T4-Vojnic - IRI

Vojni�, Ž., Cvijeti�, A., Kokot, D.: Nov pristop vrednotenju vzdolžnega profila novozgrajenih cestnih odsekov

New Approach for Evaluation of Longitudinal Evenness of Pavement Surfaces on Newly

Constructed Roads

Željko Vojni�, M.Sc.C.E. Asaf Cvijeti�, B.Sc.C.E.

Viadukt,d.d. Kranjceviceva 2, 10000 Zagreb, Croatia Darko Kokot, B.Sc.C.E.

Zavod za gradbeništvo Slovenije, Dimi�eva 12, Ljubljana

Abstract

This paper primarily presents information on a new approach in evaluating the longitudinal profile of pavement surfaces on the newly constructed roads, based on Index IRI and a developed methodology founded on the following design parameters:

(I) the road class, (II) the relevant values of Index IRI, (III) the criteria of the longitudinal evenness and (IV) the category of longitudinal evenness.

The road class is determined in accordance with the effective legal categorization of roads in Croatia in function of the traffic on roads expressed in AADT (Average Annual Daily Traffic)

The relevant values of the Index IRI have been defined on the basis of the processed data of the measured pavement longitudinal evenness values and on the established model of the statistical analysis. The model calculates frequencies of distribution of longitudinal profile results measured at pavement surfaces as well as the confidence of the obtained data.

On basis of the performed analysis criteria for the acceptability limit state have been determined, as well as the acceptability limit state and the limiting area (interval) of usage (fit for use) (critical area). Accordingly, proposed categorization of the longitudinal evenness values for certain road classes was produced in relation to the calculative values of the characteristic basic variables of IRI values within the defined confidence intervals.

Povzetek

V �lanku je opisan nov pristop vrednotenja vzdolžnega profila novozgrajenih cestnih odsekov. Pripravljen pristop temelji na štirih parametrih: kategoriji ceste (po hrvaški kategorizaciji glede na PLDP), relevantni vrednosti izra�unanih indeksov IRI, kriterijev za ocenjevanje vzdolžne ravnosti in kategoriji vzdolžne ravnosti cest. Relevantne vrednosti indeksov IRI so opredeljene na podlagi statisti�ne analize, s katero pridobimo frekven�no distibucijo indeksov IRI in interval zaupanja izra�unanih podatkov. Na podlagi analiz so bile opredeljene mejne vrednosti in opozorilno ter mejno obmo�je stanja. Glede na intervale zaupanja in izra�unane vrednosti karakteristi�nih spremenljivk vrednosti IRI so bile opredeljene še kategorije vzdolžne neravnosti cest.

Vojni�, Ž., Cvijeti�, A., Kokot, D.: New Approach for Evaluation of Longitudinal Evenness of Pavement Surfaces on Newly Constructed Roads

8. SLOVENSKI KONGRES O CESTAH IN PROMETU, Portorož, 25.-27. oktobra 2006 2

1 Introduction

1.1 General Evenness is an important performance

indicator of road pavement surfaces, especially as concerns the aspects of their safety and the riding comfort at the prescribed speeds. An ideal road pavement surface as envisaged by the Design practically cannot be obtained. In practice, the road pavement surfaces are usually constructed with smaller or larger discrepancies from the designed height values, resulting in the longitudinal or cross directional wave bands. The evenness of road pavement surfaces is a spatial problem. In the technical sense this problem is identified with the plane problem; most often, the longitudinal and the transverse evenness are observed individually. Unevenness of road pavement surfaces has an adverse effect over the vehicle, the driver, the passengers as well as the transported cargo, and indirectly, on the pavement structure because od the increased dynamic load. The latter directly leads to distresses of pavement structure ahead of time that was predicted. Presently there are various devices for measuring of pavement evenness all over the world, as well as various procedures (methods) of evaluating the obtained evenness [1].

1.2 Evaluating approaches for analyzing longitudinal pavement evenness

The first attempts of unifying the existing measuring methods for evaluating of the evenness of the longitudinal pavement surfaces date some twenty years ago when under the sponsorship of the World Bank an extensive investigation project was carried out in Brazil [2, 3, 4]. As a result of performed comparison of various measuring equipment, a new analising procedure for the longitudinal evenness of the pavement surfaces was expressed by the so called the IRI (International Roughness Index), calculated on the basis of the adopted mathematical model [5].

After the project in Brazil was completed, on the basis of the obtained results of measured pavement evenness, the World Bank proclaimed the IRI Index values

recommended for certain category of road, type of pavement and speed of vehicles.

In 1998, the World Road Association coordinated by PIARC, Committee C1 on Surface Characteristics conducted an international experiment to harmonize longitudinal and transverse profile and reporting procedures.

This experiment was carried out in Europe, in Japan and in the United States (EVEN project), and it enabled almost every type equipment in the world to participate [6].

The European part of this project (FILTER Experiment) was jointly conducted by some ten member laboratories of the Forum of European National Highway Research Laboratories (FEHRL) [7]. It comprised an inventory of existing methods, a theoretical study to assess the methods of analysis, and a comparative experiment with the measuring methods and different measuring equipment in European countries under actual field conditions.

The final results of the FILTER and EVEN research projects were presented in 2001 and 2002; [8, 9], and were used as a basis for harmonizing the existing European measuring methods for determination of longitudinal evenness indices, under European roads surface characteristics standardization activities.

European attempts on standardization, method harmonization, not only measuring, but also in assessing of pavement characteristics of roads as well as airfield pavements – including longitudinal unevenness of pavement – are essentially carried out within the Technical Committee CEN/TC 227 ˝Road materials˝ by the working group WG5 ˝Surface Characteristics˝.

For the purpose of unifying and harmonizing the methods of measuring the longitudinal evenness of road pavements, CEN/TC 227/WG5 has published during this year, final version of the standard draft EN 13036-5 [10], where characteristics of the road profile unevenness are expressed using also the IRI Index (International Roughness Index)

A complete computation of the IRI Index is based on a procedure recommended by the World Bank as well as on a complete computer code provided in ASTM Standards [11].



1.3 Current criteria for evaluation of longitudinal pavement evenness

The existing current criteria for evaluation of the longitudinal pavement evenness are not unique all over the world; they are based on the assumptions of certain institutions or state road authorities that prescribe different measurement procedures and methods.

It can generally be stated that in the majority of the European countries, as well as in the world, a deterministic approach is applied when assessing the longitudinal pavement evenness usually based on a simplified application of the empirical data for two limiting, accepted (fixed) values of the IRI Index, such as:

� acceptability limit value, and � allowance value.

Within such deterministic system, the interacting relations are precisely defined. The analysis of the deterministic system is generally based on the mathematic models. When assessing the longitudinal pavement evenness, expressed by the IRI Index, as per the valid Technical Specifications for Roads in Slovenia [12] and the General Technical Conditions for Roadworks in Croatia [13], the concept of such deterministic approach has also been applied.

2 Basic principles of the new approach

2.1 Initial encouragement An initial encouragement to this paper

was generated by the relevant technical information based on the specific provisions resulting from the effective technical regulations applied in Spain: PG-3, ˝Pliego de Prescripciones Técnicas Generales para obras de carreteras y puentes˝ (˝General Technical Prescriptions for road and bridge works˝), Artículo 550 [14].

In Chapter 5 (Article 550.7.3), technical regulations specify the minimal percentage of the road length (P50%, P80% and P100%) in function with the required limiting values of the IRI Index, for two road categories (motorways and higher ranked roads, and other roads).

The respective regulations have aroused an interest to start changing the perception of evaluating the longitudinal pavement profile as presently applied (deterministic approach), and that the prediction of the relevant values of the profile (as relevant basic variables) be conducted on the basis of certain statistical probability analysis.

2.2 Formulation of the Analysis Procedure – major parameters

The process of evaluating the longitudinal evenness of newly constructed road pavement surfaces expressed by IRI Index includes following major parameters:

� Road class, � Relevant values of the IRI Index, � Criteria for evaluation of longitudinal

surface evenness, and � Categories of evenness.

2.2.1 Road Class Within the proposed new model the

assessment of the road pavement longitudinal evenness, road class is treated as one of major parameters. In accordance with the legal classification of public roads in Croatia and the defined type of the traffic ranks, in function of the roads category and the traffic level on roads, expressed in AADT (Average Annual Daily Traffic) [15], the roads are divided into three classes as presented in table 1.

Table 1: Road classes in function of the road category / traffic level (AADT)

Road Class

Road Category / Traffic level (AADT)

I

� Motorways and 1st category roads (State Roads)/ AADT > 12.000 vehicles/day

II

� Roads of 2nd category (State Roads)/ AADT 7.000 – 12.000 vehicles/day

III

� Lower ranked roads of 3rd, 4th & 5th category (State, County and Local roads)/ AADT < 7.000 vehicles/day)



2.2.2 Relevant values of the IRI Index

a) Definition of particular IRI value

According to the definition, single values of the IRI Index summarize the quality of the longitudinal road profile and riding comfort and are calculated by applying the corresponding computer model [5]. Within the scope of this methodology, for single values of the IRI Index, a representative longitudinal road segment was adopted in the length of 100 meters. It was defined as IRI100.

b) Typical IRI values of characteristic basic variables

As known from the theory of probability, when processing the data on continuous random variables of the obtained data, knowledge of the basic pattern is not sufficient. An additional analysis is necessary on conformity of possible deviation. The confidence analysis makes it possible to predict the probability of occurrence of certain values of the basic variables obtained by testing.

During statistical modeling of the obtained data on testing the evenness expressed by the IRI100, the following is applied:

� Definition of empirical distribution (arranging of quality and quantity data)

� Description of distribution (shape, central tendencies, variability);

� Theoretical curve of frequencies in relation to distribution of the measured data – retrieval of the most suitable theoretical probability distribution.

By determining the acceptability limit value and fit for use interval (area), the criteria for selection of characteristic basic variables were also defined (IRIk.gr, IRId.gr. and IRIgr.up.).

While determining the characteristic basic variables of the relevant calculated IRI values during statistical processing of evaluating the measured profile, particular limiting confidence levels were recommended, as presented in table 2.

Table 2: Characteristic basic variables and recommended confidence levels

Characteristic basic variables Recommended confidence levels(g)

Symbol Definition Percentile(Pi) Quantile(pi)

IRIk.gr. Characteristic acceptability limit

value P1 = 75-85%* p1 = 15-25%

IRId.gr, Upper limit value of a confidence

interval P2 = 95% p2 = 5%

IRIgr.up Fit for use - limit value P3 = 100% p3 < p2

* Recommended limit confidence levels (P1) generally depending on road class

Note: For road class I the recommended upper confidence level is P1=85%, while for road classes II and III lower quoted confidence levels could be applied.

c) Recommended limit values of

characteristic base variables for the particular road class

The recommended limit values of the characteristic base variables for a particular road class - expressed by the IRI Index - were applied on the basis of the recent knowledge acquired when measuring the evenness of

road pavements in Croatia and Slovenia, as well as the comparative analysis and comparison of data that refer to such values obtained from the actual, relevant specifications for the motorways and highly ranked roads in various countries of the world (USA, Canada, Australia and some European countries) [16].



Table 3: Recommended limit values of certain characteristic base variables for the particular road class

Road Class

Characteristic basic variables I II III

Characteristic acceptability limit value - IRIk,,gr., [m/km] 1,50 1,80 2,25

Upper limit value of the confidence interval - IRId, gr., [m/km] 1,80 2,25 2,75

Fit for use - limit value IRIgr.up., [m/km] 2,00 2,50 3,00

d) Theoretical curve of frequencies in relation to distribution of actually measured data – retrieval of the most suitable theoretical probability distribution When analyzing the distribution of

relative frequencies of IRI100 Index on several selected, typical newly constructed road sections in Slovenia and Croatia, the exact theoretical function of distribution was attempted to be identified, optimal for approximating the histogram of relative frequencies for IRI values. The statistical data processing was done by the software ˝Statistica˝, ver. 6.1˝ (StatSoft Inc). The functional modulus Distribution Fitting was used for determination of the theoretical distribution function best suited for the distribution of the measured data and the Probability Calculator for calculation of the required IRI limit values for certain typical base variables and the required confidence levels, expressed by the values of percentile (Pi) and quantile (pi). As most suitable

theoretical curves for approximation of relative frequency histogram for the actually measured data of the longitudinal pavement evenness the following asymmetric distributions were taken into consideration: Gamma distribution (corresponding to Pearson type III distribution), Lognormal distribution, Weibull distribution, Chi-square distribution. Testing results pursuant to the Smirnov-Kolmogorov test and Chi-square test have shown that for approximation of the actually measured data, in a particular case, the Lognormal distribution is the most suitable function.

In figure 1, the following is indicated – on the assumed (typical) continuous, asymmetric theoretical distribution curve (Probability density function):

� characteristic basic variables (IRIk.gr, IRId.gr, IRIgr,up) with specified characteristic confidence intervals among such basic variables,

� categories of evenness.



Figure 1.- Typical probability density function for performed analyses, characteristic basic variables and description of typical confidence intervals

2.2.3 Criteria for evaluation of

longitudinal surface evenness

The essential criteria have to be fulfilled for particular road class of newly constructed road. Three criteria (conditions) have been established in evaluation of calculated IRI values of certain characteristic basic variables obtained on the basis of the statistical

processing of the actually measured data. The established criteria are based on comparison of the calculated IRI values with the adopted limit values for particular characteristic basic variables, in relation to the required confidence levels (table 4). The limit values adopted for certain characteristic basic variable - depending on the road class - are used pursuant to the data shown in table 3.

Table 4: Criteria for evaluation of longitudinal surface evenness

Criteria for evaluation of longitudinal surface evenness Condition Required confidence level

(Pi)

Criterion 1 IRIk,pr. < IRIk.gr P1 = 75 - 85%

Criterion 2 IRId.pr. < IRId.gr P2 = 95%

Criterion 3 IRIgr.up P3 = 100%

2.2.4 Categories of longitudinal evenness

The categories of longitudinal pavement evenness are presented for road classes in relation to the calculative values of the characteristic basic variables of IRI values within the defined confidence intervals (see figure 1 and table 5). Table 5 also shows

categorization into classes in evaluating the quality of works, based on calculated index IRI. In relation to the adopted acceptability limit values the financial penalties were quoted subject to the degree of deviation from the recommended limit IRI values. The respective model of financial penalties should be treated separately; however, this is not the subject of this paper.



Table 5: Categorization of longitudinal pavement subject to calculated IRI values of characteristic basic variables corresponding to the adopted limit values

Evenness category Condition Evaluation of measured longitudinal evenness - Financial penalties

R1 IRIk,pr. < IRIk.gr. No financial penalties

Interval/area of tolerance I

R2 IRIk.gr < IRId1,pr< IRId.gr Financial penalties due to partially

reduced quality of evenness on constructed asphalt layer

(up to 5% of the contracted asphalt layer price)

Interval/area of tolerance II

R3 IRId.gr < IRId2,pr < IRIgr,up. Financial penalties due to partially

reduced quality of evenness on constructed asphalt layer

(from 5 to 15% of the contracted asphalt layer price)

Unacceptable quality of the obtained evenness

R4 IRI.pr > IRIgr.up Corrective measures are to be undertaken depending on the

deviation from the limit

3 Verification of model proposed for evaluation of longitudinal pavement evenness

3.1 General data on analyzed motorway sections For verification of the proposed approach for evaluation of the longitudinal pavement

evenness (expressed with index IRI), a statistical analisys for selected representative sections of the newly constructed motorways in Slovenia and Croatia was performed. These are shown in table 6.

Table 6: List of selected representative segments for a statistical analysis

Analyzed segment at motorway section

Designation of motorway

Total number of analyzed IRI100 values

(traffic lane and overtaking lane)

a) Slovenia 1. Blagovica-Šentjakob A1 591 2. Vransko-Blagovica A1 348 3. Kozina-Klanec (�rni Kal) A1 289 4. Bi�-Korenitka (Trebnje) A2 193 5. Smednik-Krška Vas A2 640

Total under a): 2061 b) Croatia 1. Pirovac-Skradin-Šibenik A1 382

2. Župnja-Lipovac (Subsection: Županja-Spa�va) A3 198

3. Rijeka-Rupa A7 176 Total under b): 756



Within the statistical processing of the actually measured data, the calculated IRI values were processed and systemized into tables. Accordingly, the results are graphically presented in the form of a histogram showing distribution of the relative frequencies, as well as the distribution curve of cumulative relative frequencies. In order to perform the confidence analysis of some basic variables experimentally obtained data were approximated. The most suitable theoretical curve (probability density function) was selected by the Distribution Fitting Software (software program ˝Statistica˝).

For the majority of cases the probability density function type Lognormal distribution curve appeared to be most suitable. From the adopted Lognormal probability density function, on the basis of the confidence analysis, it was possible to foresee the probability of appearance of percentile

variable in accordance with the criteria presented in table 4.

3.2 Examples of performed analysis

As an illustration the statistical analysis of the experimentally obtained data for the two selected typical motorway sections in Slovenia and Croatia are presented. The graphical presentation of the fitted probability density function approximated to the relative distribution of the actually measured data, is shown in figures 2 and 3. In this particular case, the relevant selected representative segments on the newly constructed motorway sections are as follows:

� Smednik – Krška Vas Motorway A2: Tunnel ˝Karavanke˝ - Ljubljana – Obrežje (Slovenia)

� Skradin-Šibenik-Pirovac Motorway A1: Motorway Zagreb - Bosiljevo – Split (Croatia)

3.2.1 Motorway A2, Section: Smednik – Krška Vas

Figure 2: Graph of fitted density function to the input data (histogram of relative frequencies of

calculated IRI values) for Motorway A2, Section: Smednik-Krška Vas



� Evaluation of performed statistical analysis

On the basis of the performed, previously described statistical analysis the summarized evaluation of obtained pavement

surface evenness at the Motorway A2: Section: Smednik -Krška Vas is shown in table 7 – in accordance with the criteria quoted in table 4.

Table 7: Evaluation of obtained pavement evenness at Motorway A2: Section Smednik – Krška Vas

Required level of confidence

(Pi)

Calculated values of characteristic base variables IRIpr [m/km]

Limit values of base variables IRIgr. [m/km]

Calculated value of confidence

Pi Evaluation

85% IRIk.pr. = 1,46 IRIk.gr. = 1,50 --- Acceptable

95% IRId.pr. = 1,63 IRId.gr. = 1,80 --- Acceptable

100% --- IRIgr.up. = 2,00 P2 = 98,81 %* Unacceptable

(quantile: p3 = 1,19%)

* Calculated value of confidence for IRIgr.up.=2,0 [m/km], obtained from the diagram of cumulative relative frequencies

3.2.2 Motorway A1, Section: Skradin-Šibenik-Pirovac

Figure 3: Graph of fitted density function to the input data (histogram of relative frequencies calculated

IRI values) for Motorway A1, Section: Skradin-Pirovac-Šibenik



� Evaluation of performed statistical analysis

Evaluation of the performed statistical analysis was carried out pursuant to the same

methodology as in the previous example, and the summarized relevant results are shown in table 8.

Table 8: Evaluation of obtained pavement evenness at Motorway A1, Section: Skradin-Pirovac-Šibenik

Required level of confidence

(Pi)

Calculated values of characteristic base variables IRIpr [m/km]

Limit values of base variables IRIgr. [m/km]

Calculated value of confidence

Pi Evaluation

85% IRIk.pr. = 1,33 IRIk.gr. = 1,50 --- Acceptable

95% IRId.pr. = 1,57 IRId.gr. = 1,80 --- Acceptable

100% --- IRIgr.up. = 2,00 P = 98,40 % * Unacceptable

(quantile: p3 = 1,60 %)

3.2.3 Processing of data for

other motorway sections For the other selected representative

segments on the newly constructed motorway sections in Slovenia and Croatia (shown in table 6) the analysis of the actually measured data was performed following the same methodological approach – respecting the established criteria. Due to the limited scope of this paper, the report of the performed detailed analysis of each section could not be provided. As evident from the performed computation, all analyzed segments show confident accuracy of the established criteria what verifies the acceptability of the applied conceptual approach.

4 Conclusion This paper describes the basic postulates

and the main characteristics of the proposed new model for evaluation of longitudinal pavement evenness on newly constructed roads expressed by the IRI Index.

The subject model is founded on a semi-probabilistic concept. During the analysis procedure one of the dominant input parameters – the relevant values of longitudinal evenness (expressed as appropriate basic variables), are statistically processed and determined following the probabilistic evaluation approach. Limit values of the characteristic base variables are still determined on the basis of the adopted

(fixed) variables following the deterministic concept.

For the purpose of the most selective evaluation of the results obtained on the measured longitudinal pavement evenness, several typical confidence intervals were introduced into the analysis on the basis of which the characteristic basic variables were specified.

For evaluation of the achieved longitudinal surface evenness, three criteria have been provided based on limit values for particular characteristic basic variable.

The categories of longitudinal pavement evenness are presented for road classes in relation to the calculative values of the characteristic basic variables of the IRI values within the defined confidence intervals.

Verification of a model proposed for evaluation of the longitudinal pavement evenness – on the basis of the actually measured longitudinal evenness data at several selected representative segments of the newly constructed motorway sections in Slovenia and Croatia – confirmed the acceptability of the applied conceptual approach.

As a conclusion, it should be stressed that the applied conceptual approach, as compared to the usual evaluation procedures of measured longitudinal profile, offers better quantitative and qualitative insight into obtained evenness data in accordance with the relevant technical specifications or design requirements.



Acknowledgments This is to acknowledge the help received

from DARS d.d. (Družba za avtoceste v Republiki Sloveniji) and HAC d.o.o. (Hrvatske autoceste) regarding the provided database of results of the longitudinal pavement evenness, at particular segments of the newly constructed motorway sections in Slovenia and Croatia which served for verification of the proposed model.

Furthermore, we express our personal gratitude for useful suggestions and the relevant information concerning the subjected issues received from Mr. Bojan Leben, – ZAG (Zavod za gradbeništvo Slovenije, Slovenia).

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[16] Vojni� Ž., Cvijeti� A., Elaborate: ˝On Issues concerning Longitudinal Pavement Evenness of Newly Constructed Roads expressed by Index IRI˝ (Data collected from Internet and other sources); Zagreb, March/April 2006, (unpublished).

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T4-Vojnic - IRI