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City of Saskatoon’s Pavement Management System: Network Level Structural Evaluation
Colin Prang, P.Eng.
City of Saskatoon
222 – 3rd Avenue North
Saskatoon, SK, Canada, S7K 0J5
Phone: (306) 975-2487
Email: colin.prang@city.saskatoon.sk.ca
Diana Podborochynski, E.I.T
PSI Technologies Inc.
221 Jessop Avenue
Saskatoon, SK, Canada, S7N 1Y3
Phone: (306) 477-4090
Email: dpodborochynski@pavesci.com
Roanne Kelln, E.I.T
PSI Technologies Inc.
221 Jessop Avenue
Saskatoon, SK, Canada, S7N 1Y3
Phone: (306) 477-4090
Email: rkelln@pavesci.com
Curtis Berthelot, Ph.D., P.Eng.
Professor, Department of Civil and Geological Engineering
University of Saskatchewan
57 Campus Drive, Saskatoon, Saskatchewan
Canada, S7N 5A9
(306) 966-7009
Email: Curtis.Berthelot@usask.ca
Word Count: 5330
Table and Figures: 8 x 250 = 2000 word equivalents
Total Words: 7330 words
Submitted To:
Transportation Research Board
Transportation Research Record
November 8, 2011
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 2
ABSTRACT: Pavement management systems (PMS) combine economics and engineering to derive cost-effective
solutions for road maintenance and reconstruction. Since 1993, the City of Saskatoon (COS) has
employed a PMS that focuses on pavement surface deterioration and ride quality to measure the
performance of the city‟s road network. However, reliably predicting the structural condition of roads
based on surface distress information can be very difficult; furthermore, structural road issues are the
most intensive and costly to rehabilitate. The COS started using heavy weight deflectometer (HWD)
measurements to assess the structural condition of the COS road network in 2006.
Since it is difficult to distinguish between certain surface distresses, like top down cracking, from
structural distresses, such as fatigue cracking, HWD structural information may be beneficial in assessing
the condition of the road structure and the corresponding treatment needed. Therefore, using COS
network level PMS surface distress data and condition ratings, the effect of using structural data as
measured by HWD is examined in this paper. Two neighborhoods in Saskatoon were analyzed using
typical COS PMS surface distresses and HWD deflection measurements.
The results of structural condition assessments complement and enhance the findings of surface
condition assessments. The risks posed by using surface condition assessments can be mitigated by using
structural condition assessments in addition to surface condition assessments. Ultimately, the use of
structural asset management will reduce the risk of a significant road failure and subsequent high
expenditures to fix such a failure.
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 3
INTRODUCTION
The American Association of State Highway and Transportation Officials (AASHTO) defines Pavement
Management Systems (PMS) as a “set of tools or methods that assist decision-makers in finding optimum
strategies for providing, evaluating, and maintaining pavements in a serviceable condition over a period
of time” (1). Generally, PMS have components of data collection and condition monitoring, data and
condition state analysis, treatment implementation, cost analysis, and feedback. PMS can improve the
efficiency of decisions and provide cost effective treatment strategies; this is turn improves the pavement
network and allows for funds to be properly allocated (1,2). PMS integrate economics with engineering
to optimize road decisions in a cost-efficient manner.
Since their development in the 1960‟s, PMS have used surface distresses to make decisions
regarding maintenance and rehabilitation treatment timing and scope (1,2). Agencies have come to
realize limitations of using surface distresses to quantify the structural capacity of pavements (3). Often,
by the time surface distress measures indicate that a road has structurally failed, the structural
deterioration has reached such a severe state that the road usually requires full rehabilitation or
reconstruction, preventing the optimization of maintenance and rehabilitation treatments. Structural
condition assessments based on surface condition often result in reactive as opposed to preventative
preservation treatments (3,4).
PMS are conducted at the network level or project level depending on the detail of information
required. Project level PMS are detailed and include information such as soil conditions and structural
capacity, in addition to surface distresses. Network level PMS are less detailed and are often limited to
surface distresses only. Network level PMS prioritize projects based on the needs, benefits, and costs of
the whole system (5).
Since PMS can have a great effect on agency budgets and fund allocations, PMS can be an
important component of an asset management system. Asset management systems value an agency‟s
infrastructure over its lifetime (6). For managing road infrastructure, estimates of the condition of the
road network are used to allocate limited funds for maintenance and rehabilitation treatments within the
network. An agency‟s PMS needs to adequately measure the structural integrity of its roads to achieve an
optimized road maintenance and rehabilitation strategy.
City of Saskatoon PMS Background
Prior to 1993, the City of Saskatoon (COS) did not employ a Pavement Management System (PMS).
Maintenance treatments were conducted on a reactive basis, often following a citizen‟s complaint (7).
Maintenance and rehabilitation treatments were not planned and were instead completed on roads with the
most severe surface distresses first (7). A “worst first” scenario was developed (3).
In 1993, the COS initiated a PMS that focused on pavement surface deterioration and ride quality
to allocate intermediate treatments and to measure the performance of the city‟s road network. Since
1993, the COS-employed PMS has evolved in terms of distresses and condition rating system. COS PMS
relies on surface deterioration and ride quality to measure road network performance (4). The COS road
network is divided into four road classifications: local, collector, arterial, and expressway. Road
classifications are determined based on estimates made at the time of construction of the road‟s future
traffic volumes and function. Budget funding is allocated amongst these classes.
Local roads are low volume roads with less than 1,500 vehicles per day and very few large trucks.
Local roads are used for accessibility and are constructed with thinner pavement structures typically
consisting of 50 mm hot mix asphalt concrete (HMAC), 125 mm granular base, 150 mm subbase, and 150
mm subgrade compaction. The local road class also includes industrial local roads that carry over 10
percent truck traffic in industrial areas of Saskatoon. Industrial local roads are subject to heavy, slow
truck traffic and are typically construction with 80 mm of HMAC, 150 granular base, 350 subbase, and
300 mm of prepared subgrade.
Collector roads move traffic from local roads to arterial roads and carry up to 12,000 vehicles per
day. Collector roads have less than two percent truck traffic but carry the majority of COS transit routes.
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 4
Collector roads are typically built with 80 mm of HMAC with 150 mm granular base, 225 mm subbase,
and 300 mm of prepared subgrade.
Arterial roads carry up to 30,000 vehicles per day and move traffic from housing subdivisions to
their day-time destinations. Arterial roads carry less than five percent truck traffic. Arterial roads are
typically constructed with 100 mm HMAC, 150 mm granular base, 300 mm subbase, and 300 mm of
prepared subgrade.
Expressway roads are high volume, high speed, and provide limited access. These roadways
carry traffic within the city and through the city. Traffic volumes on expressways typically exceed 30,000
vehicles per day and truck traffic can exceed ten percent. There are no standard pavement structures for
expressways. Expressways are designed specifically based on soil investigation data.
Presently, the COS PMS uses three visual surface distresses to determine the pavement condition
of the road network: International Roughness Index (IRI), rutting, and cracking (4). At the network level,
COS collects surface distress data every three years on its entire roadway network. Local and collector
roads surface distress data is collected on a third of the network annually. Arterial roads and expressways
surface distress data is collected every three years. Surface distress data is used to rate the condition of
each road to select maintenance and rehabilitation treatments across the network. If additional
information is required, project level data is collected for verification and structural design.
Table 1 describes the COS PMS condition states for minor and major roads. Condition state 1
represents a good condition state; condition state 8 represents a poor condition state. Raveling,
depression area, and cracking distress data is collected for local and collector roads; eight condition states
result based on the combinations and severity of these distresses. IRI and rutting distress data is collected
for arterial roads; four condition states result based on the combinations and severity of these distresses,
with IRI being the primary treatment indicator.
TABLE 1 City of Saskatoon PMS condition states.
Condition State Local and Collector Roads Arterial Roads
1 No defects meeting thresholds No defects meeting thresholds
2 Ravel threshold exceeded IRI threshold exceeded
3 Depression threshold exceeded Rutting threshold exceeded
4 Poor raveling and depression Poor IRI and rutting
5 Cracking threshold exceeded -
6 Poor cracking and raveling -
7 Poor cracking and depression -
8 Poor cracking, depression, and raveling -
Maintenance and Rehabilitation Treatments
The COS recently developed four treatment categories for the city‟s roads, based on their condition and
the effort required to improve their condition. The four conditions are:
1. Maintenance – roads that do not require any planned treatment, other than pothole patching, spray
patching, or sand crack sealing if necessary,
2. Preservation – roads starting to exhibit degradation (although not necessarily visible to the public),
where treatment will extend the time until a more extensive treatment is needed,
3. Restoration – roads with profile problems and rough sections, where treatments will improve
drainage and ride without enhancing the road‟s structural capacity, and
4. Rehabilitation – roads with structural failures as evidenced by shear failures, potholes, and
significant cracking, where treatments improve the structural capacity of the road.
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 5
While the costs of preservation treatments range from $1 to $10 per m2 in the COS and the costs of
restoration treatments range from $12 to $35 per m2, the costs of rehabilitation treatments is far more
expensive, ranging from $50 to $130 per m2.
Limitations of Current PMS
The American Association of State Highways Officials (AASHO) performance prediction model
developed during the AASHO Road Test in the 1960‟s illustrates how public opinion determines the way
agencies manage pavement. Although public opinion is of great importance for COS, it should not be the
primary deciding factor for when a treatment is applied to a pavement. While surface deterioration and
ride quality are the road characteristics most recognized by the public, these characteristics do not
accurately assess the causes of pavement distress or the resulting structural condition of the road. Using
historical performance models based on public opinion to derive long term pavement preservation
allocations does not address the physical performance of the road structure itself in real time.
The current visual surface distresses measured in COS PMS are limiting. Using roughness
ratings to measure road network performance stems from the AASHO Road Test conducted in the 1960s
and does not reflect the structural capacity of the pavement structure (1). Although cracking is estimated
during surface distress data collection, information on the cause of cracking is not collected. For example,
on arterial roads, IRI and rutting are the primary indicators of condition state; cracking is only detected by
IRI measures when the road‟s lateral and transverse variations become too high and the ride
correspondingly becomes too rough. Therefore, moderate cracking often goes unnoticed and structural
damage, moisture infiltration, and permanent deformation can occur. Fatigue cracking can increase
rapidly once it develops and it has been found that a road structure can fail without exceeding the
treatment thresholds for IRI and rutting measurements. Even low severity fatigue cracking is an indicator
of structural deterioration.
While recommended treatments vary depending on surface distress condition threshold
differences, the actual condition state of a road can be overlooked, either rated to be in a good condition
state when it is performing poorly or vice versa. However, lowering the thresholds would result in
treatments that are untimely and not cost effective. Figure 1 illustrates a COS road that was rated as good
by the PMS; further inspection shows significant fatigue cracking and structural failure.
FIGURE 1 City of Saskatoon PMS rated road in good condition state.
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 6
With regards to road classification, there is currently no separate analysis for industrial local
roads. Industrial local roads are lumped in with local roads, despite the significant difference in load
spectra. While local roads carry little more than personal vehicles, industrial local roads carry slow
moving, heavy truck traffic. As such, the loading on Industrial local roads are substantially more than the
loading on residential local roads.
Furthermore, current PMS do not accurately reflect the structural performance of a pavement with
respect to applied load spectra. For example, the current PMS condition state of a road does not reflect
whether a road has adequate structural capacity to accommodate a bus route, detour, or additional heavy
truck traffic (8). In Saskatoon, unscheduled detours have resulted in the structural failure of local and
collector roads. Figure 2 illustrates the pavement surface of a COS road that was subjected to a detoured
bus route. Substantial surface distresses resulted and the road structure had to be reconstructed.
FIGURE 2 City of Saskatoon road after application of a bus route detour.
Several neighborhoods in the COS are subject to subsurface moisture problems that are not
quantified in surface distress surveys. In addition to poor draining and moisture susceptible subgrades,
some areas of Saskatoon are subject to high water tables. Subsurface moisture can weaken pavement
structural layers and cause structural failures (9).
COS PMS identifies preservation treatments well, but is limited in the ability to correctly identify
locations requiring rehabilitation treatments.
Determining the Structural Capacity of a Road
Reliably predicting structural condition based on surface distress information can be very difficult. There
are testing methods available to quantitatively characterize a pavement structure and determine structural
capacity of the road (10,11). The structural capacity of a road can be determined using both destructive
and non-destructive methods.
The most commonly used destructive test method is coring the pavement structure. Coring
determines the layer thicknesses of the road structure and the physical properties of the road materials.
Cores can be tested in the laboratory to determine stiffness and strength. Coring is expensive and time
consuming. Due to its destructive nature, coring is not applicable at the network level for PMS.
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 7
Two common non-destructive methods are the Benkleman beam test and the heavy weight
deflectometer (HWD) test. The Benkleman beam test is conducted on a pavement surface and measures
the deflection of the pavement structure under one fixed load (11). The Benkleman beam test is common
for highways and urban road tests. One of its drawbacks is that only one load can be applied at a fixed
load rate; varying loads and load rates cannot be applied.
Like the Benkleman beam, the HWD measures the deflection of a pavement structure when a
load is applied. However, the HWD is capable of testing the deflection of a pavement under varying load
spectra, thus better representing field state conditions and realistic truck traffic loads. HWD measurement
have been used in road engineering applications to assess the structural integrity of pavement structures
across typical commercial truck loads (3,4,9,11,12,13). Resultant pavement deflection profiles are used
to determine the structural condition of the road beyond the surface of the road. Using deflections to
characterize pavement structure responses, as measured by HWD, have been shown to be a good indicator
of structural performance (14,15,16). Aggregate course deterioration and the resulting potential damage
can be identified by HWD measurements (16). The deflection profiles can also be used to calculate
pavement structure layer stiffness and to determine the deflection sensitivity across load spectra (13).
The COS has collected network level HWD data since 2006 and has built a database of over
4,000 individual drop locations with information under load spectra of typical commercial truck loadings
experienced in Saskatoon from secondary legal load limits to primary legal load limits. Figure 3
illustrates the drop locations in Saskatoon.
FIGURE 3 City of Saskatoon HWD drop locations.
Since it is difficult to distinguish between surface distresses and structural distresses, HWD
structural information may be beneficial in assessing the condition state of the road structure and the
corresponding treatment. Therefore, using COS network level PMS surface distress data and condition
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 8
ratings, the effect of using structural data as measured by HWD is examined in this paper. Two
neighborhoods in Saskatoon were analyzed using typical COS PMS surface distresses and HWD
deflection measurements.
OBJECTIVE & SCOPE
The objective of this study was to compare surface and structural distress measurements for two
Saskatoon neighborhoods. The end goal was to determine if pavement structure performance data
contributed to the PMS; it is hypothesized that structural information would be beneficial in COS PMS.
The two neighborhoods examined in this study are Briarwood and Parkridge. Roads measured in
these neighborhoods include local and collector roads. HWD and surface distress data was collected in
the same year, for each neighborhood, at the network level. The individual deflection drop values for
primary highway weights were averaged over roadway segments. The segments were assigned good, fair,
and poor structural values.
Local roads were considered in a poor structural condition state if the average HWD segment
deflections exceeded 1.75 mm. The segment was considered fair if the average HWD deflection was
between 0.95 mm and 1.75 mm. If the HWD deflections averaged less than 0.95 mm, the segment was
rated good. Collector roads were considered in poor structural condition state if the average HWD
segment deflections exceeded 0.95 mm. The segment was considered fair if the average HWD deflection
was between 0.65 mm and 0.95 mm. If the HWD deflections averaged less than 0.65 mm, the segment
was rated good.
For surface distress assessments, streets that did not meet any treatment threshold were
considered good. Streets that met the thresholds for preservation or rehabilitation treatments were
considered fair. Streets that met the threshold for rehabilitation were considered poor.
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 9
NETWORK LEVEL SURFACE AND STRUCTURAL ASSESSMENT
Parkridge Neighborhood
Located on the south west side of Saskatoon, the Parkridge neighborhood was constructed mainly from
1979 to 1983, with some additional construction in the late 1990s and early 2000s. The Parkridge area
has a till subgrade and a low water table, although the neighborhood directly north of Parkridge has
certain areas with high water table issues. No roads in the Parkridge area have been reconstructed since
their initial construction, and the expected service life of Parkridge roads is in excess of 70 years.
Figure 4 presents the surface and structural ratings of local (Figure 4a) and collector (Figure 4b)
roads in Parkridge. As shown in Figure 4, the surface condition rating of Parkridge‟s local roads was
overall good, with 95.6 percent of local roads rated good and only 3.7 percent rated poor. The surface
condition ratings of Parkridge‟s collector streets was also good, with 85.1 percent rated good, 14.9
percent rated fair, and no roads rated poor. As seen in Figure 4, the structural ratings for Parkridge
coincided relatively well with the surface ratings. The majority of local and collector roads rated good
structurally, and no roads of either category were considered structurally poor. In Parkridge, 68.4 percent
of local roads and 88.3 percent of collector roads rated good structurally.
Figure 5 presents geographic maps of Parkridge, showing the surface condition and structural
condition ratings. Roads in good, fair, and poor conditions are shown in green, yellow, and red
respectively. For various road segments in Parkridge, the surface rating condition coincides relatively
closely with the structural rating condition. For roads where there was a difference between surface and
structural ratings, the difference was from good to fair.
Based on the surface and structural ratings, there are some local and collector roads in need of
surface treatments, as shown by the surface ratings, but structural issues are not the foremost concern for
the roads in Parkridge.
a) Local roads
b) Collector roads
FIGURE 4 Parkridge surface and structural condition class.
95.6%
0.7% 3.7%
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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e of
Road
s of
Giv
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urf
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Rati
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Surface Rating
68.4%
31.6%
0.0% 0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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e of
Road
s of
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tru
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Structural Rating
85.1%
14.9%
0.0% 0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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Road
s of
Giv
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urf
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Rati
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Surface Rating
88.3%
11.7% 0.0%
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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e of
Road
s of
Giv
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tru
ctu
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Rati
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Structural Rating
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 10
a) Surface condition rating
b) Structural condition rating
FIGURE 5 Parkridge condition rating maps.
Hart Rd
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tby C
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Highway 7
11th
St W
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 11
Briarwood Neighborhood
The Briarwood neighborhood is located in the south-east section of the COS. The local and collector
roads in Briarwood were constructed over an 11 year span from 1989 to 2010. The Briarwood area has a
clay subgrade and a high water table. In total, Briarwood has 139,239 m2 and 31,901 m
2 of local and
collector streets respectively.
Figure 6 presents the surface and structural ratings of local (Figure 6a) and collector (Figure 6b)
roads in Briarwood. As shown in Figure 6, the surface condition rating of Briarwood‟s local roads was
overall good, with 94.3 percent of the local roads rating good and 0.0 percent rating poor. The surface
condition rating of Briarwood‟s collector roads indicate that treatments are needed for some roads, since
33.8 percent of roads rated fair and 7.8 percent of roads rated poor. However, the surface ratings for
Briarwood are not indicative of the overall structural condition of the local and collector roads in
Briarwood. With regards to structural condition, Briarwood was the most poorly rated subdivision of
eleven surveyed in the COS. As shown in Figure 6, 82.7 percent of all local roads are in poor condition
structurally, even though 0 percent were classified as „poor‟ under the surface distress assessment.
Similarly, 72.7 percent of Briarwood‟s collector streets were classified as structurally fair and 27.3
percent were classified as structurally poor, despite the results of the surface distress survey indicating the
majority of Briarwood collectors are rated good.
Figure 7 presents geographic maps of Briarwood, showing the surface condition and structural
condition ratings. Roads in good, fair, and poor conditions are shown in green, yellow, and red
respectively. Notably, only three road segments in Briarwood had surface ratings that coincided with
structural ratings. For many road segments, the difference between surface and structural ratings was not
a difference between good and fair, but between good and poor.
While the surface network level survey may suggest that a series of maintenance treatments will
be needed in Briarwood, the structural network level survey shows that significant work and funding will
be required in the near future to maintain a reasonable level of service for these roads.
a) Local roads
b) Collector roads
FIGURE 6 Briarwood surface and structural condition class.
94.3%
5.7% 0.0%
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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e of
Road
s of
Giv
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urf
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Rati
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Surface Rating
0.0%
17.3%
82.7%
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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e of
Road
s of
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Structural Rating
58.4%
33.8%
7.8%
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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Road
s of
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Surface Rating
0.0%
72.7%
27.3%
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
Good Fair Poor
Per
cen
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Road
s of
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tru
ctu
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Rati
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Structural Rating
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 12
a) Surface condition rating
b) Structural condition rating
FIGURE 7 Briarwood condition rating maps.
8th St E
<Incorrect>
Taylor St E
Boych
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3
13
3
4
12
1
4
8
7
3
5
6
10
21
28
7
4322
5
45
21
14
29
4
19
62
17
55
13
60
65
42
39
16
4652
15
68
53
49
67
32
63
8
44
58
24
2
23
51
38
59
27
11
10
56
12
52
8th St E
<Incorrect>
Boych
uk D
r
Taylor St E
Bria
rga
te R
d
Braeside View
Brookhurst Cres
Banyan C
res
Blackburn Cres
Briarwood R
d
Brookmore Cres
Beechdale
Cre
s
Beech
mont L
ane
Beechm
ont Cres
Bayfield C
res
Bla
ckth
orn
Cre
s
Brookh
urst L
ane
Bro
oksh
ire C
res
Bellmont Cres
Bla
cksh
ire
Cre
s <unamed>
Briarvale Rd
Brookdale C
res
Braeburn C
res
Bayview Cres
Braeshire Lane
Brookmore Lane
Heritage Cres
Beechdale
Way
Heritage G
reen
Bayvie
w T
errBayview Close
Beechw
ood Cres
Bellmont Crt
Bro
okm
ore
Vie
w
Bee
ch
da
le C
rt
Beechm
ont Terr
Herold Rd
Bayfield Pl
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 13
DISCUSSION
As the goal of PMS is to optimize the maintenance and rehabilitation treatments applied across a road
network with regard to budgetary constraints, performance and life cycle predictions of road
infrastructure are necessary for network-level decision-making, both to determine expected treatments
and expected timelines for the treatments of all roads in the network. The findings of this study clearly
show that surface condition assessments do not provide information adequate for assessing the life cycle
and performance of road structures.
Although the surface condition assessments of Briarwood and Parkridge indicate relatively
similar conditions for both subdivisions, the structural condition assessments show drastic differences
between the conditions of the two subdivisions. While the structural condition ratings of the majority of
roads in Briarwood indicate that significant rehabilitation and reconstruction are needed in the near future,
the surface condition ratings only indicate that surface treatments will likely be needed for a number of
Briarwood‟s collector roads. In contrast, for the Parkridge local and collector roads, both the surfacing
and structural condition ratings show that Parkridge roads are generally in good condition, and will not
require major structural treatments in the near future. Also, while Parkridge is performing structurally
good after as much as 30 years of service, Briarwood is performing structurally fair or poor after 5 to 20
years of service. The ability of the HWD to assess structural performance of Briarwood roads provides
insight into upcoming maintenance and rehabilitation requirements. By evaluating structural conditions
of roads, the cost liabilities for the COS can be identified.
Flexible pavements in Saskatoon are highly dependent on subgrade type for their life cycle
performance. Due to the relatively thin layers of asphalt concrete and granular base used for typical COS
pavement designs, the material properties of the subgrade largely dictate the performance of roads. The
importance of subgrade type is evident in the comparison between Briarwood and Parkridge. While the
traffic loading and climatic conditions are similar for both subdivisions, Briarwood has a clay subgrade
prone to moisture problems while Parkridge has a till subgrade not subject to high moisture conditions.
The effect of subgrade type is clearly reflected in the structural assessment results found, as the local and
collector roads in the „high-and-dry‟ Parkridge area are predominantly classified as good structurally
while the roads in the low lying and wet Briarwood area are predominantly classified as poor or fair
structurally. The surface condition assessment was not sensitive to the subgrade of the road structure.
Even though Parkridge‟s local and collector roads exhibited less discrepancies between the surface and
structural condition ratings, structural condition assessments are still important for optimizing
maintenance treatments within the subdivision and within the city as a whole.
Although surface assessments provide valuable information about what maintenance or
preservation treatments are needed for each road, surface assessments are limited because they do not
address the mechanisms of road distresses or failures. While symptomatic treatment is effective for
maintenance and preservation issues with roads, further assessment is needed to diagnose structural issues
and to arrive at a timely and cost-effective rehabilitation strategy. Using only surface assessments poses
the risk to road agencies that structural issues may go undetected until the condition of the road reaches a
point where complete removal and replacement is the only treatment option, an intensive and costly
endeavor. For Saskatoon in particular, the greatest concern in road infrastructure is structural failure,
given the thin local and collector structures, the high moisture conditions becoming increasingly prevalent,
and the subgrade dependence of road designs.
CONCLUSIONS The results of structural condition assessments complement and enhance the findings of surface
condition assessments. The risks posed by using surface condition assessments can be mitigated by using
structural condition assessments in addition to surface condition assessments. Ultimately, the use of
structural asset management will reduce the risk of a significant road failure and subsequent high
expenditures to fix such a failure.
In looking at the surface and structural condition assessment for both Briarwood and Parkridge, a
greater disparity can be seen between the surface and structural condition assessments for the local roads
TRB 2012 Annual Meeting Paper revised from original submittal.
Prang, Podborochynski, Kelln, Berthelot 14
than for the collector roads. The thicker collector structures tend to „bridge‟ the poor subgrades more than
the local structures. Due to heavy traffic, structurally poor collectors are discovered sooner by surface
ratings as severe fatigue cracking becomes quite noticeable.
As the city continues to expand, structural condition assessments will become increasingly more
important, as limited budgets for road maintenance and rehabilitation must be stretched across an
expanding network. Urban expansion in Saskatoon is predominantly into low-lying areas with potentially
high water tables, similar to Briarwood.
The applicability of structural assessment extends beyond predicting performance to optimize
road treatments to being a valuable source of feedback for the structural design of roads in these areas.
Structural assessments can also be used at the project level to evaluate alternative road structural designs.
For instance, the use of recycled aggregates like reclaimed asphalt pavement (RAP) or crushed Portland
cement concrete (PCC) as base materials can be evaluated, even though these materials are not used in
conventional road structures. Also, the structural performance of roads with a drainage system, including
PCC or virgin crushed rock, weeping tiles, wick drains, geotextiles, or other materials or designs, can be
assessed. Over time, structural assessment can validate the long-term performance of these alternative
road structures, providing field-validation for future work.
ACKNOWLEDGMENTS
The authors would like to thank the City of Saskatoon and the University of Saskatchewan Centre in
Excellence for Transportation and Infrastructure for funding this project as well as for their assistance in
this research.
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TRB 2012 Annual Meeting Paper revised from original submittal.
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