Using Work History Information to Improve Models
The availability of current work history and performance data allows agencies to develop and improve models used in a management system to predict future conditions and determine treatment effectiveness. This section describes and illustrates the use of this data to improve existing models.
Developing and Improving Asset Deterioration Models
An important function of an asset management system is the ability to predict asset deterioration rates so changes in condition over time can be modeled for use in planning and programming activities. In the absence of data, models can be developed based on expert judgment, but as historical performance trends are established based on actual data, the expert models should be replaced by or calibrated against the real data.
The AASHTO Transportation Asset Management Guide: A Focus on Implementation (2011) introduced the following thought process to help an agency evaluate their deterioration models and determine whether improved data is needed to enhance future forecasts:
- If there is disagreement with the timing for recommending a treatment, what is the difference? Does a difference of one to two years make a substantial difference to the program? This type of difference is typically the result of the program optimization models.
- If there is disagreement with the treatment, are the differences substantial, such as deck repairs versus bridge replacement? These differences are often the result of treatment rules but may indicate that deterioration rates are not correct. The deterioration model parameters may need to change (e.g., change traffic considerations or geographic location) or there may have been some work performed that the model is not aware of.
- If the differences are irreconcilable, the agency may decide to investigate the model setup and analysis further or may conduct research to see how other agencies have resolved similar issues.
Determining Treatment Effectiveness
The availability of work history and performance data also makes it possible to determine the effectiveness of different types of treatments over time. By adding cost information to an effectiveness analysis, an agency can determine the long-term cost-effectiveness of different treatment strategies.
North Carolina DOT
The North Carolina DOT conducted an analysis to determine the effectiveness of an open-graded friction course and a surface constructed with a FC-2 (friction course) gradation. Data from the pavement management database was used, including inventory data, construction information and pavement condition ratings. The performance data were plotted against the survey year for each pavement section where one of the two types of surface friction courses was applied. The results showed the performance of the open-graded friction course dropped at year 10, while the FC-2 graded surface dropped in performance at year 8. The study also found that all FC-2 sections had received another treatment by year 11. The results from the analysis were used to increase the use of open-graded friction courses across the state.
South Dakota DOT
In 2011, the South Dakota DOT initiated a project to revise the pavement deterioration models developed in 1997 using 17 years of historical pavement condition data. The tool for developing the models included features allowing all the condition-versus-age data points for each pavement meeting the family description (based on surface type and pavement structure) to be plotted on a graph, facilitating a comparison of the historical model and the recommended model based on the updated pavement condition information. In this example, the blue line (labeled as the user-defined model) represents the model being used in the pavement management system for predicting faulting on a thick, short-jointed doweled concrete pavement and the gold line (labeled as the regression equation). The regression analysis on the historical data, represented by the red data points, indicates faulting is occurring at a much more accelerated rate than was previously predicted. As a result, recommendations for addressing faulting were likely lagging the actual need observed in the field.
Illustration Showing How Historical Data can be Used to Modify a Deterioration Model
Source: South Dakota DOT. 2012. Technical Memo/Software Documentation
New Zealand Transport Agency
The Auckland Harbour Bridge corrosion protective coating system has been undergoing regular maintenance since the bridge opening in 1959. Historic practice was to spot abrasive blast corroded surfaces followed by spot painting and applying a full overcoat. While this process was effective in maintaining the protective coating, it also resulted in a significant amount of contaminates being discharged into the Waitematā Harbour despite the precautions being taken.
In an effort to reduce the discharge, various options have been considered taking into account the protective coating performance and longevity, with the aim to achieve the lowest practicable environmental discharge and whole of life costs.
One option involved collecting the abrasive blasting removal of the coating via the use of full scale containment to capture contaminants. However, it was found that this option would require strengthening of the bridge to safely carry the containment under wind loading at a cost of NZ$65M over a 10-year period.
As such, by undertaking a comprehensive review of the coating maintenance, a 40 years Coatings Maintenance Plan was developed. The identified lowest whole of life solution involved:
- On the land spans, use of full containment (where it could be supported from the ground), allowing for the full removal of the coating system via abrasive blasting, and its full reinstatement. These spans are to be left as long as possible before reinstating the protective coating, while ensuring minimal, if any section loss, to the steel superstructure.
- Spot repair and overcoating of other spans to maintain the existing coating for as long as practicably possible. A more proactive intervention approach is also adopted while using abseil techniques to minimize access costs.
- An outcomes based approach for consenting purposes that involved the establishment of low level discharge limits for contaminants deemed to be environmentally safe. This enables small areas of abrasive blasting without full containment for spans other than above land.
Thus, allowing for the continued corrosion protection of the bridge 125,000m2 external surface areas in a marine environment, while providing a cost effective and environmentally responsible solution.
Toronto Transit Commission
The Toronto Transit Commission initiated a review to determine optimal bus life for their fleet as well as assess the potential for hybrid propulsion technology. Through specialized modeling methods, a data-driven approach was used to assess the total cost of ownership (TCO) for their fleet vehicles. This review analyzed historical asset work order records along with other capital and operating expenses to help identify the optimal asset life cycle. The four key areas analyzed were:
- Procurement/Installation: Asset Design Specifications & Procurement Cost
- Operations & Maintenance: Labor, Parts, Fuel (if applicable), Consumable Items and Outsourced Work
- Overhaul/Rehabilitation: Major Asset Refurbishment/Component Replacement Cost (ex. Transit Bus Transmission Rebuild or Facility Rehabilitation)
- Disposition: Salvage Value (End-of-Life)
The model provided insights on when the optimal time to dispose of a fleet vehicle to minimize overall fleet cost, the comparative TCO of different vehicle types, and the relative effect and up-time benefit gained for different operations and maintenance activities or rehab treatments, by engine or other component types used in the fleet. They advanced their understanding of treatment effectiveness and allowed them to make more informed decisions about fleet renewal.
Washington State DOT
The Washington State DOT conducted a pavement life cycle analysis using performance and cost data that demonstrated the cost-effectiveness of its pavement preservation projects. Based on the results that are documented in their 2019 Transportation Asset Management Plan (https://www.wsdot.wa.gov/sites/default/files/filefield_paths/WSDOT_TAMP_2019_Web.pdf), the DOT instituted a “one touch policy” requiring all capital projects to have had at least one pavement maintenance treatment by Maintenance or contracted work forces before it can be programmed for a pavement preservation project. This has enabled the DOT to defer capital improvements on pavements by two to three years, or in instances of multiple touches, by four to six years at a very low cost. In 2018, the agency received an additional $6 million to test a similar program on bridges. In addition to being a cost-effective use of available funds, the programs have helped build buy-in among maintenance personnel by demonstrating the importance of the data they collect.