Dennis Polhill

By Dennis Polhill

Mr. Polhill is a civil engineer, served in city government for 10 years, and is currently president of Pavement Management Systems. Inc.

Three trillion dollars is needed to restore the nation’s infrastructure. ‘Infrastructure’ is all of the physical public works facilities which support the way of life, standard of living and economic vitality which the U.S. has come to enjoy.

During the past several years, the rate of investment in public works has declined by 4 percent per year. From 1965 to 1977, federal, state and local infrastructure expenditures decreased by a total of 44 percent. During the same time, construction costs rose at twice the rate of the Consumer Price Index to the point that two-thirds of the local governments in the U.S. now are unable to afford the facilities necessary to accommodate growth.

Best estimates of the nationwide cost of bringing our infrastructure up to standard are in the $3 trillion range.

Although the infrastructure challenge is national in scope, solutions to the problem will have to be found at the local level, in individual cities. In this connection, every city should develop an action plan which includes:

1. An inventory to determine the present condition of facilities and rank needs on the basis of objective criteria.
2. A financing plan under which sufficient resources will be provided to address identified needs.
3. An implementation plan which ensures that resources are utilized efficiently.

The most significant investment of cities is in their streets. Streets are more valuable, contribute more direct benefit to economic efficiency, and have a higher cost of replacement than most other facilities. Citizens are also more aware of the condition of streets than of other public works. Research has shown that the performance qualities of streets decline as the pavement ages, as illustrated in Figure One. Differing pavement structures, soil and environmental conditions, traffic loads and maintenance practices affect the shape of the curve in the illustration. Conceptually, however, the curve is always the same: the older the pavement becomes, the more rapidly it deteriorates and the more it costs to repair.

The process of inventorying and evaluating pavement systems is complicated because several factors are important, including strength, roughness, surface distress, skid resistance and rutting. Cities obviously are interested in maximum service as measured by all of these factors, but under economic restraints as they exist today cost is an overriding concern.

Scientific methods are now available for inventorying and making pavement decisions that can result in enormous cost savings.

To illustrate the cost significance of various street rehabilitation alternatives, take the typical overlay decision, which involves a myriad of considerations affecting cost and performance: (1) how thick should the overlay be?; (2) when should it be placed?; (3) when will the next overlay be required?; (4) what materials should be used?; (5) what alternatives to overlay are available and viable (recycle, fabrics, etc.)?

Concerning the thickness decision, too-thin overlay will fail prematurely, while too-thick overlay will cost more money than is necessary. Asphalt concrete costs about $40 per ton in-place, which is about $63,000 per two-lane mile for a 2″ thickness. If a 1 3/4″ thickness would serve as well, $8,000 per mile could be saved.

On the other hand, if a 2″ thickness would extend the serviceable life of the roadway by eight years and a 2 1/4″ thickness would extend its life by 16 years, trying to save the 1/4″ (or $8,000) would cost the city $55,000 in eight years, plus an accelerated reconstruction schedule to restore the crown and curb height.

Decisions concerning the best treatment for a specific street must, of course, take into account the needs o( the entire street network. In other words, optimum treatment “X” may result in 10 units of benefit for each dollar expended on Elm Street, but what about Main Street, where the optimum treatment may yield 12 units of benefit for the same expenditure of dollars?

Figure Two shows how maintenance costs increase over time, as the serviceability level of the street moves closer and closer to a minimum acceptable level. The end result is that a lower level of service is maintained at a higher cost than if rehabilitation was programmed at an optimum time.

This phenomenon has been verified by several studies, one of which was conducted by the Utah Department of Transportation. As shown in Figure Three, the Department found that the most cost-effective strategy for maintaining urban streets and the one which sustained the highest serviceability level involved timely rehabilitation activities performed during a comparatively short time frame: The most costly approach shown as “Strategy C” in Figure One was one under which rehabilitation was delayed until public pressure forced action to upgrade serviceability to minimum acceptable levels.

In summary, it is apparent that the extent of deterioration of streets and other public works is enormous – and growing -due to past policies of deferring needed maintenance. The problem can, however, be solved if local governments will inventory their needs and then adopt plans to finance those needs.

With specific respect to streets, research has demonstrated the correlation between varying maintenance levels and pavement serviceability. Proper management of maintenance activities can produce high levels of serviceability at minimum cost.

Reprinted from the January, 1983 issue of Colorado Magazine.