Title

Determination of the intervention point for rehabilitation of dense graded asphalt wearing courses – the Western Australian Experience.

Author

Martyn Glover BSc MBA FIPWEA MIEAust

Abstract

The key to effective asset management of a road pavement, is the determination of an appropriate intervention point when replacing the asphalt wear course. An important tool in this exercise is the deterioration curve or prediction model for the pavement’s point of rapid decline in condition.

The sand sub‐grades of the metropolitan area in provide some of the best road pavement foundations in the world. When combined with Perth’s Mediterranean climate without any freeze/thaw it is considered that these road pavements have much longer life spans than roads elsewhere in Australia and the world.

The published deterioration models for road pavements and the wear courses from around the world have been traditionally used in pavement management systems that are available in Western Australia but in most cases they do not reflect the actual deterioration of the pavement.

This paper presents the final findings of a significant study in the Perth Western Australia which develops the deterioration curve based on nearly 10,000 kilometres of pavement monitored in some cases for in excess of 100 years and reconciled against recent ARRB pavement testing.

Introduction

In Western Australia there has been minimal research on the optimum intervention point for replacing dense graded asphalt wear courses. This has been in part due to our isolation but mainly due to Perth’s meteorology and geology which is very conducive to long lasting and very economic road pavements.

Although minimal research has been done, the road data available in Perth and all of Western Australia is exceptional as records have been kept originally by the Local Roads Boards and in the past 50 years by the State road authority, Main Roads Western Australia in a central repository which in the case of this research provides accurate data as far back as 1914. This data includes accurate visual assessments and both construction and resurfacing history of all roads in Western Australia in a consistent format. The initial purpose of this paper is to analyse the available data and develop an appropriate intervention point.

All Western Australian Local Governments are represented by the Western Australian Local Government Association. This organisation provides a report to Local Government each year on the level of expenditure on the road network each year and the resultant condition of the network as a result of the expenditure. The secondary purpose of this paper is to use this information to demonstrate the effectiveness of the current intervention strategies on the overall condition of the road network. Study Area

The use of asphalt surfacing in Western Australia is predominantly in the metropolitan area of Perth and the larger regional towns and cities. Consequently the study area has been limited to metropolitan Perth extended to include the City of . Most of this area is within a geological formation known as the Swan Coastal Plain. However it also includes area on the to the east of the metropolitan area.

Participating Local Governments

To provide an appropriate data set all thirty metropolitan Local Governments within the study area were contacted seeking permission to access their data and the following fourteen Local Governments agreed to be part of the project:

• , • , • , • , • City of , • Shire of Kalamunda, • , • , • , • , • , • , • and • .

There is variability in the subgrade soils across the Swan Coastal Plain consequently it was decided to split the participating Councils into three distinct groups as follows:

• The Perth Coastal Group including Belmont, Cottesloe, Joondalup, Melville, Nedlands, South Perth and Wanneroo collectively provide 3,657Km of asphalted roads. The subgrades in these areas are almost exclusively sand. • The Darling Range Group including Armadale, Gosnells, Kalamunda, Mundaring and Swan collectively provide 4,093Km of asphalted roads. The subgrades in these areas are either sand or lateritic soils of the scarp. • The Murray Coastal Group which marks the very southern area of the study area, comprises Mandurah and Rockingham and these provide 1,628Km of asphalted roads. The subgrades are predominantly sand however groundwater in these areas tends to be very shallow.

The Swan Coastal Plain

The Swan Coastal Plain is a 30 kilometre wide strip on the coast directly west of the Darling Scarp uplands running from Cape Naturaliste in the south to above the . This study will look specifically at the northern section of the Swan Coastal Plain, geologically referred to as the Perth Basin and aligned with most of the Perth metropolitan area.

In the area of the Perth basin, the Swan Coastal Plain is about 34 kilometres wide in the north, 23 kilometres in the south, and is bounded to the east by the Gingin and Darling Fault Scarps, which rise to over 200 metres above sea level. Geologically, the scarps represent the eastern boundary of Tertiary and Quaternary marine erosion.

The Swan Coastal Plain consists of a series of distinct landforms, roughly parallel to the coast. The most easterly landform comprises the colluvial slopes which form the foothills of the Darling and Dandaragan Plateaus and which represent dissected remnants of a sand covered, wave‐cut platform known as the Ridge Hill Shelf. To the west of the colluvial slopes lies the Pinjarra Plain, a piedmont and valley‐flat alluvial plain consisting predominantly of clayey alluvium that has been transported by rivers and streams from the Darling and Dandaragan Plateaus.

To the west of the Pinjarra Plain, the Bassendean Dune System forms a gently undulating aeolian sand plain about 20 kilometres wide with the dunes to the north of Perth generally having greater topographic relief than those to the south. The dunes probably accumulated as shoreline deposits and coastal dunes during interglacial periods of high sea level and originally consisted of mostly lime (calcareous) sand with quartz sand and minor fine‐grained, black, heavy‐mineral concentrations. Apart from a small local area to the south of Perth, the carbonate material has been completely leached leaving dunes consisting entirely of quartz sand.

West of the Bassendean Dune System are two systems of dunes which fringe the coastline. The most easterly of these is the Spearwood Dune System, which consists of slightly calcareous aeolian sand remnant from leaching of the underlying Pleistocene Tamala limestone. The most westerly dune system, which flanks the ocean, is the Quindalup Dune System (Safety Bay Sand), consisting of wind‐ blown lime and quartz beach sand forming dunes or ridges that are generally oriented parallel to the present coast, but which may also occupy blowouts within the Spearwood Dune System.

These sandy soils have particularly good road sub‐grade qualities which along with the Mediterranean climate contribute significantly to the longevity of road pavements constructed upon the soils.

Study Data Sets

There are three key data sets that will be utilised for the research. The first is the Roman II dataset which is the Road Management System utilised by 134 of the 140 Western Australian Local Governments. The basic road data recorded in this dataset includes road lengths, widths, construction date and resurfacing dates. . All of the participating Local Governments use Roman II. This system and its predecessors have provided asset management tools for Local Government since the 1970’s and the oldest data on asphalt was recorded in 1914 from the Town of Cottesloe.

The second dataset is the financial information contained in the annual Report on Local Government Road Assets and Expenditure published by the Western Australian Local Government Association (WALGA). This publication provides information on annual Local Government road rehabilitation expenditure which has been consistently reported in the same format for the past 15 years.

The final dataset is a series of field studies conducted by ARRB between 2003 and 2007 around Australia and including sites within the Perth metropolitan area. The study collected all recorded data on the road sections as well as current physical conditions including roughness, rutting, cracking and deflection.

Road Pavements

The sands of the study area of the Perth including the Safety Bay sand, Tamala Limestone and Bassendean Sand formations have California Bearing Ratios or CBRs in excess of 10.0, consequently the designed pavements are thin. Normally they consist of a relatively thin unbound sub‐base and base course overlaid with an extremely thin asphalt wear course.

In consideration of the minimal margin for error due to the ultrathin pavements the Department of Planning in WA decided to adopt a minimal standard for development. The Institution of Public Works Engineering Australia (WA Division Inc) Subdivision Guidelines Edition No 2.2, 2012 (the Guidelines) was the resultant adopted document and it prescribes the design standards for pavement thickness. The Guidelines establish that all pavements are designed in accordance with nationally recognised design documents and they also prescribe the anticipated design life of pavements as follows:

Unless specified otherwise by the Local Government, the permanent deformation of the granular pavement must have a minimum design life of 40 years. Unless specified otherwise by the local government asphalt must have the following minimum design life:

• open graded asphalt – 10 years; • dense graded asphalt 50 millimetres total thickness or less – 20 years fatigue life; and • dense graded asphalt greater than 50 millimetres total thickness – 40 years fatigue life.

The Guidelines provide three typical pavements ranging from 250mm to 280mm thick including an asphalt layer between 25mm and 65mm thick overlaying an unbound base of crushed rock and/or crushed limestone between 200mm and 250mm thick. Pavements constructed before the 1970’s have used limestone spalls and/or lateritic gravels as an alternative unbound portion overlaid by bituminous Macadam of varying thickness. These pavements tend to be even thinner than the more modern pavements with total pavement thicknesses recorded at less than 200mm however they still perform well today as both residential and distributor pavements.

Asphalts

In the recent past almost all metropolitan roads were paved with dense grade asphalt. The design for these asphalts was generally a maximum stone size of 10mm, predominantly granite, with a class 170 bitumen binder and at 50 blow marshal. The thickness was generally a minimum of 25mm. Resurfacing activity has predominantly utilised dense grade asphalts although more recently Stone Mastic Asphalt (SMA) has become popular especially where the existing pavement is heavily cracked. Roman II does not differentiate between types of asphalt surface and the use of SMA is a new treatment as well as still at a low proportion of all asphalts, consequently this paper does not differentiate between dense graded asphalts and stone mastic asphalts as a wear course.

Most of the metropolitan Perth Local Governments in Western Australia now utilise the Institute of Public Works Engineering Australasia/Australian Asphalt Pavement Association Technical Specification, Tender Form and Schedule for Supply and Laying of Hot Asphalt Road Surfacing for their asphalt paving works. The Specification includes mix designs with provision for stiffer bitumen eg class 320, and use of the specification has resulted in a very consistent quality of asphalt surface especially in the metropolitan area.

Climate

The climate in the South West of Western Australia plays a substantial part in the longevity of road pavements. The long term average maximum temperature in Perth is 24.7oC (76.5oF) and the average minimum temperature is 12.8oC (55oF). The average rainfall is 731mm (29 inches) over an average period of 104.9 days. There is no freeze‐thaw in Western Australia consequently the climate contributors to the aging of asphalt pavements are limited to the sun and rain.

Freeze‐thaw or frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedging and cryofracturing. The process may act on a wide range of spatial and temporal scales, from minutes to years and in the case of road pavements from accelerating surface raveling to splitting entire pavements. Frost weathering is mainly driven by the frequency and intensity of freeze‐thaw cycles and the properties of the materials subject to weathering.

The Local Government Association of South Australia has recently commissioned a comprehensive study by the National Climate Change Adaption Research Facility titled Quantifying the cost of climate change impacts on local government assets. The report includes predictions on the impact of climate change on Perth road pavements. The prediction is that in the year 2100 the average pavement life will increase as the average rainfall reduces.

Road Network

The key road network information for the participating Local Governments is included in Table 1 overleaf:

TABLE 1 Local Government Road Network Key Information

Asphalt Road Totals Length of Group Local Government Sealed 2 Area Reseal Percentage Road (km) Area (m ) 2 (m ) Resealed

Perth Coastal Group City of Belmont 229.28 220890 67350 30.49%

Town of Cottesloe 48.47 29120 22780 78.23%

City of Joondalup 1009.64 2627560 89785 3.42%

City of Melville 733.65 521344 189480 36.34%

City of Nedlands 147.00 131210 173290 132.07%

City of South Perth 197.77 193480 38250 19.77%

City of Wanneroo 1291.52 1028770 147140 14.30%

Murray Coastal Group City of Mandurah 667.16 441322 9140 2.07%

City of Rockingham 961.42 895201 46722 5.22%

Darling Range Group City of Armadale 683.66 549108 103567 18.86%

City of Gosnells 855.05 689125 147564 21.41%

Shire of Kalamunda 645.00 209450 100240 47.86%

Shire of Mundaring 602.75 129200 122970 95.18%

City of Swan 1306.97 691640 139117 20.11%

The data provides the following observations:

• The oldest Local Governments of Cottesloe and Nedlands (100 years) have resealed the greatest proportion of their road network with the City of Nedlands statistically having resealed every road in the network at least once. • The next group of cities that were developed such as Belmont and Melville (50 years) have resealed around a third of their roads. • The most recently developed cities such as Wanneroo (20 years) are only average 15%. • The was created in 1998 from the split up of the City of Wanneroo so it was fully developed but had no history hence the low resealing proportion of 3.42%. The annual Report on Local Government Road Assets and Expenditure published by the WALGA provides key performance indicators for pavement performance based on a financial model. The three key financial values are:

• Current Replacement Value ‐ is the current cost of replacing the road assets. It provides a datum from which the consumption of roads can be assessed. • Written Down Value ‐ is the current value after allowing for depreciation. The difference between replacement value and written down value represents the amount consumed. • Status Quo Cost ‐ is the estimated cost of maintaining the roads at their current condition. It provides a datum against which actual expenditure performance can be compared.

This paper considers two indicators based on the above financial values. The Road Condition Indicator is the ratio between the Written Down Value and the Current Replacement Value. The Preservation Performance Indicator is the ratio between the actual expenditure on preservation and the Status Quo Cost. These two key performance indicators for the road network since 2000‐2001 are demonstrated in the following two tables:

TABLE 2 Road Condition

Road Condition Group Local Government 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 Average Perth Coastal Group City of Belmont 0.65 0.66 0.66 0.66 0.65 0.65 0.66 0.66 0.75 0.75 0.76 0.76 0.69 Town of Cottesloe 0.67 0.65 0.65 0.65 0.65 0.64 0.65 0.67 0.64 0.64 0.56 0.56 0.64 City of Joondalup 0.79 0.81 0.81 0.81 0.81 0.81 0.80 0.70 0.65 0.65 0.68 0.69 0.75 City of Melville 0.69 0.68 0.67 0.67 0.67 0.67 0.68 0.66 0.56 0.56 0.58 0.58 0.64 City of Nedlands 0.67 0.65 0.65 0.65 0.65 0.65 0.66 0.66 0.64 0.64 0.54 0.54 0.63 City of South Perth 0.69 0.68 0.68 0.68 0.68 0.68 0.68 0.68 0.67 0.67 0.70 0.70 0.68 City of Wanneroo 0.75 0.74 0.74 0.74 0.73 0.73 0.74 0.71 0.77 0.77 0.79 0.79 0.75 Averages 0.70 0.70 0.69 0.69 0.69 0.69 0.70 0.68 0.67 0.67 0.66 0.66 0.68 Murray Coastal Group City of Mandurah 0.75 0.64 0.75 0.75 0.75 0.75 0.75 0.68 0.67 0.68 0.77 0.77 0.73 City of Rockingham 0.74 0.74 0.74 0.74 0.74 0.74 0.74 0.67 0.82 0.82 0.75 0.75 0.75 Averages 0.75 0.69 0.75 0.75 0.75 0.75 0.75 0.68 0.75 0.75 0.76 0.76 0.74 Darling Range Group City of Armadale 0.70 0.68 0.69 0.69 0.69 0.69 0.68 0.68 0.73 0.73 0.74 0.74 0.70 City of Gosnells 0.70 0.70 0.70 0.70 0.70 0.69 0.69 0.64 0.71 0.71 0.68 0.68 0.69 Shire of Kalamunda 0.71 0.69 0.70 0.70 0.70 0.69 0.69 0.68 0.72 0.72 0.72 0.72 0.70 Shire of Mundaring 0.70 0.70 0.70 0.70 0.70 0.70 0.69 0.60 0.60 0.60 0.62 0.62 0.66 City of Swan 0.71 0.70 0.69 0.69 0.70 0.69 0.68 0.64 0.62 0.63 0.68 0.68 0.68 Averages 0.70 0.69 0.70 0.70 0.70 0.69 0.69 0.65 0.68 0.68 0.69 0.69 0.69

The highest value recorded is 0.79 from the City of Wanneroo which is one of the fastest growing cities in Australia. The lowest value is 0.54 from the City of Nedlands which has some of the oldest pavements in Western Australia in excess of 100 years. The average indicator is around 0.70 which is generally identified as the preferred level for Road Condition in Western Australia. It can be therefore concluded that based on the data provided by WALGA, the average Road Condition in Perth is meeting the desired requirements at current intervention levels, that is the current average period of intervention is maintaining the required average quality pavement.

TABLE 3 Preservation Performance

Preservation Performance Group Local Government 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 Average Perth Coastal Group City of Belmont1.761.591.291.121.101.231.030.871.271.431.561.621.32 Town of Cottesloe1.662.382.482.261.751.941.641.881.771.731.671.791.91 City of Joondalup0.910.960.930.900.710.810.490.530.790.810.951.030.82 City of Melville 1.32 2.04 1.04 0.83 0.87 0.88 0.93 0.92 1.02 1.00 1.53 1.28 1.14 City of Nedlands 2.47 2.90 2.16 2.24 2.07 2.04 1.35 1.71 2.19 1.93 2.26 2.13 2.12 City of South Perth0.321.351.110.880.830.710.911.001.321.241.221.631.04 City of Wanneroo 0.68 0.70 0.66 0.63 0.60 0.44 0.55 0.58 0.48 0.47 0.57 0.49 0.57 Averages 1.30 1.70 1.38 1.27 1.13 1.15 0.99 1.07 1.26 1.23 1.39 1.42 1.28 Murray Coastal Group City of Mandurah 0.81 0.85 0.79 0.78 0.76 0.46 0.46 0.49 0.71 0.77 0.65 0.80 0.69 City of Rockingham 0.65 0.56 0.63 0.65 0.51 0.61 0.78 0.72 0.74 0.54 0.80 1.06 0.69 Averages 0.73 0.71 0.71 0.72 0.64 0.54 0.62 0.61 0.73 0.66 0.73 0.93 0.69 Darling Range Group City of Armadale 1.09 1.26 1.08 1.27 1.16 0.97 1.01 0.85 0.97 0.88 0.52 0.73 0.98 City of Gosnells 0.46 0.85 0.78 0.90 0.57 0.69 0.61 0.58 0.81 0.96 0.91 0.84 0.75 Shire of Kalamunda0.670.710.800.720.720.530.720.830.560.620.600.420.66 Shire of Mundaring0.921.020.880.830.780.650.680.730.910.850.710.870.82 City of Swan 0.87 0.72 0.83 0.88 1.07 0.92 1.04 1.02 0.90 0.90 1.05 1.31 0.96 Averages 0.80 0.91 0.87 0.92 0.86 0.75 0.81 0.80 0.83 0.84 0.76 0.83 0.83

One of the main drivers of the report is to encourage Local Government to spend the appropriate funds to maintain the road network. The preservation performance indicator establishes how much has been expended in comparison to the theoretical expenditure required to maintain the status quo. It can be seen that fully developed Local Governments such as Nedlands, Cottesloe and Belmont are required to spend more of their own funds to maintain the road network to the required condition than developing Local Governments who have the benefit of a relatively new road network heavily subsidised by developer.

The final Table from the report and on the slide provides annual expenditure per linear kilometre in built up areas, that is, the roads which have most likely been asphalted.

TABLE 4 Expenditure per lane kilometre in built up areas

Expenditure per Lane Km in $,000s (Built up Areas) Group Local Government 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 Average Perth Coastal Group City of Belmont $13,730 $13,165 $10,105 $8,966 $8,933 $11,033 $9,907 $9,240 $10,242 $11,524 $12,019 $13,663 $11,044 Town of Cottesloe $9,715 $14,175 $15,164 $14,129 $11,244 $15,668 $14,142 $17,474 $13,838 $13,533 $12,738 $14,866 $13,891 City of Joondalup $3,604 $4,338 $4,227 $4,168 $3,359 $4,253 $2,750 $3,167 $6,000 $6,124 $6,859 $8,189 $4,753 City of Melville $5,243 $8,420 $4,854 $3,982 $4,237 $4,729 $5,313 $5,628 $7,765 $7,545 $11,212 $10,158 $6,591 City of Nedlands $13,729 $16,314 $13,522 $14,355 $13,600 $15,335 $11,031 $14,689 $16,184 $14,146 $16,096 $16,346 $14,612 City of South Perth $1,910 $8,200 $7,584 $6,163 $5,966 $5,610 $7,777 $9,152 $10,518 $9,934 $9,387 $13,673 $7,990 City of Wanneroo $2,152 $2,234 $2,330 $1,557 $2,004 $1,652 $2,275 $2,948 $3,023 $3,140 $3,484 $3,328 $2,511 Averages $7,155 $9,549 $8,255 $7,617 $7,049 $8,326 $7,599 $8,900 $9,653 $9,421 $10,256 $11,460 $8,770 Murray Coastal Group City of Mandurah $3,565 $4,572 $4,733 $3,528 $3,986 $3,572 $2,260 $3,000 $4,920 $5,546 $5,134 $6,753 $4,297 City of Rockingham $3,241 $2,965 $3,351 $3,928 $3,229 $3,301 $4,135 $4,955 $5,167 $4,325 $6,571 $9,044 $4,518 Averages $3,403 $3,769 $4,042 $3,728 $3,608 $3,437 $3,198 $3,978 $5,044 $4,936 $5,853 $7,899 $4,408 Darling Range Group City of Armadale $4,946 $7,307 $6,076 $7,078 $7,221 $6,803 $6,274 $7,127 $9,389 $7,882 $4,615 $5,476 $6,683 City of Gosnells $2,614 $5,456 $5,165 $6,655 $4,375 $5,873 $5,857 $5,685 $6,725 $6,518 $7,495 $7,405 $5,819 Shire of Kalamunda $3,734 $3,473 $5,170 $3,552 $4,922 $3,341 $5,892 $5,650 $3,020 $5,129 $4,021 $3,738 $4,304 Shire of Mundaring $4,160 $3,924 $3,478 $4,941 $2,951 $3,756 $3,555 $4,832 $6,602 $5,639 $5,952 $4,261 $4,504 City of Swan $3,547 $3,598 $4,528 $4,993 $5,597 $5,141 $7,977 $6,534 $3,023 $7,217 $9,130 $11,510 $6,066 Averages $3,800 $4,752 $4,883 $5,444 $5,013 $4,983 $5,911 $5,966 $5,752 $6,477 $6,243 $6,478 $5,475

The fully developed Local Governments such as Cottesloe spends nearly $15,000 per Km which is 79% more than the Status Quo Cost and this only maintains a Road Condition of 0.56 which has been in decline over many years. The developing Local Governments such as Wanneroo spends around $3,300 per Km and is 51% under the Status Quo Cost but maintains a Road Condition of 0.79 because there are so many new housing and commercial developments funded by the private sector. Both Local Governments maintain similar levels of service.

The only other factor that would contribute is economies of scale because Cottesloe is a small single suburb Local Government with a population of 8,300 and Wanneroo is a rapidly growing City with a population of 173,000.

Deterioration Models

The average resurfacing periods generated from the Roman II data are presented in Table below:

TABLE 5 Average Resurfacing Periods

Length of Sealed Road Resurfacing Group Local Government (km) Period

Perth Coastal Group City of Belmont 229.28 13.4 Town of Cottesloe 48.47 27.5 City of Joondalup 1009.64 24.0 City of Melville 733.65 16.7 City of Nedlands 147.00 17.1 City of South Perth 197.77 11.0 City of Wanneroo 1291.52 20.9 Average resurfacing period 18.7 Murray Coastal City of Mandurah 667.16 26.3 Group City of Rockingham 961.42 13.2 Average resurfacing period 19.8 Darling Range Group City of Armadale 683.66 19.0 City of Gosnells 855.05 17.0 Shire of Kalamunda 645.00 14.3 Shire of Mundaring 602.75 22.8 City of Swan 1306.97 19.5 Average resurfacing period 18.5

The data has provided indications of the typical life of thin asphalts on the Swan Coastal Plain. The average resurfacing period for any Local Government has varied from as low as 11.0 years to as high as 27.5 years. The Perth Coastal Group with its pavements constructed on sand has an average of 18.7 years, the Darling Range Group at 18.5 years and the Murray Coastal Group at 19.8 years.

It is interesting that the groups have relatively consistent periods of resurfacing between 18.5 and 19.8 years with Murray Coastal Group the longest at 19.8 years. It could be surmised that the sub‐grade only plays a small part in the deterioration of the pavement, that is even the poorer soils are still of a good road building quality and they all benefit from a Mediterranean climate and no freeze/thaw.

ARRB Research

Between 2003 and 2007 ARRB conducted a series of field tests on pavements in Western Australia. The results generally identified that there was a slow deterioration of the pavement and the pavements were structurally appropriate in general. The surface criteria included cracking, roughness and rut depth. This study will only consider roughness and rut depth as these are consistent criteria across all pavements. There are three specific road sections within the ARRB research that have been included in this paper and these are included in the following Table 6:

TABLE 6 ARRB Roughness and Rutting Results

2003 2005 2007 Local Last Rut Rut Rut Road Name Roughness Roughness Roughness Government Seal Depth Depth Depth Lilburne Road Joondalup 1984 1.88 2.66 2.09 3.14 2.24 3.52 Vincent Street Nedlands 2002 1.66 0.89 1.59 1.01 2.04 1.23 Morrison Road Swan 1994 1.29 1.49 1.30 2.27 1.34 3.17

In general terms both the roughness counts and rut depths have gradually increased over the four year period. Discussions with road practitioners has identified that the ravelling pavement criteria is the most utilised criteria in the decision process to resurface a pavement.

Conclusions

The initial research indicates that road construction conditions in terms of quality sub‐grades and a Mediterranean climate on the Swan Coastal Plain are conducive to long lasting pavements. The research has provided an actual average resurfacing period of 19 years which has maintained a favourable road condition. We have also established that the available data sets are of good quality providing long term data for road pavements in metropolitan Perth.

Acknowledgements

The author wishes to thank the staff of the participating Local Governments, the Australian Road Research Board and the Western Australian Local Government Association for their contribution to date. The research could not take place without the support of Curtin University and my employer, Roads2000 Pty Ltd.