PhD School of Business and Public Administration
University of the Pacific
MPW Pavement Management Systems Denver
the 1990 Regional IX Conference of the American Society for Public Administration Honolulu, Hawaii
October 8, 1990
For submission to
the Journal Public Productivity and Management Review
The objective of this research is to examine methods for public works maintenance investment decisions. Beyond initial capital choices using benefit-cost analysis, this paper explores performance measures to observe the physical condition and performance levels over the life of infrastructure systems. Given adequate information, alternative investment policies or maintenance strategies (prevention, rehabilitation and reconstruction) can be compared using performance levels and costs.
A general approach is presented for examining infrastructure systems and maintenance investment choices, with an example drawn from pavements. A discussion of the analytical process of maintenance management systems is provided in terms of required information, decision rules and optimization models Since public works managers are inundated by consultants with computer packages purporting to assist with infrastructure policy making, this article provides managers with a basis for criticizing maintenance management packages and their role in investment decisions.
Infrastructure Maintenance Investment: Beyond the Benefit-Cost Analysis
Today the word infrastructure is the popular usage for what has been known for most of our history as public works. While these two terms can be used interchangeably, conceptually a distinction will be drawn between infrastructure as the physical
platforms used to serve our communities and public works as the public agencies which own and deliver services at all three levels of governments. Infrastructure systems are normally owned by public agencies, often operated as public enterprises with
some degree of independence from parent governments. A portion of these systems are owned and/or operated privately, some water and transit agencies and almost all electrical distribution even though power systems are also provided by federal or local
Examples of these physical infrastructure systems include:
- Highways, streets, sidewalks, lighting and curbs and gutters
- Water resource systems, water supply and sewage treatment
- Flood control systems, storm drains, channels and dams
- Solid waste systems, collection and disposal resources
- Transport systems, airports, seaports, mass transit, and tunnels
- Public buildings, grounds and parks
- Equipment, vehicles, pumps, treatment facilities
- Electrical, natural gas and telecommunication networks
These are systems that are widely available to the general public, although similar systems are developed by the military and many private industries on their own property and at their production plants and facilities. the focus here are those public works wholly owned by governments and planned, delivered and financed through public institutions.
Public works has historical connotations of public investment for the wrong reasons, that is “pork barrel” rewards by elected representatives to local constituents, for political tradeoffs among legislative members or as employment patronage. Such negative images of public works have clearly been overblown and have overshadowed the massive contribution that public works investment has provided for urban, regional and national growth, for the public health, safety and convenience.
The goal of this research is to focus on the management tasks of professional engineers and managers who deliver desirable and necessary public works platforms for commerce and public activity. The maintenance investment levels these managers recommend, not for the traditional capital decisions on new facilities, but for continuing repair, rehabilitation or reconstruction, are the policy decisions in question. These ought to be reviewed as economic investments decisions as is any infrastructure expenditure in the private sector.
Public works facilities have grown significantly during the last 40 years, with investment financed by local/state government debt, by federal/state grants to local agencies and by economic growth and general taxation of urban and suburban communities. This growth was strong during the period of 1950-1975, with almost all governments having the fiscal capacity to finance the infrastructure developments and adequately cope with maintenance burdens. Investment was justified by cheap debt, legal debt capacity, federal largesse and the ability of local/regional governments to realize increased property/sales tax revenue, sufficient to pay for debt retirement, the local share of capital costs and a lifetime of maintenance costs.
Now we are faced with a new reality, the results of drastic shifts in the environment of government. Economic stress caused by an oil crisis, massive inflation, unfathomable tax increases and a political reversal that found a welcome audience for a decreased role of the public sector in the lives of citizens. The impact on public works was a dual threat created by an aging infrastructure, some originally built 100 years ago, and a maintenance budget neglect stimulated by financial scarcity and deliberate cutbacks in the expenditures of governments in the 1970s and 1980s.(1)
Deferred maintenance is politically and physically acceptable because an immediate effect is not felt: Yet this neglect is insidious. As these facilities age they physically decay and provide less capacity and service to users and slowly but surely the public is faced with an increased risk of failure, delay, accident and injury. The stress of competing priorities has left public works agencies with “hypofunding” at exactly the wrong time in their life cycle.
Traditional Public Works Investment Decisions
While public works investment decisions are the choices of government leadership based on the recommendations of public works managers, political preferences as well as concepts of economics have impacted investment. Since the 1930s, investment decisions for new public works facilities have sought to base budgeting decisions on the technique of benefit-cost analysis. Considered by engineers, managers and legislators alike to be an appropriate method for comparing projects, benefit-cost has the neutral objective of maximizing the net payoff of benefits and costs that can be measured in dollars.
It is an intoxicating method, for the initial understanding of the analysis easily convinces one the investment decision that chooses the highest present value of the net cash flow is surely the most rational act for public decision making. Given the acceptability of the benefit-cost logic, the method has been mandated by some federal statutes for federal program projects as well as categorical/project grants to state/local governments. Of course, analysis of a flood control or transportation project does not always insure projects across all public works functions are compared or insist certain areas/regions be neglected if their benefit-cost ratios were low or less than one. Obviously, imbalances between highways and flood control development would not be practicable solely on the basis of the highest benefit-cost projects for all infrastructure, let alone other public programs. Government is not simply maximizing total wealth as a private enterprise would do, but instead it is required to Provide a set of infrastructure necessary for community life
whether or not the best investment return is realized. But given limited resources, the goal of economic rationality may become more desirable for public investment.
In spite of the inference above, it is not the intention of this paper to challenge the use of benefit-cost analysis in infrastructure capital development. None-the-less, there are
both strengths as well as potential in such economic analysis.(2)
Arguments that justify benefit-cost:
- Utility of benefits and costs are compared as dollars
- Time value of money is expressed by present values
- Discount rate is chosen as the best opportunity rate for alternative use of the resources
- Net present value calculations can compare projects and determine whether projects should be funded at all
In sum, the analysis can take the capriciousness out of decisions.
Dangers that decrease the value of benefit-cost, even create risk with its use:
- Benefits must be reduced to dollars, neglecting some utility that cannot be measured easily with dollars
- Benefit calculations are often implied and can be exaggerated
- Possible alternative actions are easily neglected
- Discount rates affect results of the analysis, slower rates can help justify investments
In sum, the analysis can be misused to support predetermined preferences.
Another issue in capital decisions is how maintenance costs and choices are included in the analysis of public works projects? Commonly an estimated cost for maintenance is included in the benefit-cost calculations over the life of the project. There is some doubt as to whether a serious understanding of maintenance burdens over the life of the facility is developed at the time the capital decision was made. More likely a simple estimate is developed with little thought of alternative maintenance strategies or alternative designs that affect maintenance requirements and costs over time.
In benefit-cost analysis, cost estimates are thought to be more accurate and honest than benefit data. Benefit measurements may well be implied or imputed and contain data which is often subjective and uncertain. For maintenance costs, inaccuracy and uncertainty may creep into the analysis because a serious exploration of the maintenance management task has not been attempted at the early stage of new facility development.
In spite of new infrastructure construction in may parts of the nation, for the most part of public works task is shifting from capital development to maintenance of a decaying infrastructure where planned useful lives of many facilities are being exceeded. As systems decay, capacities are decreased and failures become more frequent. The result is a public not able to finance the necessary rehabilitation to protect their interests and decrease their risks.
Infrastructure Management Today
A thoughtful essay prepared by Royce Hanson entitled “The Next Generation in the Management of Public Works” challenges us to recognize a generation of public works management where the “management of the capital stock will be more important than
adding to it.” He admonishes public works managers:
“Engineers and public works directors think of themselves as builders, not maintainers and managers. They live capital-intensive fantasy lives. Replacing the ‘edifice complex’ with a passion for management will require major changes in the education and acculturation of those who lead public works organization and those who educate them.”(3)
A premise of this research is that the task of maintenance management has not been well developed in the field of public works management. Hanson explains the maintenance immaturity as follows:
“Maintenance has fared poorly in public management for several reasons. There are no well-defined standards …it is hard to measure the impact of preventive and regular maintenance programs-construction has a strong constituency… maintenance has weak public support. The effects of poor maintenance are insidious but slow to become obvious… maintenance is usually supported from general operating revenues and must compete with other higher visibility services… it is, therefore, an easy budget item to cut or constrain …since the effects …are unlikely to show for several years.”(4)
Given this challenge, the purpose here is to comprehend the maintenance management task facing public works managers, to address the methods of analysis used by those at the cutting edge of maintenance technology and to prepare managers for the consultants trying to assist agencies with the management needs for more sophistication in infrastructure maintenance decisions.
Public Works managers have significant choices as they commit resources to maintenance of existing facilities. Several maintenance strategies are available and the management task is to determine which strategy should be applied with what frequency throughout the life of infrastructure systems. A simple set of alternative interventions is listed below, from routine and repetitive preventive maintenance to major and infrequent reconstruction:
- Preventive maintenance and inspection of facilities: cleaning, clearing, protecting
- Periodic repair of weaknesses or failures: patching, filling, correcting
- Rehabilitate or to refurbish: overlay, reline, or reapply
- Reconstruct part or all of the system: remove and reconstruct or replace
Managers normally rely on their past practices and intuition with these systems to decide which maintenance strategies are appropriate for each budget cycle. They are faced with political pressure to select particular segments of the infrastructure network for immediate attention, while they have a professional obligation to uniformly and fairly serve user needs. In either event they may not choose an optimal allocation of resources in economic terms or by any other performance standard. A simple economic analysis may not consider the actual utility of system performance to the jurisdiction, because such performance measures can go beyond dollar benefits to more elaborate measures of capacity/convenience, safety/injuries and strength/failure risk which are not easily measured in dollars.
If works managers seek a more sophisticated method, then a “maintenance management system” which includes a technical evaluation of infrastructure performance history, a prediction of system performance under different maintenance strategies and costs can allow a more optimal allocation of maintenance dollars. This does not mean managers’ intuitive should not enter the investment decisions. The collective experience, knowledge and judgment of public works maintenance manager can be captured via “expert systems” and used as input to investment decisions. The ultimate decision ought to be made after seeing the evidence of a maintenance management which can integrate an expert system into the analysis.
The following description captures the momentum of academics, consultants and practitioners who are already engaged in maintenance management systems.
Maintenance Management Systems(MMS)
Public works will need a maintenance management perspective to meld with a capital investment plan. Non-growth communities as well as those cities with aging infrastructure are increasingly obligated maintenance and rehabilitation. Royce Hanson suggests the opportunity for public works managers:
“Faced with less money to replace facilities, managers have begun to perfect their maintenance regimes …with the availability of analysis units, computers and other advanced technology, managers are moving from 2nd generation preventive maintenance programs, based on regular cycles of inspection to condition-based systems that can target maintenance efforts more precisely to areas of greatest need. A number of jurisdictions are also developing guidelines based on analysis of levels of risk to set work priorities and to improve on targeted systems”(5)
A comprehensive MMS allows questions to be fully and analytically examined. What is the best combination of alternative maintenance strategies? Does increased preventive maintenance decrease the frequency of periodic repair? Will more frequent rehabilitation extend the life of the facility and lower the life time cost to the owner? Are minimum performance standards being met regarding capacity, safety and structural integrity? What is the expenditure required each year to obtain the minimum life cycle cost for the desired system performance?
Given accurate initial costs, coupled with life cycle maintenance expenses, public works managers can provide rational recommendations for needed infrastructure investment.
Yet design choices also affect maintenance decisions. Decisions in the design process may reduce the overall maintenance cost or may suggest different maintenance
interventions than expected or traditionally performed by public works managers. It may be better to increase capital costs to save in the long term, defensible only with more elaborate analysis.
MMS goes beyond minimizing cost to include measurement of infrastructure system performance expected with maintenance intervention. Over the last decade an approach to maintenance management has evolved that replaces simple dollar measures of infrastructure benefits. A comprehensive measure of condition and performance can be chosen and observed over time. Engineering studies will predict performance decay rates under usage and maintenance choices. Analysis can then compare maintenance polices to maximize performance for a minimum cost or a predetermined budget.
The following procedure details a generic method for conducting a MMS. It can be applied to any infrastructure system, be it roadways, embankments/levees, channels, pipes,
buildings or equipment. A specific discussion of pavements will be introduced later since roadways have received the most frequent application of MMS methods to date.
A General Maintenance Management Procedure
- Assuming the physical system is in place, gather relevant information on its layout and characteristics. Also identify maintenance assumptions in design regarding expected life and planned usage.
- Define service parameters for any infrastructure system. Multiple variables can be chosen and integrated into a comprehensive effectiveness measure. Selected parameters may include capacity, comfort, safety and structural integrity. These variables should represent the utility of performance as preferred by the owner jurisdiction, influenced by professional standards. These performance measurers may evolve over time and may include more complex engineering analysis. Generally, an integrated performance measure will be a simple multiple attribute model as shown:PERFORMANCE INDEX = WiXiWhere Xi are parameters for quality of the service and Wi are weightings or coefficients chosen by the agency in concert with engineering analysis.
- Observe the current condition of the system in terms of the performance parameters. Ideally a history is available to help predict future performance with a particular maintenance strategy for the actual system under its unique environmental and usage conditions.
- If an agency’s own performance history is not available because they have not kept necessary records or have not tested their systems with alternative maintenance configurations, they must rely upon research studies which have tested comparable systems under similar environmental situations and demands.(6) Then engineering analysis allows a prediction of performance with different maintenance choices. A conceptual model for expected performance decay and maintenance interventions with minimum standards is demonstrated below:(7)
- Given the performance variables and the predicted performance of maintenance programs, it is possible to make choices as to maintenance investments in the short term and long term. The method of selecting projects or areas of your network for interventions can range from a simple ranking procedure to a complex optimization technique. A representation of this analytical continuum follows:
a) List all projects needed to achieve minimum acceptable performance levels and select by least cost or a heuristic criterion
b) Rank projects by total performance achieved over time (area under performance curve) and accept all those within the budget
c) Rank cost effectiveness or total performance area divided by cost for all projects and select within budget limits
d) Select optimal combination of projects based on performance area and costs, using a mathematical model
- Implement the desired investment policy over several years through a work scheduling and control system. Establish an information system to record data on the resources expended on maintenance projects (actual costs of equipment, labor and materials), including productivity data. Conduct surveys on facility condition to verify predicted performance. This validation step also provides information to revise the methodology in subsequent years.
Applying Maintenance Management to Pavements
Pavements are a common usage of MMS because they exist everywhere, in highways, bridges, streets, airports/seaports and parking lots. Pavements represent a large portion of public works investment than any other pubic facility. Pavements provide direct, immediate economic benefit to the concern unity, thus they receive the fist and most attention.
It is relatively easily to observe and feel the physical conditions of pavements and the public may demand quick fixes to the potholes, cracks and rough surfaces. Many research and professional organizations have done much on pavement maintenance strategies but this research has received minimal development and application. Public works mangers need to learn how to put these ideas and research results into practice.(8)
To begin a pavement management system(PMS) the search for performance measure is the initial step. The research have established a very similar integrated performance measure or present serviceability index(PSI).(9) This approach integrates several parameters into an overall performance measure. For instance:
PSI = f(riding comfort, skid resistance, structural strength, visual condition)
Riding quality or comfort had correlate well with PSI according to AASHO highway research.(10)
These individual parameters can be weighted according to the choice of agency. To some managers the strength parameter is more important to their decision making.
On the bases of engineering research pavement serviceability can be related to technical design measurements. Without presenting the precision mathematical expression, the following function has been developed empirically:(11)
PSI = f(pavement structure, regional climate factor, soil support value, number of design axle loads)
Agencies must find the commitment to observe the chosen parameters over the usage history of their pavements. While this is a task they ought to be able to conduct themselves, most will need to be trained. Some smaller communities may continually need assistance.(12)
Predicting performance of a pavement under environmental conditions and usage is essential, yet by far the most technically demanding part of PMS. It is beyond this paper to capture the engineering research and analysis involved in establishing the relationship with pavement overlays, patching, seal coating or reconstruction and the expected performance over time after maintenance actions. This is a critical part of this method and will depend on an engineering analysis and past research results. Significant research has been conducted and agencies, together with consultants in PMS, will need to rely on the work of the Army Corps of Engineering and the American Association of State Highway and Transportation Officials.(13)
To help comprehend the analysis involved in pavement management investment choices, a simplified example from the book by Haas and Hudson is presented.(14) Performance curves and cost calculations are shown on the figures which follow. The example proposes 3 alternative rehabilitation strategies, essentially using different pavement overlay thickness. The performance profiles in the first figure displays the rates of performance decay expected, which would be based on surveys and research information.
In this example the utility of serviceability has been converted to reduced costs to users. These benefits or cost savings are different for the 3 alternative strategies. This approach requires the agency or their consultant to convert improvements to reduced costs. But the credibility of this conversion remains questionable and further work must be done to develop adequate information to convince managers and political leadership. All agency and user costs are then discounted to present values, very much like a benefit-cost approach. While the figures demonstrate the cost analysis, the risk of faulty calculations of user costs remains.A preferred approach because of the weakness of benefit or cost savings calculation would not assign dollar values to pavement performance but would maximize the level of PSI over the life of the facility, choosing the strategy with the largest area under the PSI curve.(15)
In this case, the objective would be the maximum performance for the minimum cost over some period of time. This could be achieved analytically by ranked comparison of the performance-cost ratios for a finite number of alternative maintenance treatments within a given budget: A more elaborate approach could use an optimization model like linear programming to provide the maximum performance for a mix of projects within a budget constraint or another version of a LP model would minimize total cost over time, constrained by required minimum serviceability levels across part of all of the network.
Choices for conducting a PMS and its required engineering studies and management analyses are the responsibility of the public works manager. Before making a budget recommendation, each manager ought to comprehend methods, data requirements, performance variables, research inputs and determine the staff and computer resources needed to complete the process.
Critical Questions for Maintenance System Managers
From the perspective of the public works manager, several questions and related policy issues are addressed. The following arguments are ordered according to the generic MM procedure introduced before.
- How is the agency’s infrastructure system performance being measured? Let it be a conscious choice of the management and not simply an acceptance of an engineering text or computer program. Of course, for any performance measures chosen, it must be possible to relate maintenance strategies and to decay of the system serviceability over time.
- Historical records of infrastructure systems provide a necessary start toward understanding MMS and achieving an analysis which is rational. Given the technical sophistication and an era of privatization, most will need to hire a consultant to survey systems, train staff and conduct analysis. While taking advantage of the consultant’s experience, can public works agencies develop the internal skills to gather information, comprehend the approach and the analysis and build the computer data bases needed?
- Since the most difficult part of the process in the determination of performance decay rates for systems under different maintenance applications, most agencies will need to rely on research of others and use consultants to develop these relationships. Managers can become technical critics at this stage, using their engineering and administrative staff to insure understanding and prevent domination by technicians and consultants.
- Decisions about the economic or analytical methods used to finally choose a set of maintenance projects is the burden of public works managers. In reality, many agencies will choose a simple ranking of projects by cost, possibly with some heuristic rule for selecting projects within the budget constraint. A simple approach results for a variety of reasons. First simplicity readily allows political input: second, managers may not understand the methods: third, data availability may limited analysis and, finally, the cost of elaborate analysis is often unacceptable? Managers need to recognize their obligation to choose the method used to select projects when they enter into an agreement with a consultant.
- Project cost control is always desirable for budget responsibility, but a valuable payoff of a comprehensive cost accounting record goes beyond fiduciary control. Such data is essential to provide information to validate MMS decisions. Were the costs predicted in design or in the maintenance decision stage accurate? This same control system can include observation of infrastructure facility serviceability, also critical to validation of the MMS methodology.
An Inundation of Consultants
At every turn, public works managers have opportunities to acquire a consultant’s service to assist them with a MMS, for almost every infrastructure system they manage. The APWA package called PAVER can be an alternative to consultants. (16) During the preparation of this article, MMS consultants contacted were quite hesitant to share information about their methods and computer packages. They do consider the information proprietary and welcome the purchase of services to get access to their computer program.
An argument for open sharing of computer packages is not being made. Since most public works organizations could not accomplish maintenance management without consultant assistance, the availability of consultant services and their price will affect usage. Since wider use is encouraged, some means need to be developed to distribute the potential of MMS to the broader public works community at a reasonable cost. Hopefully, this manuscript will contribute to that end.
Nonetheless, there are some issues to be raised as practitioners are considering consultant packages. Managers who consider consultant services are acquiring both a method of determining maintenance investment, as well as a computer package for handling data, conducting analysis and producing reports.
To begin, any computer package ought to be judged by at least these criteria:
- What hardware storage capacity and processing speed is needed?
- How does the program interface or network with existing information systems and formats in your organization?
- Is the program user friendly, does it contain menus for clear options and ease of execution?
- Is the personnel training required kept to a minimum, are manuals available?
- Is technical assistance readily available and at what cost?
- Does the program accomplish the needed tasks you had predetermined?
As important as these initial questions, there are further issues managers face with MMS:
- onsidering the balance between the agency’s own efforts and those of the consultant, can the agency minimize costs with certain tasks completed by agency staff? Field testing, data collection and even report generation may be done in house, serving to increase the knowledge of the agency and reduce costs.
- Can the agency adapt the program to fit special needs and existing information systems? It is acceptable if the agency’s present project, work schedule and cost accounting record systems must be recreated in the format of the consultants’ computer package?
- Are there options used for comparing performance and costs when selecting maintenance strategies and work projects? This critical part of maintenance investment recommendations is often not considered seriously by public works managers.
It is not expected that all agencies and computer packages will achieve sophisticated methods of analysis. While there may be little additional payoff compared to less sophisticated methods, even a small marginal benefit can save millions of dollars over the life of these expensive capital projects. Also the cost rises when computer packages are more complex and demand better hardware capacity, speed and processing. Many users of computer services are not ready to comprehend high sophistication in analysis, so there is a tendency by managers and consultants alike to choose a method that is understandable by all actors in the policy making process. The goal of optimality in maintenance investment decision making remains an issue to be recognized by managers as they embark on a MMS.
In general, a consultant can do it all for you. For most agencies, asking the above questions will cause them to take actions to save consulting dollars and enhance their ability to
eventually more of the work themselves.
Conclusion and Opportunities
MMS provides a focus on infrastructure and public works management at the right time and brings the right solution to a national problem. With aging facilities and maintenance neglect, public managers have the opportunity to address the political lethargy. If they develop management systems, gather data, conduct analyses, they can offer public works investment recommendations that convincingly argue for getting beyond the infrastructure crisis.
No other path seems possible: that is, in absence of the management methods presented here, no progress on infrastructure seems likely and the public will continue to be placed at increasing risk when using our public works. More use of private consultants will likely result in acceleration of change and technological innovation in public works.
MMS have been installed by many communities in this nation whose managers have been willing to pursue an innovative approach. The large number of consultants could not survive if many public works managers were not taking the leap. How these managers are actually using MMS should be the focus of substantial research by all academics concerned with infrastructure as well as APWA, the professional association of public works managers. Civil engineering and public management disciplines ought to join together to raise the national consciousness about infrastructure condition and the methods and criteria used to make these public policy decisions.(17)
No doubt there will not be sufficient funds forthcoming to bring infrastructure conditions up to ideal standards any time some. Therefore, it is even more critical that the best decision models are available to the policy process to seek the maximum performance for limited dollars and to create the most convincing case in this national political neglect.
There has been much written to suggest new institutional, financial and managerial innovations to address the infrastructure issue. This presentation offers an approach, an innovation for many public works organizations, that can improve public policy making without demanding significant additional workers or management resources. No new administrative units, no structural change in government or new legislation is proposed. Rather the message is simply concerned with the managerial method of making budget recommendations for public works maintenance expenditures.
None-the-less, this approach to maintenance management may surface the need for increased budget dollars to achieve the minimum standard of infrastructure performance, let alone to achieve the optimal long term performance-cost. In addition, this analysis of total life cycle costs will suggest the need to reconsider design standards and assumptions. It will focus managers and policy makers on the main policy issues and make the need for infrastructure investment more manageable. Whether or not increased funding is received in the short term to begin to overcome weak performance, all this research asks is that the condition of infrastructure and the consequences of investment be made clear and open to public debate.
- Pat Choate-and Susan Walter, America in Ruins, Council of Planning Agencies, 1981
- See the critique of benefit-cost in “The Economics of Planning and Managing Public Investments”, Ch.4, Vaughn and Pollard, Rebuilding America, Vol. 1, 1984
- Royce Hanson, The Next Generation in the Management of Public Works, National Academy of Public Administration, Washington DC, November 4, 1987, p. 40
- Ibid, p. 21
- Ibid, p. 26
- AASHO (AASHTO)
- Ralph Haas and W. Ronald Hudson, Pavement Management Systems, Krieger, 1978, p. 264
- TRB, NSF, FHWA, NCHRP, State DOTS and APWA . . . .(PAVER)
- Ibid: and Pavement Management Guide, Roads and Transportation Association of Canada, 1977
- AASHO tests at UI
- Hass, p. 76 R. Yoder and Witsak, Principles of Pavement Design, John Wiley, NY, 2nd edition, p. 508
- Haas and Hudson, p. 51
- AASHO Road Test etc.
- Ibid, pp. 223-226
- Pavement Management Guide, p. 3.14
- Contact the American Public Works Association’s Research Foundation, Chicago, for information on PAVER
- A network of public works management academics have been formed, including faculty from eleven graduate programs in Public Works management recognized by the American Public Works Association. One author, Willard Price, chairs the network. See Graduate Education in Public Works Management: Comparing Recognized Programs, addressing the Maturation of the Field, a report to the American Public Works Association, Graduate Education Committee, September 1990, by Willard Price.