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Network Bridge Deck Surface Friction Testing: Issues and Performance Evaluation 1

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Shuo Li, Ph.D., PE, Research Engineer 5

Division of Research and Development 6

Indiana Department of Transportation 7

West Lafayette, IN 47906 8

Tel: (765) 4631521 9

Email: sli@indot.in.gov 10

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Guangyuan Zhao, Graduate Research Assistant 12

Department of Building Construction Management 13

Purdue University 14

West Lafayette, IN 47907 15

Tel: 765-494-5602 16

Email: zhao179@purdue.edu 17

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Junlin Liang, Ph.D., Visiting Scholar 19

Department of Building Construction Management 20

Purdue University 21

West Lafayette, IN 47907 22

Tel: 765-494-5602 23

Email: liang130@purdue.edu 24

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And 26

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Yi Jiang, Ph.D., .P.E., Professor 28

Department of Building Construction Management 29

Purdue University 30

West Lafayette, IN 47907 31

Tel: 765-494-5602 32

Email: jiang2@purdue.edu 33

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Submitted on July 31, 2014 to TRB 94th

Annual Meeting 37

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Word count: 5261 (3511 words + 4 tables + 3 figures) 41

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ABSTRACT 45

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Bridges play a significant role in providing safe and efficient roadway transportation. Friction 47

performance on bridge decks is believed to be critical due to potential early freezing of 48

precipitation on the deck surface and because accidents on bridges, in a confined space, may 49

create more significant mobility issues. In addition, bridge deck friction is becoming one of the 50

key factors in bridge deck preventative maintenance. As a result, the friction performance of 51

bridge decks is becoming an increasing concern. The Indiana Department of Transportation 52

(INDOT) formally started annual inventory bridge deck friction testing at the network level in 53

2013, which has resulted in additional efforts to enhance travel safety. This paper presents the 54

test procedures utilized by INDOT to undertake annual inventory friction testing for bridge decks 55

at the network level. In particular, this paper addresses the critical issues associated with friction 56

testing on bridge decks, including test reliability, accuracy, and network performance evaluation. 57

It was concluded that a single friction test in accordance with ASTM E274 is capable of 58

providing a reliable test result to accurately characterize the deck surface friction performance 59

for a typical bridge. In addition, it was found that bridge decks on interstates tend to have more 60

friction issues than those on conventional roads such as US highways and State routes. 61

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INTRODUCTION 90

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The Indiana Department of Transportation (INDOT) conducts annual network inventory 92

pavement friction testing every year to ensure public travel safety, particularly to reduce wet 93

pavement skidding crashes. Also, the friction test results have been used by INDOT pavement 94

engineers to assess candidates for pavement resurfacing and preservation treatments. However, 95

like other state transportation departments, the INDOT network pavement friction inventory test 96

program was initially established to cover roadway mainline pavements. Some critical locations, 97

including bridge decks and interchange ramp pavements, might have been overlooked in the past 98

due to the limitations of technologies and resources. In 2008, as an initiative to address potential 99

concerns over ramp pavement friction performance, the INDOT Division of Research and 100

Development (R&D) conducted friction testing on a total of 42 selected interstate ramps that 101

account for approximately 13% of total interchange of ramps in Indiana. It was found that for 102

these tested interchange ramps, the 15th

percentile friction number was 29 that was measured 103

with the standard smooth tire at 40 mph. This was extended to indicates that overall, the 104

interchange ramp pavements in Indiana were in good friction conditions and capable of 105

providing sufficient skid-resistance in wet weather (1). 106

However, it was not until recently that INDOT started annual inventory friction testing on 107

bridge decks at the network level. No other state transportation agencies have been reported to 108

conduct annual inventory bridge deck friction testing so far. It is well known that most state 109

transportation agencies have been conducting annual inventory pavement friction testing using a 110

locked trailer in accordance with the ASTM Standard E274-97, Standard Test Method for Skid 111

Resistance of Paved Surfaces Using a Full-Scale Tire (2). This method is intended to evaluate 112

pavement test sections of uniform age and uniform composition subjected essentially to uniform 113

tire pressure and does not specifically address the friction measurement of bridge decks. In 114

addition, the calculation of friction or skid number is made in lights of the horizontal and vertical 115

forces recorded over a time interval of 1.0 to 3.0 s (typically 1.5 s for INDOT’s friction test 116

trailers). In other words, the test section should be on average 90 to 150 feet (30 to 45 meters) 117

long for friction testing, depending on the test speed. This makes it difficult for the operator to 118

judge if a bridge is long enough to conduct the test while travelling at a test speed that typically 119

varies between 30 and 50 mph (48 and 80 km/h). 120

Bridges play a significant role in providing safe and efficient roadway transportation. 121

Friction numbers on bridge decks are believed to be critical due to potential early freezing of 122

precipitation on the bridge deck surface and because accidents on bridges, in a confined space, 123

may create significant mobility issues. In addition, bridge deck friction is becoming one of the 124

key factors in bridge preventative maintenance, particularly bridge deck surface treatment. As a 125

result, the frictional performance of bridge decks is becoming an increasing concern. The 126

INDOT Division of Research and Development conducted field trials to evaluate the feasibility 127

of annual inventory bridge deck friction testing in 2012. Due to the success of test trials, the 128

INDOT formally started annual inventory bridge deck testing in 2013. All bridge deck locations 129

with friction numbers equal to or lower than 25 were reported to the corresponding districts for 130

necessary actions. This paper presents the test procedures utilized by INDOT to undertake annual 131

inventory friction testing for bridge decks at the network level. To the authors’ knowledge, this 132

kind of information may be very useful for other state transportation departments that are 133

interested in providing seamless friction information to cover not only mainline pavements, but 134

bridge decks as well. 135

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RELIABILITY OF A SINGLE TEST 137

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The ASTM E274-97 standard test method requires a total of at least five tests at intervals not 139

greater than 0.5 mile (1 km) in length to evaluate the frictional properties of a test section. 140

However, this does not work for inventory bridge deck friction testing at the network level due to 141

two main reasons. First, as pointed out earlier, the INDOT friction test trailers typically calculate 142

the friction number in lights of the average vertical and horizontal forces over a time period of 143

1.5 s. When friction testing is undertaken at the standard test speed of 40 mph (60 km/h), the 144

bridge should be at least 88 feet (27 m) long to ensure a successful test. Therefore, a total of five 145

tests may require a test section of at least 440 feet (135 m) long. This implies that friction testing 146

can only be conducted on some long-span bridges. However, a large number of bridges in 147

Indiana are short- and medium-span bridges. Second, if five tests are conducted in the same 148

segment, it will be very time consuming to make U-turns to repeat the test, particularly when the 149

exit or entrance is located far away from the bridge. In reality, friction testing with an ASTM 150

E274-97 locked wheel trailer is different from other pavement non-destructive (NDT) testing 151

such as the falling weight deflectometer (FWD) test. For example, one FWD test may only 152

indicate the strength of a localized pavement structure. Nevertheless, a friction number taken at 153

40 mph (60 km/h) is the average frictional property for a segment of 88 feet (27 m) long. For 154

medium- and even long-span bridges, a segment of 88 feet (27 m) long may provide a result 155

representative of the entire bridge. 156

To examine if a single test can provide a reliable friction result, the authors conducted a 157

field verification test at a bridge in Lafayette, Indiana. This bridge is located on SR-25 next to 158

the interchange of I-65 and SR-25, which makes it very easy to make U-turns to repeat testing 159

rapidly. In addition, this bridge is a two-lane concrete bridge with concrete deck. During the 160

verification test, friction numbers were measured in two scenarios. In Scenario I, only two test 161

runs were conducted in the northbound. However, the second test was conducted after the 162

previous test so that the deck surface was dried out. In Scenario II, a total of six test runs were 163

conducted over the same deck segment in the southbound. The time interval between two 164

consecutive tests was very short so that the deck surface was still wet due to the water applied in 165

the previous test. It should also be pointed out that the deck surface was treated in 2010 to restore 166

friction performance. The treatment was made by applying one layer of binder, and then one 167

layer of sands onto the deck. The average friction number was 82 after installation. However, 168

field visual inspection in 2012 revealed that most of the sands in the wheel path were lost due to 169

the tire wearing action. Seemingly, this type of treatment may not provide a durable friction 170

surface for bridge decks. 171

Presented in Table 1 are the detailed results from the verification test using a standard 172

smooth tire (3), including test time, air temperature, test speed, vertical force, horizontal force, 173

and friction number. According to ASTM E274, the friction number is calculated as follows: 174

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100W

FFN ×= (1) 176

where FN = friction or skid number; 177

F = horizontal force applied at the tire-pavement contact interface; and 178

W = vertical force on the locked test wheel. 179

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TABLE 1 Results of Reliability Verification Test 181

Scenario Test Run Test Time Air Temp.

(oF)

Vert. Force

(lbs)

Hor. Force

(lbs) FN

I 1st 9:59 74 1058 244 23.1

2nd

10:21 75 1046 249 23.8

II 1st 10:01 75 1043 253 24.2

2nd

10:04 75 1044 238 22.8

3rd

10:08 75 1050 225 21.5

4th

10:11 75 1053 211 20.0

5th

10:14 75 1065 204 19.1

6th

10:18 75 1039 207 19.9

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Eq. 1 is established with respect to the classic Coulomb’s friction law. However, care 183

should be taken to measure both F and W when friction testing is conducted on the curves or 184

grades. It is shown that in Scenario I, the friction number taken in the second test is very close to 185

that in the first test. This is because that the second test was conducted roughly 22 minutes after 186

the first test, and the deck surface wetted in the first test was completely dried out. In Scenario II, 187

however, the first test produced the greatest friction number, and the fourth test produced the 188

least friction number, which is mainly due to the effect of water applied during testing. Because 189

the subsequent test was conducted shortly (less than 4 minutes) after the previous test, the water 190

applied in the previous test remained on the surface, resulting in a thicker water film in the 191

subsequent test. In reality, this is illustrated by the vertical and horizontal force measurements. 192

For these five tests, the variations between the vertical forces were all less than 11.5%, except for 193

the fifth test, in which, the vertical force was 2.4% greater than that in the forth test. However, 194

the horizontal forces exhibited a decreasing trend of around -5%, which continued until the fifth 195

test. The horizontal force in the sixth test was slightly greater than that in the fifth test. This 196

indicates that the effect of remained water became negligible in the sixth test. Overall, the 197

friction number taken in the first test in the southbound is very close to those in the northbound. 198

It can be concluded that a single test is capable of providing a friction number that is reliable for 199

inventory bridge deck friction test at the network level. 200

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ACCURACY OF A SINGLE TEST 202

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INDOT inventory friction test program requires that the low friction numbers together with their 204

locations should be reported to districts for necessary actions. Therefore, the accuracy of test 205

result, particularly low friction numbers, is of great importance for decision making. A great 206

effort has been made by INDOT to enhance the repeatability and reproducibility of the network 207

pavement inventory friction test (4). To validate the accuracy of a single test result, surface 208

texture testing was conducted on a bridge with concrete deck on I-90. In reality, the purpose of 209

the texture test was two-fold. First, during the bridge deck test trials at the network level, this 210

bridge exhibited poor friction performance. Therefore, the texture test was conducted to verify 211

the surface friction so as to provide the detailed information at the project level. Second, it was 212

intended by the authors to convince the bridge engineers the accuracy of the inventory bridge 213

deck friction test at the network level. It is well known that the surface texture test produces the 214

mean profile depth (5) used to characterize the surface macro-texture that has been proven to be 215

the dominant factor affecting surface frictional properties216

this paper, the mean profile depth 217

information on this laser scanner can be found elsewhere 218

utilized in each test to cover a nominal 219

Presented in Table 2 are the 220

(FN) was measured on July 9, 2012221

measured on September 27, 2012. 222

MPD is 0.172 mm. It has been reported 223

pavement friction (7). To the authors’ knowledge, this is probably due mainly to the lack of 224

information on the surface micro225

However, a general rule of thumb is that FN decreases as MPD decreases. 226

when a pavement surface exhibits 227

smooth tire (8), its surface MPD is typi228

that while the bridge deck exhibited good integrity, the deck surface in the wheel path 229

middle lane had experienced medium polishing as shown in Figure 230

concluded that a single test is capable of producing 231

friction performance. In reality, 232

Figure 2 shows the 3-D graphs of the macro233

micro-texture varies differently from the macro234

micro-textures. Since the laser scanner is only capable of capturing the micro235

wavelength ranging between 0.03 mm and 0.5 mm, the author236

remarks. 237

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TABLE 2 Bridge Deck Surface Friction and Texture Test Results239

Type of Test

Surface Friction 07/09/2012

Surface Texture 09/27/2012

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FIGURE 1 Photo of the bridge deck for texture scan testing242

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the dominant factor affecting surface frictional properties at high speed and in wet weather

ofile depth measurements were made using a laser scanner. The detailed

information on this laser scanner can be found elsewhere (6). In this paper, ten scan lines were

nominal scan area of 100 mm long and 75 mm wide.

the surface friction and texture test results. The friction number

(FN) was measured on July 9, 2012, and the surface texture mean profile depth (MPD) was

measured on September 27, 2012. It is shown that the measured FN is 22.7 and the

has been reported that the macro-texture is a poor predictor

. To the authors’ knowledge, this is probably due mainly to the lack of

information on the surface micro-texture, particularly when pavement surface is very smooth.

a general rule of thumb is that FN decreases as MPD decreases. It was indicated

exhibits a friction number of around 20 measured at 40 mph

its surface MPD is typically less than 0.25 mm. Also, visual inspection revealed

bridge deck exhibited good integrity, the deck surface in the wheel path

had experienced medium polishing as shown in Figure 1. Therefore, it can be

a single test is capable of producing accurate test result on the deck surface

friction performance. In reality, the authors did examine both the macro- and micro

D graphs of the macro-texture and micro-texture scans. Apparen

texture varies differently from the macro-texture, which decides the roles of macro

. Since the laser scanner is only capable of capturing the micro

wavelength ranging between 0.03 mm and 0.5 mm, the authors are hesitant to make conclusive

2 Bridge Deck Surface Friction and Texture Test Results

Test Date Test Parameter Average of Results

07/09/2012 FN 22.7

09/27/2012 MPD 0.172 mm

hoto of the bridge deck for texture scan testing

and in wet weather. In

using a laser scanner. The detailed

ten scan lines were

00 mm long and 75 mm wide.

The friction number

mean profile depth (MPD) was

It is shown that the measured FN is 22.7 and the measured

texture is a poor predictor of overall

. To the authors’ knowledge, this is probably due mainly to the lack of

avement surface is very smooth.

t was indicated that

at 40 mph with a

visual inspection revealed

bridge deck exhibited good integrity, the deck surface in the wheel path in the

Therefore, it can be

on the deck surface

and micro-textures.

. Apparently, the

, which decides the roles of macro- and

. Since the laser scanner is only capable of capturing the micro-textures with a

s are hesitant to make conclusive

2 Bridge Deck Surface Friction and Texture Test Results

Average of Results

hoto of the bridge deck for texture scan testing

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(a) Macro-texture 244

FIGURE 2 3-D graphs of the macro245

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NETWORK BRIDGE DECK FRICTION PERFOR247

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There are about 6066 bridges on the 249

medium- and long-span bridges. A bridge is defined as a structure having an opening of more 250

than 20 feet (9). However, the classifications of short251

on the type of bridges and superstructure252

bridges in three different categories. 253

than 88 feet, which are not long enough for a single 254

having a deck length of 88 to 150 feet, which are long enough for 255

bridges in Category III are those bridges 256

one or more tests may be conducted for th257

and bridge conditions. It should be pointed that the 258

purpose of this task. In reality, field friction testing may be conducted at variable speeds. 259

Therefore, the required length for a single test change260

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TABLE 3 Number262

Bridge Category

I

II

III

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As mentioned earlier, INDOT starte264

2013. A total of 1225 bridges were successfully tested, including 970 bridges on interstates, 12265

bridges on US highways, and 130 bridges on State routes, which ac266

of all bridges and 30% of the bridges in categories II and III. During field testing, the typical test 267

speeds utilized by INDOT are 30 mph, 40 mph, and 50 mph. The target test speed is 40 mph to 268

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texture (b) Micro-texture

D graphs of the macro- and micro-textures generated by the laser scanner

DECK FRICTION PERFORMANCE

on the public roads under INDOT’s jurisdiction, including short

span bridges. A bridge is defined as a structure having an opening of more

However, the classifications of short-, medium, and long-span bridges depends

e of bridges and superstructure materials. Presented in Table 2 are the numbers of

bridges in three different categories. Category I consists of bridges having a deck length of

not long enough for a single friction test. Category II includes bridges

of 88 to 150 feet, which are long enough for a single friction

bridges in Category III are those bridges having a deck length of more than 150 feet. Apparently,

one or more tests may be conducted for the bridges in category III, which depends on the traffic

It should be pointed that the above categories are defined

task. In reality, field friction testing may be conducted at variable speeds.

length for a single test changes from speed to speed.

Numbers of Bridges under Different Categories

Bridge Category Deck Length (feet) Number

< 88 1971

88 to 150 1346

> 150 2749

As mentioned earlier, INDOT started network bridge deck inventory friction testing in

bridges were successfully tested, including 970 bridges on interstates, 12

bridges on US highways, and 130 bridges on State routes, which account for approximately 20%

the bridges in categories II and III. During field testing, the typical test

speeds utilized by INDOT are 30 mph, 40 mph, and 50 mph. The target test speed is 40 mph to

s generated by the laser scanner

, including short-,

span bridges. A bridge is defined as a structure having an opening of more

span bridges depends

Presented in Table 2 are the numbers of

having a deck length of less

ry II includes bridges

friction test. The

of more than 150 feet. Apparently,

e bridges in category III, which depends on the traffic

defined solely for the

task. In reality, field friction testing may be conducted at variable speeds.

d network bridge deck inventory friction testing in

bridges were successfully tested, including 970 bridges on interstates, 125

count for approximately 20%

the bridges in categories II and III. During field testing, the typical test

speeds utilized by INDOT are 30 mph, 40 mph, and 50 mph. The target test speed is 40 mph to

avoid possible errors from data conversion. However, the test speed of 30 269

used on 2-lane roads, and 50 mph on interstates. A speed of higher than 50 mph may be used, but 270

is not recommended, particularly on bridge decks. 271

on interstates. The results demonstrated greater var272

It was notices that when applying brake at 60 mph, the test wheel experienced greater dynamic 273

contacts with the pavement surface. In addition, applying brake at 60 mph raised concerns over 274

operation safety and damage to tire. 275

Table 3 shows the summary of bridge deck friction performance by 276

network level. The bridges on interstates demonstrated the lowest average friction number and 277

the bridges on State routes demonstrated the 278

bridges on interstates and State routes experienced the same extent of variation (see coefficient 279

of variation in Table 3). To further examine the friction performance of bridge decks on different 280

highway systems, the bridge decks were divided into five groups such as Poor (FN<20), Fair 281

(FN=20 to 25), Good (FN=25-35), Very Good (FN=35282

Figure 3. It is shown that a large portion of bridge decks with p283

located on interstates. This indicates that the bridges on interstates tend to have more issues 284

associated with the deck surface friction than t285

a concrete bridge deck state. While transverse tines are commonly produced 286

the deck surface friction performance is very sensitive to the wearing action of vehicle tires.287

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TABLE 4 Statistics of Bridge Deck Friction 289

Highway System Average

Interstate 35.1

US Highway 41.4

State Route 47.2

290

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FIGURE 3 Distributions of 292

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avoid possible errors from data conversion. However, the test speed of 30 mph is commonly

lane roads, and 50 mph on interstates. A speed of higher than 50 mph may be used, but

is not recommended, particularly on bridge decks. INDOT R&D conducted trial tests at 60 mph

on interstates. The results demonstrated greater variations than those measured at lower speeds.

It was notices that when applying brake at 60 mph, the test wheel experienced greater dynamic

contacts with the pavement surface. In addition, applying brake at 60 mph raised concerns over

amage to tire.

Table 3 shows the summary of bridge deck friction performance by highway system

The bridges on interstates demonstrated the lowest average friction number and

the bridges on State routes demonstrated the highest average friction number. However, the

s on interstates and State routes experienced the same extent of variation (see coefficient

To further examine the friction performance of bridge decks on different

, the bridge decks were divided into five groups such as Poor (FN<20), Fair

35), Very Good (FN=35-45), and Excellent (FN≥

It is shown that a large portion of bridge decks with poor friction performance were

This indicates that the bridges on interstates tend to have more issues

associated with the deck surface friction than those on US highways and State routes.

While transverse tines are commonly produced on the deck surface

friction performance is very sensitive to the wearing action of vehicle tires.

of Bridge Deck Friction Numbers at Network Level

Average Standard Deviation Coefficient of Variation

35.1 10.3 29 %

41.4 9.0 22 %

47.2 13.8 29 %

Distributions of bridge decks with different friction performance

mph is commonly

lane roads, and 50 mph on interstates. A speed of higher than 50 mph may be used, but

INDOT R&D conducted trial tests at 60 mph

iations than those measured at lower speeds.

It was notices that when applying brake at 60 mph, the test wheel experienced greater dynamic

contacts with the pavement surface. In addition, applying brake at 60 mph raised concerns over

highway system at the

The bridges on interstates demonstrated the lowest average friction number and

highest average friction number. However, the

s on interstates and State routes experienced the same extent of variation (see coefficient

To further examine the friction performance of bridge decks on different

, the bridge decks were divided into five groups such as Poor (FN<20), Fair

≥45) as shown in

friction performance were

This indicates that the bridges on interstates tend to have more issues

hose on US highways and State routes. Indiana is

on the deck surface,

friction performance is very sensitive to the wearing action of vehicle tires.

at Network Level

oefficient of Variation

%

%

%

fferent friction performance

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CONCLUSIONS AND RECOMMENDATIONS 295

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Based on the results of the verification tests and network tests, several conclusions can be drawn 297

as follows: 298

One of the main concerns associated with friction testing on bridge decks is the length of 299

bridge (deck). If tested at the standard test speed of 40 mph, the bridge should be at least 88 feet 300

long. However, the minimum length varies with the test speed used in testing. Multiple test runs 301

were conducted to verify the reliability of bridge deck friction testing and evaluate the effect of 302

water. It can be concluded that a single test is capable of providing a friction number that is 303

reliable for inventory bridge deck friction test at the network level. 304

Surface texture was utilized to verify the accuracy of bridge deck friction testing. While 305

poor correlation between macro-texture and friction has been reported, a general rule of thumb is 306

that FN decreases as MPD decreases. In this paper, the average MPD of 0.172 is very small, 307

which agrees well with the low friction numbers. Based on the test results together with field 308

visual inspection, it can be concluded that a single test is capable of producing accurate test 309

result on the deck surface friction performance. 310

Based on the INDOT experience, network bridge deck testing may cover up to 30% of 311

bridges having a deck length of more than the minimum length. This provides very good 312

representation at the network level. In addition, it was indicated that the bridges on interstates 313

tend to have more deck surface friction issues than those on US highways and State routes. 314

It is recommended that network bridge deck friction testing should be conducted at 30 315

mph, 40 mph or 50 mph, depending on the highway speed and traffic condition. A higher speed 316

such as 60 mph is not recommended because of the potential errors, safety concerns and tire 317

damage. More effort should be made to investigate the nature and effect of micro-texture that 318

plays an important role in producing long-term friction performance with HFST overlays on 319

bridge decks. 320

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ACKNOWLEDGMENTS 322

323

The authors recognize the support from Barry Partridge, Tim Wells and Samy Noureldin of 324

INDOT to accomplish this task. The authors would also like to thank Karen Zhu, Patrick 325

Weaver, Victor Hong, and Jaffar Golkhajeh of INDOT and Rob Ladson of ITR Concession 326

Company LLC for their help in field testing and data processing. The contents of this paper 327

reflect the views of the authors, who are responsible for the facts and the accuracy of the data 328

presented herein, and do not necessarily reflect the official views or policies of the sponsoring 329

organizations. These contents do not constitute a standard, specification, or regulation. 330

331

REFERENCES 332

333

1. Shuo Li, Karen Zhu, Samy Noureldin, and Yi Jiang (2009). ”Evaluation of Pavement Friction 334

Performance on Interchange Ramps at Network Level.” Journal of Performance of 335

Constructed Facilities, 23(2), 109–114. 336

2. ASTM E274M, 2011, “Standard Test Method for Skid Resistance of Paved Surfaces Using a 337

Full-Scale Tire,” ASTM International, West Conshohocken, PA, 2011, 338

DOI:10.1520./E0274M-11, www.astm.org. 339

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3. ASTM E524-88, 2000, “Standard Specification for Standard Smooth Tire for Pavement Skid-340

Resistance Tests,” ASTM International, West Conshohocken, PA, 2000, DOI: 341

10.1520/E0524-88R00, www.astm.org. 342

4. Shuo Li, Samy Noureldin, and Karen Zhu (2007). “Realistic Approach for Enhancing 343

Reliability of Pavement Surface Friction Testing,” Journal of ASTM International, Vol. 3, 344

No. 9, 73-80. 345

5. ASTM E1845-09, 2009, “Standard Practice for Calculating Pavement Macrotexture Mean 346

Profile Depth,” ASTM International, West Conshohocken, PA, 2001, DOI: 1 DOI: 347

10.1520/E1845-09, www.astm.org. 348

6. Shuo Li, Samy Noureldin and Karen Zhu (2010). Safety Enhancement of the INDOT Network 349

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Indiana Department of Transportation and Purdue University, West Lafayette, Indiana. 352

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Pavement Surface Friction,” CD-ROM. TRB 91st Annual Meeting, Transportation Research 358

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Administration, U.S. Department of Transportation, 2004. 361