TECHBRIEF Results of Long-Term

Pavement Performance

SPS-3 Analysis: Preventive

Maintenance of Flexible

Pavements

FHWA Publication No.: FHWA-HRT-11-049

FHWA Contact: Larry Wiser, HRDI-30, (202) 493-3079, 

larry.wiser@dot.gov

This document is a technical summary of the Federal Highway 

Administration report, Impact of Design Features on Pavement 

Response and Performance in Rehabilitated Flexible and 

Rigid Pavements (FHWA-HRT-10-066).

Introduction

Rehabilitation and pavement preservation represent the 

majority of pavement construction activity in the United States. 

Preventive maintenance includes treatments that are applied 

to pavements primarily to delay development of and mitigate 

existing distresses. These treatments focus on improving pavement functional performance and prolonging pavement life, not 

on improving the structural capacity. Selecting the appropriate 

maintenance technique and treatment application timing form 

the basis of a concrete preventive maintenance practice.

Experimental Design

In addition to a nontreated control section, the Specific Pavement Study (SPS)-3 experiment included the following four 

maintenance treatment alternatives:

1. Thin hot mix asphalt overlay (typically 1 inch (25.4 mm) 

or less).

2. Slurry seal.

3. Crack seal.

4. Chip seal.

Additionally, each site was categorized according to the 

following five design factors:

1. Moisture (wet or dry climate).

2. Temperature (freeze or no-freeze zone).

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

http://www.fhwa.dot.gov/

research/tfhrc/programs/

infrastructure/pavements/ltpp/

The Long-Term Pavement Performance 

(LTPP) program is a 20-year study of inservice pavements across North America. 

Its goal is to extend the life of highway 

pavements through various designs of 

new and rehabilitated pavement structures, using different materials and under 

different loads, environments, subgrade 

soil, and maintenance practices. LTPP was 

established under the Strategic Highway 

Research Program and is now managed 

by the Federal Highway Administration.
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3. Subgrade type (fine grained or coarse 

grained).

4. Traffic loading (low or high).

5. Existing pavement condition (good, fair, 

or poor).

This experimental design resulted in 48 different 

experimental combinations of factors. In total, 

33 States and Canadian Provinces participated 

in the experiment, and 81 sites were constructed 

and monitored for the assessment.

Performance Indicator

To evaluate the effectiveness of preventive 

maintenance treatments regarding the performance of pavement sections, the alternatives 

at each site were compared to each other 

and the control section using a set of performance measures developed from LongTerm Pavement Performance (LTPP) monitoring data. Performance was evaluated as the 

deterioration measured by fatigue cracking, 

rutting, and roughness using the International 

Roughness Index (IRI). 

When selecting the performance indicator, the 

objective was to find a parameter that could 

represent the pavement performance over the 

monitoring period. The indicator also needed 

to provide a simple, stable, and comparable 

parameter that could minimize the effect of 

survey measurement errors. The selected 

indicator was the weighted average of the 

distress normalized over the monitoring period. 

The weighted average represents the total 

area under the distress versus time curve 

divided by the total time period between 

the first and last surveys. As such, it is a 

measure of pavement performance relative 

to the specific distress over the entire survey 

period, and it allows for comparisons of pavement sections monitored for different periods. 

Statistical Analysis Approach

The statistical test selected for the analysis 

was the Friedman test, which is a nonparametric test (distribution-free) for comparison 

of paired observations. Using paired observations, the performance of pavement sections 

subject to preventive maintenance treatments 

was compared to the performance of the 

control sections without the treatment as 

well as to the different treatment types. The 

Friedman test was applied to all design factors 

(moisture, temperature, subgrade type, traffic loading, and existing condition) for each 

distress type. The values used were the 

weighted average distresses normalized for 

the analysis period. The results of the test 

were used to determine whether statistically 

significant differences existed in pavement 

performance between any pair of treatments.

Analysis Results

SPS-3 pavement performance data were used 

to identify whether different climate conditions, subgrade material, traffic level, or initial 

pavement condition influences the effectiveness of a selected preventive maintenance 

treatment.

All four treatments were considered. The 

results showing preferred treatments based 

on pavement performance are presented in 

table 1 for different categories of design factors. 

The table summarizes the results of the statistical analysis for each distress type evaluated. 

Each cell represents a comparison between 

the treatments and the control section. When 

pavement performance for the treatment was 

found to be statistically significant compared 

to the control section, the treatment code 

was inserted in the cell. If no statistical 

significance was identified between the treatments and the control section, “None” was 

entered in the cell.

The overall results indicate that thin overlays 

and chip seals have superior performance,

compared to slurry seal and crack seal. In 

the majority of the cases, the latter treatments 

had performance comparable to the control 

section.

Fatigue Cracking

Chip seal and thin overlay are recommended 

treatments for freezing temperature zones, 

wet climates, and pavements with coarse 

subgrade. Under these conditions, chip seal 

performance was superior to thin overlay. If 

the pavement was initially in poor condition, 

both treatments were effective; however, thin

overlay was superior compared to chip seal.
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In no-freeze zones, dry climates, pavements 

with fine subgrade, low traffic conditions, and 

pavements initially in good condition, chip seal 

is the recommended treatment. For pavements 

in fair condition, none of the treatments were 

statistically superior to the control section.

Rutting

As shown in the table, thin overlay was an 

effective treatment option under all design 

circumstances with respect to rutting. As an 

alternative treatment, chip seal can be used in 

freeze zones and dry climatic regions.

Roughness

Thin overlay is the only treatment that was 

found to delay roughness progression. It was 

effective in freeze zones, heavy trafficked roads, 

and pavements initially in poor condition. 

Subgrade material and precipitation were not 

found to be the determinant factors. None of 

the treatments performed statistically different 

from the control section in no-freeze zones, on 

low traffic roads, or on pavements in good or 

fair conditions with respect to roughness.

Timing

One of the basic questions when planning 

preventive maintenance is when to implement 

it. Some pavements may be too deteriorated 

for effective repair and maintenance. The 

SPS-3 analysis consisted of comparing the performance of sections submitted to treatments 

at different preexisting levels of distress and 

conducting hypothesis testing to find if there 

were differences in performance. It was found 

that thin overlay can only perform better 

compared to other treatments if the IRI level 

is higher than 7.34 ft/mi (1.39 m/km). For lower 

IRI levels, the sections performed similarly, 

and there was no advantage of applying thin 

overlays.

When comparing the effect of timing on 

rutting, regardless of the level of preexisting 

rutting, thin overlays outperformed the other 

treatments, followed by chip seal. For cracking, thin overlays and chip seals outperformed 

the other treatments and the control section,

when the initial cracking was lower than 

232.13 ft2

/mi (13.4 m2/km). For higher levels 

of cracking, every treatment outperformed 

the control section, with chip seal being the 

best, followed by thin overlay.

Conclusions

Based on the analysis of LTPP SPS-3 sites, the 

following conclusions were drawn:

• Thin overlay and chip seal were more 

effective than slurry seal and crack seal 

treatments and performed better than the 

control section for fatigue cracking. 

• Thin overlay mitigated and slowed the

progression of rutting under all circumstances. There were no significant differences between slurry seal, crack seal, 

and the control with respect to rutting.

• Chip seal effectively reduced the development of rutting in no-freeze zones and 

wet regions.

• Only thin overlay was effective in mitigating and delaying the progression of

Table 1. Preferred treatments.

Distress

Preferred 

Treatment

Temperature Precipitation Subgrade Traffic Pavement Condition

Freeze

No 

Freeze Dry Wet Fine Coarse Low High Good Fair Poor

Fatigue 

cracking

1st choice CH CH CH CH CH CH CH CH CH None TH

2d choice TH — — TH — TH — TH — — CH

Rutting

1st choice TH TH TH TH TH TH TH TH TH TH TH

2d choice CH — CH — — — — — — — —

Roughness 1st choice TH None None None TH TH None TH None None TH

CH = Chip seal; TH = Thin overlay.

— Indicates that no data were available.

Note: Chip seal is not included as an option for roughness because it was never the preferred treatment method.
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Researchers—This study was performed by Applied Research Associates, Inc., Elkridge, MD.

Distribution—This TechBrief is being distributed according to a standard distribution. 

Direct distribution is being made to the Divisions and Resource Center.

Availability—This TechBrief may be obtained from FHWA Product Distribution Center by 

e-mail to report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online 

at http://www.fhwa.dot.gov/research/.

Key Words—Pavement treatment, Preventive maintenance, Pavement preservation, Chip 

seal, Slurry seal, Crack seal, Thin overlay, LTPP data, Data analysis, and SPS.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no 

liability for the use of the information contained in this document. The U.S. Government does 

not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this 

report only because they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides highquality information to serve the Government, industry, and public in a manner that promotes 

public understanding. Standards and policies are used to ensure and maximize the quality, 

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and adjusts its programs and processes to ensure continuous quality improvement.

june 2011 FHWA-HRT-11-049

HRDi-30/06-11(1.5M)E

roughness; however, it was only effective for pavements in freeze zones, under 

high traffic, or in poor condition.

• Thin overlays outperformed other treatments only when the existing level of IRI 

was higher than 7.34 ft/mi (1.39 m/km).

• For any existing level of rutting, thin 

overlays outperformed the other treatments followed by chip seals.

• Thin overlays and chip seals outperformed 

other treatments when the existing section 

had minimal cracking prior to the treatment 

and higher levels of preexisting cracking. 

All treatments were effective to some 

degree relative to the performance of the 

control section.

• Maintenance costs are a critical factor 

when deciding which mixture type to 

use. Cost analysis is an important step 

in selecting the optimum preventive 

maintenance treatment; however, this 

research only considered pavement 

performance.