact the outcome of the integrated road network safety classification, it is crucial to pay increased attention when identifying segments based on areas with a high concentration of severe accidents.

Table 2
1, of roads in Romania belonging to different technical classes, incorporate the appropriate values from Table 2 into the corresponding calculation formulas of the proactive Excel file, according to the equations presented below.supplies information on the correlation between lane widths and estimated CMF values for various lane widths, categorized by technical classes, following Romanian standards for road design and construction.

Table 2 .
CMF values for lane widths depending on the technical class of the road.

Table 3 .
Data for the "Lookup Table" sheet and CMFs values for road shoulder types.The research aims to find out to what extent the results of proactive evaluation are influenced by removing parameter no.
For parameter No. 10, which is the average of the reduction factors for all road segments, expressed as a percentage, recorded a value of 95.4%.This indicates that the final proactive safety score can be influenced by approximately 4.6% for each road segment.It has been established that each score, obtained through the product of reduction factors, corresponds to a specific colour indicating a certain level of risk.The thresholds for switching from red to yellow

Table 5 .
Influence of " lighting" parameter on integrated assessment status.

Table 6 .
Results of proactive assessment using two working methods (NWA-P).

Table 8 .
Results of the safety assessment of DN 2 road infrastructure by the integrated method.