PUBLIC WORKS MAGAZINE, April 1987
DENNIS POLHILL, P.E.
Mr. Polhill is vice president of Pavement Management Systems, Denver, Colorado.
Pavement management has become a familiar concept among public works managers, and each year more public agencies develop a structured program. It is important that technical issues be discussed among public works professionals so that a common understanding of such systems can be developed. To adopt a system without a clear understanding of the possible options can result in expenditures that are not as cost-effective as desired.
The benefits of pavement management can be substantial. At the design or project level the benefits of using the latest and best information available fall into two categories:
· Immediate savings in construction cost by not building over-designed facilities.
· Long term cost savings in the form of reduced future maintenance costs by preventing “under-designed” structures.
Assigning a dollar figure to future maintenance costs is difficult because some service is provided up until the time of premature failure and repair. A further complication is the inflation of construction costs and the discounting of dollars to present value. However, investing in information acquisition on which to base a design can easily be recouped in construction and maintenance savings. Even relatively small cities have reported savings ranging from $20,000 to $250,000; and in several cases the return on the investment has been more than 5,000 percent.
Rehabilitation and Timing
At the design level the focus is on determining the most appropriate rehabilitation. At the network level the focus is on timing. Many communities and agencies have implemented network level pavement management systems. But the questions to be asked include: Are these systems worthwhile? Do they generate savings? Are the savings significant?
At the network level agencies are interested in a reasonably accurate method of predicting pavement performance. A reliable and useful prediction model will determine both the best timing as well as the funding level required for rehabilitation. It is not practical from a cost standpoint to collect all the data needed for detailed engineering design of the rehabilitation for an entire network. Network level pavement management is a management tool while design level pavement management is an engineering tool.
To determine the benefits of a network system it is necessary to know future funding levels and to have a knowledge of how the funds will be expended. This forms a baseline for future comparisons.
Both politically motivated public works management and simplistic pavement management systems that operate without the benefit of structural strength data tend to establish priorities on a “worst-first” basis. Under this approach, however, the needs can quickly outstrip available funding. As the road surfaces become more and more deteriorated the rehabilitation options become fewer and the associated costs higher. The required funding level can grow exponentially. Often the streets deteriorate to a point where the governing agency makes a massive funding effort to correct the problems. Unfortunately because of the crisis atmosphere generated by the hasty attempts to catch up with the deterioration, the funding is often not used cost-effectively. But because the “worst-first” mentality prevails, the solution is short lived.
Changing this philosophy requires the use of modern pavement management techniques that accurately evaluate the benefits of different options. Municipalities that have benefited from such a program include Ottawa-Carleton, Ontario, a 14 percent reduction in its street budget; Thermopolis, Wyoming, 16 percent reduction in street budget; and Hartland, Wisconsin, a 24 percent budget reduction. Waterloo, Ontario saved 107 times the cost of the system in four years. Figure 1 illustrates conceptually the impact on the backlog of needs after implementing a management system.
Expenditure of funds is based on cost/benefit calculations for each rehabilitation strategy employed. Establishing priorities based on assessment of the incremental cost/benefit calculations produces the maximum use of available funds and makes candidate projects compete with each other for priority. The projects that yield the greatest rate of return are chosen. The technique of setting priorities by minimizing costs and maximizing benefits is called optimization. (Cutting off the bottom of the “worst-first” list is not optimization.)
Examining the street funding power curve shown in Figure 2 illustrates the following:
· The y-ordinate represents the total needs backlog at any point in time.
· Many highway agencies have a backlog of needs that grows exponentially.
· Funding the backlog of needs is very difficult if not impossible.
· If currently available funds are used more efficiently, the future needs backlog can he reduced.
On Figure 2, I is the point in time when the management system was put in place and S represents the point where the backlog of needs stops growing. To some observers during the time frame between I and S it may appear that pavement management is not working. The y-ordinate value represented by the difference of Y2 and Y1 is the benefit of the pavement management program. Close to point I the benefit is small, but as the two curves diverge the benefit becomes substantial. The point N represents the time where there is no backlog. When this is reached the governing agency can make some major policy decisions: Should budgets be reduced? Should the street quality standard be increased? Should funds be redirected to other municipal service areas?
Governing bodies usually feel more comfortable in providing increased funding for streets after a pavement management program is in place since the expenditures can be readily justified. In Figure 3 two funding levels are shown — a high funding level marked as curve 1 and a lower funding level noted as curve 2. Many management systems work in different ways and may have different levels of efficiency.
Sometimes it is necessary to phase the implementation of a pavement management system. Phasing can be either vertical or horizontal. Vertical phasing is the implementation of a system over part of the network. Horizontal phasing is the implementation of a partial system over an entire network. In Figure 3, curve 2 may represent the first phase in a horizontal or vertical plan while curve 1 may represent a system that is not phased.
The commitment of top management can also affect the success of the management system. While it is sometimes important to deviate from a specified plan of action, it should be realized that the variables introduced from the deviation will require certain trade-offs, which may have some long term effects. Thus in Figure 3, curve 2 may represent a greater degree of “tinkering” with the system than is represented by curve 1.
Many public works managers must work with programs that are underfunded. A proper pavement management system may help some agencies reduce yearly budgets, but will not help those whose expenditures are already inadequate. If the funding level is too low or the backlog of work too large even the most efficient use of funds may not be enough to overcome a growing backlog of needs.
The benefits of pavement management systems can be substantial; savings can be many times the initial investment for engineering data. A good pavement management system will provide benefits that increase with time. These benefits become greater as the needs backlog curves diverge from one another.