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Asset Sustainability Index: A Proposed Measure for Long-Term Performance

Chapter 4: Example of a U.S. Pavement Sustainability Ratio

Based on the concepts described in Chapters 1-3, Chapter 4 begins examining how an Asset Sustainability Index could be built using existing U.S. transportation agency data. The index as proposed in this report is a composite of pavement, bridge and maintenance condition data. This chapter begins the analysis by examining the pavement component of the index, which would be a Pavement Sustainability Ratio. When that ratio is combined with the Bridge Sustainability Ratio and the Maintenance Sustainability Ratio, they would form the Asset Sustainability Index as proposed. This example uses pavement condition and expenditure data from the Ohio, Utah and Minnesota Departments of Transportation.

Ohio Pavement Forecasts

The Ohio Department of Transportation (ODOT) produces annual and multi-year reports that illustrate past, current and projected future pavement conditions. The long timeframe of the Ohio DOT reporting is intended to complement its long-standing policy of placing infrastructure preservation as the central focus of its long-term budgeting. Catch phrases for this emphasis have changed over the years with such terms as sustaining a "steady state" of acceptable infrastructure conditions to a "fix it first" approach. The policy approach has been supported by a reporting process that keeps the agency focused on ensuring that its capital budgeting process, its project-selection decisions and its maintenance practices work in concert to achieve stable, long-term infrastructure conditions within the constraints of available revenue.

Figure 17: Conditions on Ohio's "priority system".

Figure 17 illustrates the pavement condition rating compared to the targeted condition for Ohio's priority route pavements. The chart illustrates trends from 2002 through 2020. Vertical bars indicate that Ohio's pavement condition rating ranged from 2002 through approximately 2018 at 95 percent or higher.  The target is displayed as a horizontal line which is at 90 percent for 2002 through 2011 when the target increased to 95 percent.  The chart illustrates that from 2002 through 2018 the conditions were above target and they are forecast to fall below the 95 percent target for the years 2019 and 2020.

Inherent in the ODOT infrastructure-management process is a long planning horizon. As seen in Figure 17 above, the agency looks at a nearly 20-year timeframe. The past years provide a trend line of investment levels and resulting infrastructure conditions that yield a solid analytical baseline for future forecasts. By extrapolating from a long trend line, the agency builds confidence in its pavement deterioration curves and other inputs for its forecasts of future performance. By looking at least a decade into the future for many of its major system elements such as bridges and Priority System pavements, it keeps the agency focused upon substantive planning to ensure steady, long-term conditions. As seen in Figures 17 and 18, the agency has raised the target for Priority System pavement conditions from 90 percent acceptable to 95 percent.

Figure 18: Ohio pavement conditions over 30 years.

Figure 18 is another bar chart that has verticle bars indicating the percentage of Ohio's priority routes that had deficient pavements. The chart covers the period from 1990 to 2014. It illustrates that in the 1990s, the percentage of pavements that were deficient increased substantially from 8 percent in 1990 to nearly 19 percent in 1997.  The department then steadily reduced pavement deficiencies until they reached the low levels illustrated in Figure 17. By 2001, the percentage of deficient pavements was as low as 3 percent. The chart also has a horizontal trend line that illustrates the pavement condition target. The target was to have no more than 10 percent of the pavements deficient from 1990 through 2011 falling to 5 percent beginning in 2012.

As seen in Figures 17 and 18, the agency has steadily surpassed its system condition goals for its Priority System. The Priority System in Ohio is similar to the National Highway System and it includes the Interstate Highway System and most multi-lane, divided routes. It consists of approximately 26 percent of the State's lane miles but handles 59 percent of the total vehicle miles of travel and 77 percent of the truck travel.[6] The State uses a Pavement Condition Rating (PCR) in addition to the International Roughness Index (IRI). The PCR is derived from an extensive visual survey of every route annually. The PCR is collected by a central crew of raters to ensure consistency. They measure more than 20 distresses including several that are indicative of structural pavement distresses such as reflective cracking, alligator cracking, pumping on concrete or composite pavements or broken slabs in concrete or composite pavements. The State also has compiled a construction history for every major pavement section, and it has a year-by-year history of past treatments and rates of PCR change by segment. This extensive history allows the department to forecast future conditions based upon scheduled treatments and each pavement's deterioration curve. The department has been stressing Asset Management for the past decade and that has contributed to substantial pavement condition improvements. In the mid-1990s, nearly 20 percent of the Priority System lane miles were below the acceptable PCR threshold of 65 and had substantial rates of annual degradation. As seen in Figure 18 above, the high deficiency volumes of the 1990s were addressed and system conditions have consistently surpassed the State's targets. The forecasted increase in deficiencies in the years after 2018 are largely, but not wholly, attributable to the State's forecasting methods. It forecasts conditions based upon the treatments programmed in the Statewide Transportation Improvement Program (STIP) as reported in the department's project-management system called Ellis. Because projects are not programmed yet for the later years, the Ellis program applies a deterioration curve to each pavement but does not yet capture the expected pavement treatments.

Table 12: Ohio pavement expenditures and outcomes.

Ohio Pavement Expenditures and Condition Results (Actual and Forecast)
  2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Total
General System Two-Lane Pavements $93 $93 $108 $113 $179 $186 $147 $149 $151 $152 $154  
Percent Acceptable     98% 97%   97%     97%  
Priority System Routine Maintenance $179 $179 $217 $228 $192 $199 $143 $145 $146 $148 $149  
Percent Acceptable       0.96   0.97   0.97     0.97  
Priority System Rehab and Replacement $150 $192 $150 $150 $150 $150 $172 $173 $175 $176 $178  
Paving State Routes in Cities $35 $35 $35 $35 $35 $35 $35 $35 $35 $35 $35  
Percent Acceptable       96%   95%   90%     90%  
Total Pavement Program Budgeted $457 $499 $510 $526 $556 $570 $497 $502 $507 $511 $516 $4,185
Projected Shortfall for Pavement Program             -$139 -$152 -$166 -$182 -$198 -$837
Source: Amended ODOT 2006-2007 Business Plan

ODOT reports expenditure levels in a fashion similar to that required by GASB, by some of the international financial reporting processes and similar to what is envisioned for the Asset Sustainability Index. Although the details of the financial expenditure processes have changed over the years, the basic concept has been used for more than a decade. As seen above in Table 12 from the Department's amended 2006-2007 Business Plan, pavement expenditures were to rise from $457 million in 2005 to $516 million in 2015. The department manages its pavements in three systems, Priority, General and Urban. The Priority System already has been described, while the General System is basically the two-lane system outside of city limits, which in the "Home Rule" State of Ohio is the DOT's responsibility. The Urban System is basically State and U.S. routes within cities, which in Ohio are a shared responsibility between the State and local governments. As seen in the Table 12, the percentage of acceptable forecasted pavement conditions for the three systems range from a high of 98 percent for the Priority System in 2008 to a low of 90 percent for the Urban System by 2015. The targets for PCR conditions on the General and Urban Systems in 2006 were a PCR of 55.

Table 12 also shows a forecasted financial shortfall in needed pavement investment starting in 2011 and continuing through 2015. In the 2006 scenario, ODOT was forecasting that within five years it would experience a shortfall starting at $139 million annually and rising to $198 million annually by 2015 if the conditions at that time continued. At that time, the major contributory conditions included a substantial increase in material costs which its Business Plan in 2006 indicated had risen at an overall rate of up to 12 percent a year. If those prices continued to escalate, and if the Federal highway apportionments remained virtually unchanged through 2015 as was forecast at that time, the Department was warning the public and policy makers of an $838 million gap between what was available and what was needed financially to meet its pavement targets.

Figure 19: Ohio pavement sustainability ratio and gap.

Figure 19 illustrates the asset sustainability index and the sustainability gap for pavements in Ohio from 2005 through 2015. It has vertical bars that indicate from 2005 through 2010 that the pavement sustainability ratio was optimum at 1.0. The pavement sustainability ratio fell to point 78 in 2011 and gradually declined to point 72 in 2015.  Correspondently in a trendline and a data table the chart illustrates that the sustainability gap increased from zero  in 2005 through 2009 rising in 2011 to 139 million dollars and increasing to 198 million dollars by 2015.

The financial information and the pavement condition forecasts provided in 2006 allow the illustration of a Pavement Sustainability Ratio for Ohio for this period of 2005-2015 as seen in Figure 19. It is a calculation of the amount budgeted, divided by the amount needed which results in the following as shown in Figure 19. It illustrates that from 2005 to 2010, the level of investment is adequate to sustain pavement conditions at ODOT’s targets. With expenditures relatively flat and materials costs forecast to rise, the Pavement Sustainability Index falls from 1.0 - adequate - to .78, or 22 percent below the amount necessary to provide stable, sustainable pavement conditions. Commensurately, a "Sustainability Gap" is illustrated on the secondary vertical axis and represents a cumulative gap of $838 million over the forecast period.

The Ohio DOT produces a long-term pavement condition forecast that is updated monthly and updated its Business Plan for the 2008-2009 and 2010-2011 biennium to address the earlier forecasts of impending pavement shortfalls. Table 13 depicts the total pavement expenditures for 2010 forecasted through 2017 as updated in the 2010-2011 Business Plan. They illustrate that ODOT increased pavement expenditures substantially, by an average of $109 million annually from 2010-2017, with a commensurate closing of the Sustainability Gap and the achievement of its pavement targets.

Table 13: Ohio pavement expenditures and outcomes.
Ohio Pavement Expenditure (Actual and Forecast) 2010-2012 Business Plan
Pavement Preservation Program   2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Pavement Preservation Budget $581 $578 $484 $612 $676 $674 $709 $742 $776 $812
Priority System Acceptable 98% 98% 98% 98% 97% 98% 98% 97% 97% 96%
General System Acceptable 95% 96% 96% 96% 96% 95% 95% 94% 92% 88%
Urban System Acceptable 97% 98% 98% 98% 97% 97% 97% 96% 94% 91%
(expenditures in $millions)                    

Table 14 illustrates the amended spending plan for 2010 through 2017 which was adopted in 2010 to address the under investment in pavements. As seen in Table 14, spending rose by between $139 million in 2011 to as much as $296 million in 2017 to fill the "sustainability gap" and to achieve the target of a Pavement Sustainability Ratio of 1.0. The calculation of the PSR and the computation of the delta to close the gap illustrate clearly the degree of additional investment necessary to sustain the pavement assets at the targeted condition through 2017. In 2006, ODOT forecasted the gap that was likely to occur if inflation continued as predicted. In 2010, when the effects of inflation had not diminished, ODOT increased pavement spending. If ODOT had been unable to re-direct the resources into the pavement program, the PSR would have reported to policy makers the future consequences of the under-investment and the relative size of the underinvestment.

Table 14: Increased investment and achievement of asset goals.
  2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
PSR Based on 2006 Pavement Budget 1.00 1.00 1.00 1.00 1.00 1.00 0.78 0.77 0.75 0.74 0.72    
PSR Based on 2010 Budget 1 1 1 0.91 0.96 1.18 1.04 0.97 1.00 0.98 0.96 1 1
Expenditure Delta $0 $0 $0 $0 $0 $0 $139 $152 $167 $182 $198 $260 $296
(in $millions)

ODOT balanced several ever-changing variables to develop the updated 2008-2017 budget estimate and pavement forecast. It noted that inflation continued to be a concern but that it had subsided substantially, which reduced the impacts of material costs that were experienced in the earlier Business Plan. However, rising costs on top of the already significant price increases of the past years remain a substantial influence on the pavement program. ODOT further reduced its Major New Construction Program, or the capacity-adding projects, in order to address the pavement gap.

Figure 20. Construction inflation influenced investment needs.

Figure 20 is a line chart illustrating the construction inflation rate experienced by the Ohio Department of Transportation from 2003 through 2011 and projected to 2017.  It illustrates that between 2003 and 2009, inflation rose by 60 percent. Construction inflation declined somewhat in 2010 and is projected to steadily climb again through 2017.  By 2017, the rate is projected to have increased by 200 percent compared to the base year of 2003.

A positive mitigating factor has been the increased service life Ohio has gotten from its pavements. Rates of annual degradation of untreated pavements have improved from a statewide average of 3.3 PCR points annually in the 1990s to as low as 2.5 percent PCR declines in the early 2000s. The difference equates to a 24 percent improvement in the longevity of the average pavement. In an annual pavement report, ODOT attributes improved pavement performance to a number of strategies, including tightened specifications, expanded preventive maintenance and enhanced decision making on treatment selection.

The granularity of the Ohio analysis allows for drilling into the underlying conditions that influence overall statewide pavement performance. This ability to "drill down" would allow the creation of a Pavement Sustainability Ratio for each district, each county or for any other subdivision, such as the highways within a Metropolitan Planning Organization (MPO) boundary. This granularity would allow an ODOT District or the neighboring MPOs to report on the PSR and total Asset Sustainability Index of its region. With the magnitude of a PSR known, the State, district or MPO could adopt long-range programming and pavement preservation strategies to sustain the pavement inventory.

Utah Pavement Sustainability Ratio Computation

In another example, the report generates a Pavement Sustainability Ratio using data from the Utah Department of Transportation (UDOT).

UDOT is considered to be one of the agencies with leading asset management processes and practices. As such, it provides the type of sophisticated long-term asset management forecast necessary to generate a credible Pavement Sustainability Ratio. The agency has a mature asset management approach that includes systematic and cost-effective maintenance, preservation, rehabilitation and operation of its physical assets. The UDOT Transportation Asset Management (TAM) approach tries to efficiently balance budget constraints, national issues, environmental priorities and public expectations in aligning its practices and applying asset management principles. With approximately 6,775 center lane miles (CLM) of roadway network to manage, the agency has successfully combined engineering, economics and sound financial planning with sound business practices in its decision-making.

To efficiently prioritize and manage its network the DOT has categorized the road network into four tiers based on the Annual Average Daily Traffic (AADT).

The four tiers/categories are:

These four tiers are sometimes combined for analysis purposes into three related categories, the Interstate, NHS and Non-NHS.

UDOT uses several factors (Condition Indices) to track the overall condition and performance of the roads. The Overall Condition Index (OCI) is the average of four primary Condition Indices. For asphalt, these are Ride, Rut, Environmental Cracking and Wheel Path Cracking. For concrete, these are Ride, Joint Faulting, Joint Spalling and Slab Cracking.

The agency has a strategy of "Good Roads Cost Less" (GRCL). Some of the interstate and level 1 road sections/segments have deteriorated to a state where they need minor and major rehabilitation. These roads will be managed on a "worst first" basis and are kept in serviceable condition through "Band-Aid" treatments until they can be reconstructed. However, the agency focuses on preservation of the roads that are in good condition to ensure that they continue to be in good condition. The preservation focus is to take care of the system to ensure sustaining its condition as "good" for the long-term.

UDOT has a strategic approach to financial planning as well as to engineering and implementation to address the long-term performance and sustainability of transportation assets. The strategy includes designing perpetual pavements on new capacity and pavement reconstruction projects. The agency defines perpetual pavement as "a pavement designed for a 50 year structural life, which will require a program of surface seals at set intervals throughout that 50 year life of the pavement. A perpetual pavement should not require any major rehabilitation or reconstruction work for the life of the pavement."

UDOT’s preservation treatment includes corrective maintenance, routine maintenance, preventive maintenance and minor rehabilitation. Corrective maintenance addresses immediate concerns of safety or pavement integrity and restores the pavement from unforeseen conditions to serviceable levels. Routine maintenance involves pro-active day-to-day activity to maintain and preserve pavement conditions at satisfactory levels. Preventive maintenance involves improving functional pavement conditions and extending the service life of the pavement. These are normally done on the surfaces of structurally sound pavements in good to fair condition and are lower-cost time-based treatments. The DOT's rehabilitation improves the pavement structure and addresses structural enhancements that extend service life or improve load-carrying capacity. Minor rehabilitation mainly addresses functional restoration of pavement surfaces due to age-related environmental cracking. Major rehabilitation usually increases pavement thickness to increase strength, addresses structural enhancements and accommodates increased traffic loading. Reconstruction replaces the entire existing pavement structure with similar or increased pavement thickness, thereby addressing pavements that have failed, become obsolete or have sub-grade issues.

In general, UDOT has put in place practices that help long-term sustainability of its transportation assets. These practices involve doing a Structural Overlay and Surface Seal in the 15th and 30th year. In between these two, alternate treatments of Surface Seal and Surface Rejuvenation are done every 3 years to sustain the condition of the pavement for 50 years.

Trade-Offs and System Conditions

The historic trend of UDOT’s pavement conditions are as shown in Figure 21. Figure 21 shows that the Overall Condition Index of the network is falling from 89.3 in 2004 to 76.5 in 2010. The number of center lane miles in "poor" condition is increasing from 3.73 in 2004 to 146.97 in 2010.

Figure 21: Utah pavement conditions over time.

Figure 21 illustrates pavement conditions on the Utah highway network.  It has a series of four categories of measures for each year from 2004 through 2010. The four series are total lane miles, lane miles in fair conditon, lane miles in good condition and lane miles in poor condition. The Total Lane Miles changes little over the period consistently being at about 6000 lane miles.  The Percent of lane miles in good condition gradually decreases from about 5800 miles in 2004 steadily falling to fewer than 3000 miles in 2010.  Concurrently, the number of the lane miles in fair condition increases from approximately 500 to more than 3800 by 2010. The miles of poor pavement remains very low throughout the period and are so small they are barely visible as a vertical bar. The chart also has a trendline depicting the Overall Condition Index.  It falls from slightly more than 90 in 2004 to about 75 in 2010.

Agencies are currently challenged with making the right decisions on where to invest and how much to invest in their transportation assets. With limited funds, priorities will have to established and trade-offs will have to be made, both across asset categories as well as within asset categories. Under such circumstances, some assets will suffer from under-investment. The goal is to ensure long-term sustainable management and maintenance of the transportation assets and therefore, to ensure that any under-investment occurs in areas of least impact. Under investment, if applied selectively, may result in poorer condition and performance of some of the assets or if applied across the board, can result in poorer conditions even for high-priority assets. The computation of a Pavement Sustainability Ratio quantifies and brings to the forefront the projected results based on anticipated investment levels. It facilitates and triggers objective trade-off decisions and helps in better financial planning with the goal of making optimal use of available funds.

Figure 22: Utah pavement budget versus condition.

Figure 22 is a bar chart with additional trend lines that illustrate projected budgets compared to the  projected overall pavement condition index.  The overall message of the chart is that if pavement expenditures remain steady at about 170 million dollars from 2013 through 2030, the overall pavement conditions will decline with the greatest decline being on the non-National Highway System routes. The chart begins in 2012 with a projected budget of just over 100 million dollars for minor pavement preservation.  The budget increases in 2013 to about 170 million dollars and remains at that level through 2030.  The trendlines illustrate the projected effect upon four conditions.  The trendline for the average Interstate Highway System Overall Condition Index shows that the index begins in 2012 at about 89  and stays about 90 through 2025 when it gradually declines to about 85 in 2030.  Another line depicts the average Overall Condition Index for the National Highway System. The NHS OCI starts at about 82 and remains at that level through 2025 when it declines in 2030 to about 78.   The trendline for the Overall Condition Index for the entire highway network stays steady at about 75 from 2012 through 2015 when it begins to decline. By 2030, the overall highway network OCI is about 60.  For routes not on the National Highway System the decline in conditions is more significant.  The non-NHS routes have an OCI of about 70 in 2012 and that falls rapidly after 2015. By 2030 the non-NHS routes have an OCI of about 45.

The discussion below focuses on the condition of the roadway network as well as budgets available and required to manage and maintain optimal pavement conditions. The information is used to compute a Utah PSR.

Figure 22 shows the Overall System Condition (OCI) of the different tiers of the roadway network based on projected funding for years from 2012 to 2030.

The figure shows the Overall System Condition (OCI) index falling from 74.72 in 2012 to 61.4 in 2030. Figure 22 also shows the OCI for the different tiers of roads in Utah. In the trade-off required by the budget constraints, the different priorities assigned to the three tiers (Interstate, NHS and Non-NHS) of the system are reflected in the difference in the condition of these tiers for the analysis period.

The condition for the Interstate system drops from an OCI of 87.0 in 2012 to an OCI of 83.6 in 2030, the condition for the NHS drops from an OCI of 80.04 in 2012 to an OCI of 74.94 in 2030 and the condition index for the non-NHS drops from an OCI of 71.13 in 2012 to an OCI of 46.16 in 2030.

Figure 22 also shows how the agency is using the available budgets and making trade-offs in managing and maintaining the performance and condition of the roadway network. The approach used gives higher priority to the more heavily used roads and to those carrying heavier loads as compared to those that have lesser traffic and carry lighter loads.

The highest priority is being given to the Interstate system. Second priority is given to the NHS system that is more used than the non-NHS. The third priority is given to non-NHS, the lesser used of the three systems.

Tradeoffs and Backlogs

Another way to depict the long-term consequences or outcomes of investment decisions is to measure backlogs of needed treatment.

Backlog is the term being used in this document for the roadway sections that require treatment but do not receive maintenance or rehabilitation activity.

Figure 23 shows the backlog of Interstate, NHS and non-NHS systems for the period starting in 2012 through 2030. When there are fewer constraints with availability of funds by moving funds across the different fund categories, agencies can be more liberal in performing preservation and maintenance activities on all tiers of pavements. As funds become more limited, ensuring sustainable performance-based management of assets requires prioritizing and making trade-offs between how much to spend and when to spend monies on the Interstate, NHS and non-NHS system.

Figure 23: Backlog of pavement treatments.

Figure 23 illustrates the backlog of needed pavement treatments on the Utah National Highway System and non-National Highway System between 2010 and 2030.  The stacked, vertical bars indicate that the backlog of treatments on the Interstate Highway System remain relatively low with a backlog of 523 miles in 2010 decreasing to 281 by 2020 and increasing to 519 miles in 2030.  On the National Highway System the backlog grows from 602 miles in 2010 increasing to 701 by 2030.  For the non-National Highway System, the backlog is much larger and grows more rapidly. The backlog in 2010 is 2530 miles growing to 3465 miles by 2030.

Figure 23 shows that the backlog on the Interstate system is being kept to a minimum, the backlog on the NHS is higher and the backlog of miles not addressed by maintenance and rehabilitation activity in the non-NHS system increases from 2,530 CLM in 2012 to 3,456 CLM in 2030. Figure 23 also shows that the total backlog increases from 3,655 CLM in 2012 to 4,685 CLM in 2030.

Figure 24 shows the condition of the interstate system after trade-offs have been applied to optimize the use of available funds. It shows that the Interstate in "good" condition increases from 1,481 CLM in year 2011 to 1,503 CLM in 2012. The overall CLM for interstate in "good" condition varies minimally between 1,490 CLM and 1,450 from 2013 through 2015. The CLM in "good" condition increases from 2020 through 2025. In 2030 the CLM in "good" condition decreases while the CLM in "poor" condition increases.

Figure 24: Utah Interstate pavement condition trends.

Figure 24 illustrates the projected pavement conditions for the Utah Interstate Highway System from 2011 through 2030.  The stacked, vertical bars indicate that the miles of pavement in good condition begins in 2011 at 1418 miles and remains approximately at that level through 2025 when the miles of good pavement increases to 1582 before decreasing in 2030 to 1354. The overall trend is that the conditions remain overall about the same for the miles of pavement in good condition on the Interstate Highway System.  The miles of Fair pavement also remains about the same through the period. The miles of fair pavmement is at 393 miles in 2011 and undulates somewhat until 2030 when they are at 420 miles. However, the miles of Interstate Highway System pavement in poor condition increases from zero in 2011 through 2015 to 27 point six miles in 2020 and increases to 100 miles by 2030.

Figure 24 also shows the corresponding change in the average OCI for the interstate system from year 2011 to 2030. It shows the OCI for the interstate system improving from 86.48 in year 2011 to 88.63 in year 2020.Figure 24 also shows that the projected OCI drops to 83.57 in 2030.

Figure 25 shows the number of CLM for the NHS from 2011 to 2030 in "good", "fair" and "poor" condition. It also shows the statewide average OCI improving from 79.47 in year 2011 to 80.04 in year 2012 and remaining around 80 from year 2012 through year 2020 and then dropping progressively to 74.94 by 2030.

Figure 25: NHS conditions and trends.

Figure 25 illustrates projected pavement conditions on the National Highway System in Utah from 2011 through 2030.  It illustrates that the miles of pavement in good condition is at 545 miles in 2011 and improves somewhat through 2014 when they peak at 567 miles and then decline overall to 422 miles by 2030.  For the pavements in fair condition, they begin at 451 miles in 2011 and remain relatively steady until 2020 when they decline to 377 miles and then increase to 492 miles by 2030.  The miles of National Highway System pavements in poor condition are at 18 miles in 2011 and decrease gradually down to 3 miles by 2015 but then steadily increase until they reach 100 miles on 2030.

Figure 26 shows the condition of the non-NHS in "good", "fair" and "poor" from 2011 through 2030. It shows the CLM in "fair" condition decreasing from 2635 in year 2011 to 1103 in year 2030. It shows a corresponding increase in the "poor" condition for the same period with CLM of "poor" condition increasing from 155.2 to 2526.9. The figure also shows the number of CLM in "good" condition decreasing from 1059 in year 2011 to 219 in year 2030. This overall fall in system condition is reflected in the OCI decreasing from 72.3 in 2011 to an OCI of 46.165.

Figure 26: Non-NHS condition and trends.

Figure 26 illustrates the pavement conditions projected for the non-National Highway System from 2011 through 2030. It illustrates that the number of miles in good condition declines from 1060 in 2011 to 219 by 2030.  The miles in fair condition also decrease from 2635 miles in 2011 to 1104 miles by 2030.  The number of miles in poor condition increase from 155 miles in 2011 to 1063 in 2020 and then even more rapidly increases to 2526 miles by 2030.

Computing Long-Term Optimum System Conditions

Figure 27 shows the optimal long-term conditions that can be achieved for the Interstate System (IS), NHS and non-NHS systems and the budget required to sustain the optimal OCI for the system from 2011 through 2030, assuming that there are no budget constraints.

Figure 27: Budget need for optimal conditions.

Figure 27 illustrates the budget required to achieve the optimum Overall Condition Index pavement conditions for four highway networks in Utah. The budget would be 210 million dollars annually for years 2011 through 2015 and then increase to 230 million for the years 2020 through 2030.  With that level of investment, the OCI on the Interstate Highway System would be between 89 point 5 and 91 through 2015 and would decline slightly to 88.5 by 2030.  The OCI for the Level 1 NHS would be at between 83 point 5 and 86 from 2011 through 2030.  The OCI for the non-NHS would be between 80 and 82.5 from 2011 through 2030. The OCI for the Level 2 systems would be between 76 and 78 from 2011 through 2030.

Figure 27 shows how with appropriate long-term financial planning an agency can compute the optimal amount of funds required to sustain the long-term performance and condition of the roadway network.

To identify the optimal conditions that can be achieved for a long-term period of nearly 20 years in the future, different scenarios of conditions that can be achieved for different budget amounts for each tier of the roadway are generated. These multiple scenarios are then analyzed to identify the minimum budget amount required to achieve and sustain optimal pavement conditions in the future.

Figure 27 shows the optimal condition that can be achieved for each of the tiers of the roadway. The total annual amount required to sustain the optimal OCI is approximately $210 million in years 2110 through 2015. The budget required to sustain the optimal OCI beyond year 2015 increases to $230 million dollars annually.

Utah DOT -The Pavement Sustainability Ratio

Figure 28: Utah pavement sustainability ratio.

Figure 28 illustrates the pavement sustainability ratio overall for the Utah DOT based on the analysis described.  The optimum sustainability ratio is 1.0 but based upon available budgets the actual sustainability ratio will vary from a low of approximately point 5 in 2012 and then will increase to about point 8 in 2013 and remain at point 8 until 2020 when it will fall to about point 75.  The optimal that should be budgeted to achieve all condition targets is 210 million dollars  in 2012 through 2015 and should increase to 230 million dollars for the period 2020 through 2030.  However, actual expenditures are forecast to be  at about 170 million dollars annually from 2013 through 2030.  The budget deficit varies from a high of approximately 90 million dollars in 2012 to about 40 million dollars in 2013, 2014 and 2015 and increases to about 60 million dollars from 2025 through 2030.

The available and required budgets (for optimum OCI) as discussed above are consolidated in Figure 28 along with the budget deficit to maintain optimum conditions. Figure 28 also depicts the Goal PSR (assuming optimum budget availability) as well as the projected PSR based on available budgets.

A Pavement Sustainability Ratio is a metric calculated by dividing the amount budgeted for pavement maintenance and preservation over time by the amount needed to achieve a specific pavement condition target.

This PSR= 1 is shown in purple in Figure 28. The PSR is computed as:

Pavement Budget
Pavement Needs
 =   Pavement Sustainability Ratio

Figure 28 shows the currently projected PSR based on available budgets in orange. The PSR is 0.4 in 2012, showing a 60 percent shortfall from optimum needs. It increases to 0.8 in 2013 and remains at 0.8 until 2015. After 2015, the PSR drops from 0.8 to 0.74 in 2020 and remains at 0.74 through year 2030.

As shown in the UDOT example, a Pavement Sustainability Ratio can be computed using the asset condition forecasts and related investment needs generated from a mature U.S. State asset management process. The example also illustrates that the PSR thus is a tool that can be effectively used to consolidate the analysis of the overall system conditions, required budgets to maintain optimum system conditions, and available budgets (representing fiscal constraints) into a single metric. The PSR can therefore also be used to effectively illustrate and communicate to all stakeholders the budget status and investment needs required to maintain optimum system conditions.

Minnesota Pavement Sustainability Example

This example illustrates how a Pavement Sustainability Ratio could be calculated using a third State's data. This analysis also illustrates how long-term system forecasts can be used to illustrate the consequences of tradeoffs.

Figures 29, 30 and 31 below from the Minnesota DOT (MnDOT) are typical of the type of information that often is portrayed by States and which could contribute directly to a Pavement Sustainability Ratio. Figure 29 illustrates that the agency has struggled since 2001 to reach its pavement-condition targets and that it has had to accept gradually lowering conditions, particularly on its Non-Principal Arterials. Figure 30 illustrates that the percentage of "Poor" Ride Quality Index miles also has steadily increased and are forecast to rise significantly in the next four years. Even more germane to the concept of an Asset Sustainability Index is Figure 31. It illustrates that the Remaining Service Life of the State's pavements has steadily declined, by as much as 43 percent between 2001 and 2010 for the Non-Principal Arterials. Figures 30 and 31 illustrate the type of long-term implications that GASB 34 and TAM guidelines seek to capture. Those figures show the erosion in the "robustness" of the pavement inventory. With its significantly reduced Remaining Service Life, the pavements have less "elasticity" to sustain a temporary budget reduction, to withstand increased traffic loadings or other impacts. In addition, future costs likely will rise as it is more expensive to rehabilitate a deteriorated pavement than to maintain a good one. As such, the "value" of the 2014 pavement inventory is significantly less than the value of the 2001 inventory that had a greater Remaining Service Life. In simple terms, it would be analogous to the value of a car with 50,000 miles compared to one with 71,500 miles, or 43 percent more miles.

Figure 29: MnDOT "good" ride quality.

 Figure 29 illustrates the actual and projected conditions of pavements in Minnesota from 2001 through 2014.  The target for principal arterials is to have 70 percent of pavements with a good ride quality index and to have 65 percent of the non-principal arterials with a good ride quality index. The actual conditions for the principal arterials was that 76 point seven percent were in good condition in 2001 and that decreased to 63 point 6 percent good condition by 2003. The percent in good condition varied between a low of 63 point four percent in 2004 to a high of 90 point two percent in 2010. The principal arterials are forecast to remain around 69 percent with a good rating from 2011 through 2014.  For the non-principal arterials, the percentage in good condition was 70 point three in 2001 declining to 64 point 8 in 2002 and falling to 55 point three percent in 2003.  From 2004 through 2010 the percentage in good conditon varied from a low of 55 point three to 61 point one.  Forecasted for 2011 through 2014, the non-principal arterial are to have 59 percent good in 2011 and that should increase slightly in 2012 before declining to 57 point percent in 2014.

Figure 30: MnDOT "poor" ride quality index.

Figure 30 illustrates the rising trend in the percentage of the Minnesota highway system that has poor pavement.  In 2001, the amount of poor ride quality pavements on principal arterials was 1 point 5 percent and it was 2 point 1 percent for non-principal arterials.  The amount of poor ride quality pavement steadily increased on both the principal arterials and the non-principal arterials rising to 3 point 7 percent on the principal arterials and to 6 point 8 percent on the non-principal arterials by 2010.  The percentage of poor pavements is expected to continue increasing according to the department's forecasts and to reach 4 point 8 percent of the principal arterials by 2014 and to reach 10 percent of the non-principal arterials by 2014.

Minnesota defines Remaining Service Life as the number or remaining years until a pavement declines to a 2.5 out of 5 in its Ride Quality Index. The rating of 2.5 indicates the pavement is in need of rehabilitation to provide an acceptable ride. The terminal condition of 2.5 does not indicate the road is unusable, only that its condition cannot be restored without significant rehabilitation.

Figure 31: MnDOT remaining service life.

Figure 31 illustrates the decrease in remaining service life for Minnesota pavements.  In 2001, the principal arterials had an average remaining service life of 14 point 8 years and that steadily declines until by 2010 the remaining service life average for principal arterials is only 10 point one years.  For non-principal arterials, the remaining service life was 13 point 4 years in 2001 and steadily declined to 7 point 7 years in 2010.

Minnesota's data and its analyses clearly inform policy makers of the pavement-deterioration trends and their causes. The first important trend is declining overall revenue forecasts.

Figure 32: MnDOT declining program projections.

Figure 32 illustrates the planned investments overall for the Minnesota DOT from 2011 to 2020. The vertical bars illustrate a steady decline in expenditure level with expenditures at 968 million in 2011 declining to 686 million in 2013, rising in 2014 to 722 million and then to 785 million in in 2015 and gradually declining to 596 million in 2020.

As Figure 32 illustrates, capital revenue forecasts decline substantially as fuel tax receipts stagnate, operating costs rise, less bond income can be afforded and Federal apportionments remain unclear.

Figure 33: MnDOT's declining pavement investment levels.

Figure 33 elaborates upon Figure 32 by focusing upon expenditures for pavements in Minnesota forecast from 2011 to 2020.  The expenditures are at their peak in 2011 at 355 million, and then decline rapidly to 221 million in 2021.  Forecasted expenditures vary with a low of 186 million dollars in 2014 and rising slightly to 211 million dollars by 2020.  The overall trend is for a decline in pavement expenditures by more than one third between 2011 and 2020.

Figure 33 illustrates that commensurate with the overall decline in spending, pavement expenditures will fall. This decrease in pavement spending comes at a time of enhanced investment in bridges, following the collapse of the I-35 Bridge in Minneapolis. A special legislative directive requires the department to replace 120 fracture critical or structurally deficient bridges. Approximately 32 percent of all STIP funding from 2011 to 2020 will be devoted to bridges, with two-thirds of that devoted to these structures.[7] The results are predicted to be that the percentage of bridges meeting their structural condition goals will rise from 87 percent in 2009 to 89 percent in 2014, with conditions through 2020 projected to remain above the target of 84 percent.

MnDOT predicts that it will meet several important long-term targets in the 2011-2020 planning period. Targets it expects to meet include:

However, the expected lower revenue and investment-tradeoff decisions will result in the department being unable to meet its pavement targets particularly on the Non-Principal Arterials. The number of State highway miles with good pavement conditions will decrease and the number of State highway miles with poor pavement condition will increase from 990 miles in 2009 to 2,528 by 2019.

The estimated cost of the needed investment to sustain the Minnesota pavement conditions was not directly available for this report. MnDOT's process for generating pavement needs was between annual planning cycles and the necessary analyses to estimate the financial need for pavements to sustain conditions was not available. However, the Minnesota data that were available illustrate that with some additional computer runs, that MnDOT could produce a pavement sustainability ratio as described in this report. The type of analysis possible with the MnDOT processes likely would illustrate that while bridge conditions were sustainable, the pavement conditions are not at current investment levels. Substantial pavement investment increases will be necessary, and a Pavement Sustainability Ratio would illustrate the magnitude and cost of the needed investment.

Updated: 03/26/2013
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