It is important to understand the history of pavement management in order to educate and elevate the process of pavement management. Let’s review how pavement management systems came into being.
In 1965, the National Cooperative Highway Research Program issued the best Request for Proposals I have ever responded to. It basically said something like this:
FHWA and State DOTs have been building interstate highways for about 10 years which are intended to last 30 – 50 years but 30 to 40% of them are failing in less than 10 years. What is the problem? We want a research team to find out why the failures are happening and propose a solution.
I was honored to be part of an outstanding team that included Fred Finn, Dr. Frank McCullough, and a great support team that was selected to undertake this study. We reviewed all interstate design and construction procedures; none seemed to have major problems. Then we convened a group of 20 of the best known flexible and rigid pavement engineers and outside experts in the USA for five days, breaking into small groups to discuss maintenance, construction, and design separately and then meeting as a whole to discuss and exchange notes. After these intense meetings, it became clear that too much emphasis was being given to “design” for the interstate highway system and for other primary highways and not nearly adequate attention to construction, maintenance, and rehabilitation. The project team turned its attention to discussing the interaction of design, construction, maintenance, and rehabilitation. Dr. Karl Pister, Dean of Engineering at the University of California at Berkley, pointed out that we had a very complex expensive problem with thousands of miles of heavy-duty pavements and that we needed to “systematize” this problem. Based on his systems engineering experience in the US space program, he outlined a simple input/output diagram for a pavement management “system.” (1)
Our project research team took these ideas and studied this input/output diagram, worked on it and obtained all the system’s engineering literature we could find. Over the next six months pavement management systems (PMS) were born and the very first PMS was developed and programed as an operational pavement systems model called SAMP (Systems Analysis Method for Pavements) (1). Dr. Ralph Haas and a team in Canada at the University of Waterloo had more or less come to the same conclusion and Dr. Haas and I soon formed a partnership and wrote the first book on pavement management in 1978. (2)
After several years of development and familiarization with PMS, many planners and DOT managers recognized the need to coordinate not just a single project but also a network of projects to help their agency allocate pavement budgets and provide the most overall benefits in terms of pavement performance and condition for their total network; or conversely to determine the short fall expected with existing budgets. Network level PMS thus has been the primary focus of pavement management for the last 30 years.
Yet AASHTO has spent nearly $30 million over the last 10 years to develop the Mechanistic Empirical Pavement Design Method (MEPDG). This method requires 350 design variables for flexible pavements and over 100 variables for rigid pavements. However, what is the likelihood of predicting the future value of each of 350 variables if each value can only be predicted with 95% accuracy, (which is higher than can really be expected with so many complex variables)? The probability of predicting the correct value for all 10 variables in a design problem is 0.60. The probability of predicting correctly with 100 variables is about 0.006 or practically nil.
PMS was developed precisely because agencies had shown that they were unable to predict correctly even the five or six basic design variables for pavements thus pavements did not perform as predicted. When errors in prediction occur and performance differs from that predicted it is possible to use PMS to make adjustments, therefore the development of project-level PMS followed. While network PMS use is incredibly important and results in great savings for state DOTs, cities, and counties, the actual pavement expenditures are done at the project-level and there is still a need to apply project-level PMS.
So what’s the answer? No matter how well designed, pavement must still be “managed” over its life. You must design and build the pavement with your best technology, then monitor performance and then maintain the pavement as needed.
What then should you do? The answer is straightforward.
- Design the pavement to the best of your ability.
- Then use your PMS database and monitor the performance and distress of that pavement.
- Update your database regularly with actual observed data.
- Properly analyze that data and you will be able to predict the preservation, maintenance, and rehabilitation needed to adjust the performance curve back to the designed level.
Keeping records and adjusting actual field performance trumps an incredibly complex design method only used prior to construction. PMS offers a more realistic and more practical solution to your pavement problems over time.
- Hudson, W.R., F.N. Finn, et all, “System Approach to Pavement Design Systems Formulation, Performance Definition and Material Characterization,” Final Report, NCHRP Project 1-10, California, March 1968.
- Haas, Ralph and W.R. Hudson, Pavement Management Systems, Krieger Publishing, Malabar, Florida 1978.