Evolution of Pavement Winter Roughness - Transportation Research ...

Evolution of Pavement Winter Roughness Nicolas Fradette, Guy Doré, Pascale Pierre, and Serge Hébert tributing factors of roughness are heavy traffic and freeze–thaw cycles. Driving conditions are directly influenced by this quality parameter obtained by a mathematical transformation of the longitudinal profile of the pavement surface. A high value for this parameter indicates that the road is in bad condition and in need of rehabilitation.

The functional service level of roads is quantified in terms of roughness. This parameter considers every road surface defect that causes passenger vehicle discomfort. Roughness is measured by a quality index, the international roughness index (IRI). Roughness gives an overall appreciation of road profile quality without, however, permitting a deeper analysis. The overall value of the IRI does not discriminate between the two main factors responsible for winter deterioration of roughness: the subgrade differential heave and crack heaving (winter tenting). Differential heave is the result of variability in frost susceptibility of subgrade. This phenomenon can be detected by isolating the long wavelengths produced at the road surface from the longitudinal profile. Crack heaving is a superficial phenomenon greatly influenced by the application of deicing salts. By isolating the short wavelengths from the profile, it is possible to highlight the influence of this phenomenon on deterioration. The goal of this research is to establish, with the use of a filtering technique of road profile, the contribution of these two main factors to winter deterioration of roughness on five road sections in the Quebec City, Canada, area. This study will then allow for the development of a tool to determine the dominant factor for longitudinal profile deterioration and therefore the use of the best technique to rehabilitate roads.

INTERNATIONAL ROUGHNESS INDEX CONCEPT Roughness is reported with the use of the international roughness index (IRI). This index is calculated from the longitudinal profile of a road. The longitudinal profile is obtained using a profilometer, which typically measures surface relative elevation every 150 mm. Typical profilometers allow simultaneous measure in the two wheel tracks and for speeds between 30 and 110 km/h. The calculations by which the IRI is determined are based on a mathematical model that represents the dynamic response of a vehicle to the road profile. This quarter car model simulates the vertical movement of the vehicle with respect to a sprung mass, which is a function of the suspension system, subject to variations in road profile. To summarize, this model enables us to simulate the movement felt by the passengers of a vehicle through a calculation of the vertical displacement of the vehicle frame induced by the road profile. The calculation is based on the following equation:

In the province of Quebec, Canada, flexible pavement deterioration caused by climatic variations (freeze–thaw) is an ever-present problem. To minimize the negative effects of climate, it is important to understand adequately the main factor that influences pavement deterioration. Road roughness is used to quantify the level of functional service. This indicator, measured in winter, quantifies frost action and helps choose the appropriate rehabilitation techniques. It is difficult to differentiate the relative importance of the two main factor’s contribution to the winter deterioration of pavement surface roughness. These two factors are the frost susceptibility of the subgrade and frost heaving of transverse cracks (often referred to as winter tenting). This research aims at establishing, on the basis of a more indepth study of winter deterioration on five road sections in the Quebec City area, the contribution of these two main factors. The study is based on two sections of Highway 369 in Sainte-Catherine, two sections of Highway 367, and one of Highway 40 in Saint-Augustin (Figure 1).

IRI =

1 L

n

∑

Zs − Zu

(1)

i =1

where Zs Zu L n

= = = =

position of the sprung mass, position of the vehicle frame axle, length of the profile, and number of points in the longitudinal profile.

The IRI is the summation of relative vertical displacements over a given distance covered, either in meters per kilometer or in millimeters per meter. The index varies from 0 to more than 10. Experience shows that a new road has an IRI between 0.8 and 1.2 and that 0 is a practically impossible value to obtain. An IRI of 10 stands for a hardly accessible road. The acceptable threshold for this parameter is a function of the speed allowed and of the road section traffic volume. Therefore, an IRI of approximately 3 is acceptable for a highway, whereas a secondary road can have an IRI of 4 or 5 before repairs are necessary. Surface distortions are characterized by amplitude and wavelength. Wavelengths typically vary from 0.1 to 50 m, although the amplitude can vary from a few millimeters to approximately 200 mm. The topography and surface layer macrotexture are not included in the IRI calculation. Only wavelengths between 0.7 and 45 m are considered. The Organisation for Economic Cooperation and Development (OECD) (1) specifies that the short and medium wavelengths are those

ROUGHNESS Roughness, because of its major effect on comfort and safety of road users as well as on the vehicle operation cost, is one of the main indicators of road condition or functional service level. The main conDepartment of Civil Engineering, Adrien-Pouliot Building, Laval University, Quebec City, Quebec G1K 7P4, Canada. Transportation Research Record: Journal of the Transportation Research Board, No. 1913, Transportation Research Board of the National Academies, Washington, D.C., 2005, pp. 137–147.

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FIGURE 1 Index map of five sites studied: #1 Highway 369, Section 1; #2 Highway 369, Section 2; #3 Highway 367, Section 1; #4 Highway 367, Section 2; and #5 Highway 40.

that are most likely to affect the safety of the road users. The distortions with short wavelengths can reduce the friction between the tire and the pavement and increase the risk of loss of control in the curves. The IRI gives an overall appreciation of the quality of the road profile without, however, allowing for a deeper analysis. The overall value does not differentiate between subgrade influence and superficial movements. To counter this shortcoming, it is necessary to proceed with a more detailed analysis of the longitudinal profile from the decomposition of the initial longitudinal profile according to the different wavelengths.

FILTERING OF INITIAL LONGITUDINAL PROFILE The visual analysis of the profile is important because it enables researchers to obtain an overall view of the section studied and to identify zones at risk. A more detailed analysis can be performed by filtering the profile as suggested by several authors (2–4). The road can be treated as a continuous random signal. To simplify analysis, the signal is considered to be the sum of many elementary

sinusoidal signals of different wavelength, amplitude, and phase. It is then possible to decompose the profile into different wavelengths. To accomplish this, many filtering techniques can be used (5). In this research, a simple filtering method based on a moving average technique was used. Data smoothing consists of taking away from the longitudinal profile database those values associated with short wavelengths by replacing each data point with the mean value of the adjacent points. The distance over which the elevation data are averaged is the filtering base and corresponds to the wavelength removed from the profile. For example, for elevations measured at each 150 mm, a moving average over 21 data points (10 on each side) would take away wavelengths shorter than 3 m. In addition, antismoothing filtering can be used to remove long wavelengths from the profile. The antismoothed profile can be obtained by subtracting the smoothed profile from the initial profile. Long wavelengths are generally associated with deformations occurring deep into the pavement system, whereas surface defects result in profile distortions over short wavelengths. Long wavelengths generate vehicle oscillations that make driving uncomfortable, whereas short wavelengths induce steering vibrations, which increase the risk of an

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accident. In this study, the data were smoothed and antismoothed for the 3 m wavelength to highlight short and long wavelengths that affect the longitudinal profile. IRI was then recalculated on smoothed and antismoothed profiles to facilitate quantification of the contribution on short wavelengths (3 m) on pavement roughness. After establishing the influence of the long and short wavelengths, it is then possible to recommend an applicable rehabilitation technique. Resurfacing might be an appropriate rehabilitation technique for pavements affected by short wavelengths. Long wave distortions suggest that differential frost heave might be the dominant cause of excessive roughness and might warrant partial or complete reconstruction of the pavement. FACTORS INFLUENCING IRI Many factors can cause premature degradation of road roughness. The most important are construction defects, heavy traffic, and freeze– thaw cycles. In this study, only frost action will be examined. The focus of the study will be to separate the effects of crack heaving caused by deicing salts (6, 7) and differential heave caused by the variability in frost susceptibility of the subgrade soils (3). METHOD By using a road profile analysis software developed in an earlier project (3, 4), different charts were produced during this study. First, charts illustrating the evolution of road profile as a function of distance for the two wheel tracks for each section provided a general analysis of the road surface. On these charts, the winter road profile evolution is not clear because the scale is usually greater than 1,000 m.

0

EB

GP

To highlight road profile deformations as frost progresses in the pavement structure, a few sections of 100 to 250 m were chosen. Next, to allow a more in-depth analysis, the profiles were filtered and charts illustrating the evolution of IRI over time for original, smoothed, and antismoothed profiles were produced (Figures 2 to 6). From these graphs, it is possible to observe the contributions of different wavelengths on road roughness degradation during winter. ANALYSIS FOR EACH SECTION STUDIED Highway 369, Section 1 Highway 369, section 1, which can be considered a local road, is an old section built on the alluvial terrace of the Jacques-Cartier River near Shannon. During a site visit, many longitudinal and transversal cracks, alligator cracks, and depressions were observed. In particular, at approximately 1 km from the beginning of the section, a significant profile disruption with large vertical distortions approximately 5 m long was noted. This particular event corresponds to the position of a culvert. Shallow ruts are an indication of the relatively small proportion of heavy trucks using this road. From Figure 2, it can be seen that the IRI is very high with values reaching 6.8 m / km at the end of winter. It appears that crack heaving and differential heaving in the underlying soil may contribute to IRI increase, which shows a significant increase when the frost depth reaches the silty sand on December 18 (Figure 2). An in-depth study of the section above the culvert (900 to 1050 m) shows that the condition of the road at this location experienced significant deterioration during winter (Figure 7). Long wavelength deformations appear to have the greatest influence on this road section. In fact, the short undulations of 5 to 15 m that appeared on the March 14 profile appear to be related to the variabil-

IRI non-filtered IRI smoothed, base length of 3 m IRI anti-smoothed, base length of 3 m Frost depth Thaw depth

8

40

80

IRI

SM (sat.)

Frost Depth (cm)

6

120

2

SP

160

200 10/21/02

0 12/10/02

1/29/03

3/20/03

5/9/03

6/28/03

Time FIGURE 2 IRI evolution and frost depth over time for Highway 369-1 [EB = bituminous concrete (asphalt pavement); GP = uniform gravels (mix of gravels and sand, very low content of fine particles); SM = silty sand (mix of sand and silt); SP = uniform sand (very low content of fine particles)].

140


2.8

0


EB

40

sat.

2.4

2

80

IRI

SP + GP

Frost Depth (cm)

GP

120

1.6

160

1.2

200

0.8

10/21/02

12/10/02

1/29/03

3/20/03

5/9/03

6/28/03

Time FIGURE 3

IRI evolution and frost depth over time for Highway 369-2.

0

5

40

4

80

3

120

2

SP + SM

Frost Depth (cm)

GP

IRI

EB

SM

160

SM (sat.)

1


200 10/21/02

0

12/10/02

1/29/03

3/20/03

Time FIGURE 4

IRI evolution and frost depth over time for Highway 367-1.

5/9/03

6/28/03


0

EB GP 50

141

3


SM

SP

100

IRI

Frost Depth (cm)

2

150

1

200

ML 250 10/21/02

0 12/10/02

1/29/03

3/20/03

5/9/03

6/28/03

Time FIGURE 5 IRI evolution and frost depth over time for Highway 367-2 [ML = inorganic silt and fine sand (rock dust, clayey or silty fine sand, low plastic clayey silt)].

0

GP

2

50

1.5

100

IRI

Frost Depth (cm)

SP

2.5 IRI non-filtered IRI smoothed, base length of 3 m IRI anti-smoothed, base length of 3 m Frost depth Thaw depth

EB

1

150

0.5

SP + SM + GP

200 0

10/21/02

12/10/02

1/29/03

3/20/03

Time FIGURE 6

IRI evolution and frost depth over time for Highway 40.

5/9/03

6/28/03


Elevation (mm)

142

Distance (m)

Elevation (mm)

(a)

Distance (m) (b) FIGURE 7 Profile comparison at beginning and end of winter for 900- to 1,050-m milepost, Section 369-1: (a) December 18 and (b) March 14.

ity of the soil probably caused by the alternating sequence of silty soils with granular river deposit (Figure 7). The poor transitions next to the culverts are probably the cause of a significant distortion just before the 1000-m mark. The deformations caused by frost heave in this area are as high as 90 mm.

Highway 369, Section 2 This road section, which was resurfaced approximately 1 year before the study, is located near Shannon and is underlain by river deposits that are sometimes in contact with marine deposits. Few cracks were observed on that section, but three significant bumps probably caused by geologic contacts were noted. The first two bumps, at 150 and 300 m, are located on each side of a small creek crossing the

road. A more silty section along this river could be the cause of these anomalies. The bump located 1,400 m from the beginning of that section appears to coincide with a contact between the alluvions and marine deposits. In an analysis of Figure 3, even if the IRI remains relatively low, it appears to be influenced by the differential heave of the underlying soil, whereas the IRI curve follows closely but slightly above the antismoothed curve. Figure 8 illustrates the geologic contacts situated on each side of the creek and shows the presence of significant distortions at these locations. The differential heave that appears to have occurred in the previous years continues to deteriorate as winter progresses. Another subsection where the last bump is located, at approximately 1.4 km from the beginning of the section, is illustrated in Figure 9. At this location, it is possible to observe new undulations that are from 5 to a bit more than 10 m long and from 10 to 60 mm high. Differential heaving occurring in the sub-

143

Elevation (mm)


Distance (m)

Elevation (mm)

(a)

Distance (m)

(b) FIGURE 8 Profile comparison at beginning and end of winter for 100- to 350-m milepost, Section 369-2: (a) December 18 and (b) March 14.

grade soil appears to be an important factor in IRI evolution for this road section.

Highway 367, Section 1 Section 1 of Highway 367 is built on a heterogeneous till deposit in the municipality of Sainte-Catherine. This road section, affected by a severe crack-heaving problem, was resurfaced 2 years before the study. During a site visit, many transverse cracks and ruts could be observed. This road section supports a large volume of heavy traffic. Furthermore, two significant deformations, probably caused by geologic contact, were observed in the section. The first occurs 300 m from the beginning of the section where a sandy river deposit is in contact with the glacial till deposit. Moreover, a bad transition appears to exist at approximately 550 m where the glacial till is in contact with bedrock. It is possible to observe in Figure 4 that the IRI reaches high values of approximately 4.6. This figure also highlights the effects of heaved cracks on IRI variations. It is interesting to see how well

the short wavelength variations follow the evolution of total IRI, which suggests that crack heaving is in good part responsible for deterioration of IRI. IRI drops rapidly from March 14 when cracks return to their original positions after a partial thaw of the top part of the pavement and way before subgrade thawing. The IRI caused by the long wavelengths that still show a small influence starts to diminish later at the end of winter. Two sections of this road were chosen to proceed with a more in-depth study. The first, at approximately 300 m, is located where there is geologic contact with the “Rivière aux pommes” deposits (Figure 10). For that section, it appears to be the short wavelength deformation that dominates the profile (presence of many little peaks on the March 14 profile). The other section studied is located at approximately 550 m, where there is contact with the bedrock (Figure 11). The profile at the end of the winter is strongly modified. It is possible from these two sections to observe that crack heaving has already started at the beginning of December and is greatly accentuated on the March 14 profile. For the long wavelength deformations close to the geologic contacts, distortions are already present at the beginning of winter but are amplified by frost action. In


Elevation (mm)

144

Distance (m)

Elevation (mm)

(a)

Distance (m) (b)

FIGURE 9 Profile comparison at beginning and end of winter for 1,310- to 1,440-m milepost, Section 369-2: (a) December 18 and (b) March 14.

fact, large deformations, which become more obvious with time, were noted near the contacts. These two phenomena appear to have played a role in the deformation of this part of the road even if crack heaving appears to be predominant.

Highway 367, Section 2 This section, located in the municipality of Saint-Augustin, was built at the limit between a very heterogeneous till deposit and shallow sea deposits of sand and gravel. The first 130 m of the section presents significant longitudinal and transversal cracks. This is mostly because of the old age of the pavement built approximately 20 years ago. The total IRI of this section of the road reached a critical value of 9 during the period of monitoring. The other part of the section, located between 130 and 1,200 m, was rebuilt recently. However, this part already

shows signs of deterioration. In fact, deformations are felt while driving over the section. The IRI increase is, however, relatively small and weak (0.8 m/km). By looking at the IRI evolution over time for section 2 of Highway 367 (Figure 5), the IRI appears to be influenced mainly by the subgrade soil. The antismoothed IRI remains relatively stable during winter, whereas the smoothed IRI increases until April 7, following closely the evolution of the nonfiltered IRI. This behavior clearly shows the contribution of the differential heaving in subgrade soil on winter roughness deterioration.

Highway 40 This section of Highway 40 is built in an area where glacial till and deep marine deposits coexist. The pavement is underlain by gravely sand. This section, located in the municipality of Saint-Augustin, is

145

Elevation (mm)


Elevation (mm)

Distance (m) (a)

Distance (m) (b) FIGURE 10 Profile comparison at beginning and end of winter for 200- to 400-m milepost, Section 367-1: (a) December 18 and (b) March 14.

in relatively good condition. The IRI evolution over time (Figure 6) shows that the IRI remains relatively stable as winter progresses. The maximum IRI reached is approximately 2 m/km, which shows the good condition of the road. This good performance is probably due in part to the thick 700-mm gravel base for this road (Figure 6). The same graph shows that differential heave in the subgrade soil appears to contribute to the increase in IRI. The increase is, however, better explained by the antismoothed profile, suggesting that surface phenomena have a dominant effect on the winter roughness evolution. A slower progression of the freezing front, probably caused by a momentary warming of the temperature, has an immediate effect on the IRI, which decreases for the same period from the beginning to the middle of January.

DISCUSSION OF RESULTS This study has shown that the development of winter roughness is greatly influenced by differential frost heaving in the subgrade soil and by frost heaving of transverse cracks.

Influence of Subgrade Soils Three conditions must coexist to have differential frost heaving: (a) the freezing front must reach the subgrade soil, (b) the subgrade soil must be frost susceptible, and (c) the subgrade soil must be heterogeneous so that there is a difference in heave at the surface of the road. The


Elevation (mm)

146

Elevation (mm)

Distance (m) (a)

Distance (m) (b) FIGURE 11 Profile comparison at beginning and end of winter for 440- to 600-m milepost, Section 367-1: (a) December 18 and (b) March 14.

first condition is largely met for all sections studied. Frost susceptibility and heterogeneity of the subgrade are also present, to various degrees, for all sections. River deposits of the Highway 369 section are sometimes in contact with silty soils or marine deposits. As for the sections of the Highway 367 and Highway 40, they were built on a heterogeneous till that is variable and frost susceptible. Moreover, marine deposits are present nearby. Sections 1 and 2 of Highway 369 were particularly affected by differential heave during this study. The deformations appearing during winter varied, for the most part, between 5 and 15 m in length. This suggests that differential heave was caused primarily by subgrade heterogeneity. Finally, there appears to be a direct influence between the development of differential frost heave and the moment when the freezing front reaches fine-grained subgrade soils.

Effect of Crack Heaving on Winter Roughness Development Crack heaving is a surface phenomenon that typically occurs at a shallow depth in the granular base. It has been associated with the infiltration of brine (from deicing activities) through pavement cracks (6). In the current study, Sections 369-1, 367-1, and the first 130 m of section 367-2 were the most affected by this phenomenon. Sections 369-1 and 367-2 (the first 130 m) are old sections with extensive cracking that are expected to show poor performance problems with respect to crack heaving. However, Section 367-1, which was repaved 2 years before the study already shows severe crack heaving problems. The volume of heavy traffic has probably contributed to rapid crack reflection through the new overlay. The granular base material


also probably is still contaminated by deicing salt maintaining heterogeneous frost action in the pavement structure. For some sections, a decrease in the progression of the freezing front can be observed, probably caused by a short period of milder temperatures. As a consequence, lower antismoothed IRI are observed for the same period. In summary, crack heaving is an important factor of pavement roughness deterioration during winter. The problem is characterized by short wavelength deformations. A roughness increase also occurs early in the winter, generally before the frost front reaches the subgrade soil, and it decreases rapidly during the first mild periods at the end of winter.

Limits of the Method A difficulty encountered in this study comes from the use of the profilometer to make roughness measurements. Because the transversal roughness of a road is quite variable, the overlapping of twodimensional profiles measured at different moments would require the vehicle to pass on the same wheel path or within a few millimeters. It is thus difficult to measure the real winter evolution of roughness. The use of the filter also can be a source of errors. Because no filter is perfect, some unwanted wavelengths are always present. Furthermore, parasitic effects are observed in the profile, creating a distortion of the remaining signal.

CONCLUSION AND RECOMMENDATIONS Even if the effect of freezing and thawing are relatively well understood and described in the literature, it is still difficult to predict pavement performance and more specifically roughness development during the winter. This difficulty is in part because of the poor understanding of differential frost heaving and the lack of reliable prediction tools. It is also caused by the difficulty in identifying the effects of the differential subgrade heave and of the crack heaving on winter deterioration of roughness. This study provides information that will contribute to an increase the level of understanding of the relative importance of these two factors for these five test sections in the Quebec City area. Analysis of the data collected during winter 2002–2003 shows that IRI increase during winter can be a severe problem. On the basis of observations made on other highways in the Province of Quebec, IRI increase can reach and even exceed 4.0 m/km. The IRI increase recorded during this study reached 2.5 m/km during the winter of 2003. The study made it possible to associate the deterioration of the road roughness to a main deterioration mechanism. The figures illustrating the longitudinal profiles plotted against distance during a complete winter season helped to obtain an overall view of road deterioration. From these graphs, it was possible to study the behavior of specific sections and to identify and characterize the distortions appearing during winter. In addition, from observations of the evolution of the smoothed and antismoothed IRI compared with that of the total IRI, it was then possible to estimate the relative importance of the contributing mechanism. These figures, which were associated with frost and thaw depth, also allow researchers to associate IRI fluctuations with the progression of the freezing front. It has been

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observed that antismoothed IRI increases rapidly as a front propagates through the pavement structure for pavements affected by the crack heaving process. In addition, when the freezing front reaches a high frost-susceptible soil, there is a clear increase of the smoothed IRI. During thawing, most of the antismoothed IRI reduction occurs before the thaw front reaches the subgrade soil, probably caused by the settlement of heaved cracks. The reduction of the smoothed IRI will in turn occur late in the thaw process when the thaw front has reached the subgrade soil. In summary, wavelength analysis of longitudinal profiles can help to identify pavement performance problems. In a frost heave context, a significant proportion of short wavelength deformations indicates that the pavement is affected by deterioration mechanisms occurring at shallow depth in the pavement. Moreover, a high proportion in long wavelengths indicates that distortions are occurring in the subgrade soil. On the basis of this analysis, it is possible to recommend a rehabilitation technique adapted to mechanisms responsible for winter roughness. In this study, long wavelength deformations were typically between 5 and 12 m for the few sections studied and are probably associated with intrinsic variability of the soil.

ACKNOWLEDGMENTS The authors acknowledge the participation of the Ministère des transports du Québec to this project. All the data used in this study were collected and made available to the researchers by the agency. The authors also thank the personnel of the Service des chaussées du MTQ and more specifically Yves Savard and Gaetan Caouette, for their excellent technical support during the entire project.

REFERENCES 1. Organization for Economic Cooperation and Development. Caractéristiques de Surface des Revêtements Routiers: Leur Interaction et Leur Optimisation, Recherche en Matière de Routes et de Transports Routiers. Paris, 1984. 2. Vaillancourt, M., P. Perraton, D. Dorchies, and G. Doré. Décomposition du Pseudo-Profil et Analyse de L’indice de Rugosité International (IRI), Canadian Journal of Civil Engineering, Vol. 30, 2003, pp. 923–933. 3. Doré, G., M. Flamand, and S. Tighe. Prediction of Winter Roughness Based on Analysis of Subgrade Soil Variability. In Transportation Research Record: Journal of the Transportation Research Board, No. 1755, TRB, National Research Council, Washington, D.C., 2001, pp. 90–96. 4. Doré G., M. Flamand, and P. Pierre. Analysis of Wavelength Content of the Longitudinal Profiles for C-LTPP Test Sections, Canadian Journal of Civil Engineering, Vol. 29, No. 1, 2001, pp. 50–57. 5. University of Michigan Transportation Research Institute. UMTRI Roughness Home Page. http://www.umtri.umich.edu/erd/roughness/index.html. Accessed May 9, 2005. 6. Doré, G., J.-M. Konrad, and M. Roy. Role of Deicing Salt in Pavement Deterioration by Frost Action. In Transportation Research Record 1596, TRB, National Research Council, Washington, D.C., 1997, pp. 70–75. 7. Kestler, M. A., A. S. Krat, and G. Roberts. Winter Tenting of Highway Pavements. Cold Regions Impacts on Civil Works: Proc., 9th International Conference on Cold Regions Engineering (D. E. Newcomb, ed.), ASCE, Reston, Va., 1998, pp. 501–512.

The Frost Action Committee sponsored publication of this paper.