4. Developing pavement deterioration models with regular maintenance,
5. Developing pavement deterioration models with delayed maintenance,
6. Estimating maintenance budgets without delayed scenarios,
7. Estimating maintenance budgets with delayed scenarios, and
8. Reporting the impact of delayed maintenance and its consequences.

5.1.1 Establishing Asset Inventory

The airport needs to have a pavement inventory database where the dimensions and category (primary, secondary, and tertiary) of an airfield pavement can be stored. The pavement element information needed in the inventory is provided in Table 5-1 (FAA 2014b, FAA 2022b). The inventory should have the length and width of the runway. Pavement structure type, for example, concrete, asphalt, or rigid over asphalt overlay, and its surface material, are necessary. It is important to have details about pavement structure, e.g., thickness, subbase aggregate types, and the date of construction. It is also important to have the dates of minor and major rehabilitation, if applicable. The inventory should have information about surface and subsurface drainage provided during the pavement construction. The pavement design information related to the strength of the pavement and design loads of the pavement should be recorded in this database. The inventory should consist of any other information that helps airport asset managers maintain and rehabilitate the pavement, such as maintenance activities performed and frequency. These data will assist in identifying the corrective activities needed to bring the pavement to the level of service required. Most large-hub airports keep these pavement records in a pavement management system, most commonly FAA PAVEAIR. This information is key in determining the annual maintenance cost with or without delays.

5.1.2 Performing a Condition Assessment

All airports assess the conditions of their airfield pavement in accordance with FAA Advisory Circular 150/5380-7B Airport Pavement Management Program (PMP) which “is mandatory for

Table 5-1. Runway pavement element information (FAA 2014b).

all projects funded with federal grant monies through the Airport Improvement Program (AIP) and with revenue from the Passenger Facility Charges (PFC) Program.” Generally, condition assessment of pavement is done by determining the PCI of the pavement, in accordance with ASTM 5340—Standard Test Method for Airport Pavement Condition Index Surveys. PCI is “a numerical rating of the pavement condition that ranges from 0 to 100, with 0 being the worst possible condition and 100 being the best possible condition” (FAA 2022c). The PCI number shows the pavement’s present condition based on the distress observed on its surface. Distress type and quantity are used to determine values deducted from 100 to calculate the PCI. Asphalt and PCC-surfaced pavements each have their own set of distress types. While some types of pavement distress (i.e., corner breaks, shattered slabs, alligator cracking, rutting) indicate a structural failure, the majority of pavement distress is caused by age or environmental factors. Therefore, most pavement maintenance is aimed at extending the functional life of the pavement as opposed to addressing a structural failure. Figure 5-2 shows the condition of the pavement based on the PCI numbers. Pavement maintenance treatments are more cost-effective when applied while the pavement is still in good/satisfactory condition. As pavement falls into the fair category, actions like a mill and inlay often become the most effective means of pavement rehabilitation. Below a PCI of 55, a mill and inlay may require additional work (thicker inlay, base repairs, additional patching) to perform as intended, and reconstruction will start to become more competitive on a life-cycle cost basis. Below a PCI of 40, complete reconstruction is typically the only feasible rehabilitation option. The PCI values are used to establish a runway’s rate of deterioration and to identify future rehabilitation needs. PCI values are also used in prioritizing, funding, and executing maintenance and rehabilitation on the pavement section. Condition assessment is key in determining the health of the pavement and in predicting the rate of deterioration.

Pavement inspection is one of the most important parts of the PMP of any airport. Airports can use the pavement condition survey to determine PCI and use these values to develop pavement performance predictions. It is necessary that the PCI value is determined in accordance with the procedures contained in ASTM D5340, Standard Test Method for Airport Pavement Condition Index Surveys (FAA 2014b). Airports should also maintain runway pavements that provide surfaces with adequate friction characteristics under all weather conditions. AC 150/5320-12 provides the process and frequency of skid resistance testing. Airports should be careful about using visual observations for skid resistance determination, because the visual pavement inspections do not

adequately predict skid resistance. Roughness measurements can be helpful when there is evidence of roughness issues, usually in the form of frequent pilot complaints. Roughness measurements are of greater value when the pavement is in very good condition with little or no distress. They have less value if reconstruction is imminent. AC 150/5380-9, Guidelines and Procedures for Measuring Airfield Pavement Roughness, provides guidelines and procedures for measuring and evaluating runway roughness.

Various types of distress in asphalt and concrete pavement develop over time. Air traffic loading and climate/weather exposure are direct contributors to distress, leading to the need for repair and maintenance. Table 5-2 provides some of the distress seen in these two types of pavements (FAA 2014a).

5.1.3 Identifying and Updating Pavement Maintenance and Rehabilitation Activities and their Unit Costs

Identifying the major maintenance and rehabilitation activities that need to be performed on asphalt and concrete runways and taxiway pavements is important. FAA AC 150/5380-6C provides information on maintenance activities for various types of distress on asphalt and concrete pavement. Tables 5-3 and 5-4 provide the types of suggested maintenance for these two types of pavements to keep pavement in good condition, as well as to increase the pavement life. This AC also provides the types of materials used to repair asphalt distress and concrete pavements.

Once these repairs and maintenance activities are identified, the unit cost of performing them needs to be determined. These data can be updated from the contractor’s unit bid price if the maintenance work is outsourced. If in-house staff performs these activities, then the labor hours

Table 5-2. Types of distress on asphalt and concrete pavement.

need to be tracked during the maintenance. The cost of labor hours used to maintain the pavement can be calculated by the total hours spent multiplied by the cost of labor per hour. The materials and equipment costs can be included to determine the total maintenance cost. It is a good estimating practice to add some contingencies based on the risks associated with repair. The total cost per unit of these maintenance activities should be updated in the CMMS software so that the maintenance budget for future years can be calculated.

It is critical to determine the rehabilitation and reconstruction cost of pavement for budgeting. These costs can be determined using RSMeans cost data or the Engineering News-Record’s cost data dashboard. The maintenance, rehabilitation, and reconstruction costs per unit are necessary to determine the regular maintenance budget, as well as to quantify the consequences of delayed pavement maintenance.

The research team collected extensive cost data on pavement maintenance and rehabilitation from airport projects around the United States. These data have been used to determine typical costs for the maintenance and rehabilitation of asphalt and concrete runway pavements. The team determined maintenance and rehabilitation unit cost of asphalt and concrete pavement based on PCI. These unit cost data varied based on the airport size (small-, medium-, and large-hub airports). They can be found in the supporting spreadsheet tools supplemental to this report. Airports can use these tools to estimate the regular and delayed maintenance and rehabilitation cost of the asphalt and concrete pavements.

5.1.4 Developing Pavement Deterioration Models with Regular Maintenance

FAA researchers have collected PCI values of numerous airport pavements and have developed a deterioration model to predict the PCI values based on the age of the pavement. These regression models are developed based on the pavement types and are prepared separately for runways and taxiways. These models can also differ based on airport location and size. The team collected PCI values of numerous airport pavements of various ages and developed deterioration models for all sizes of airports for asphalt and concrete pavements. Equation 5-1 shows the regression models for predicting PCI values based on the asphalt pavement’s age, assuming the required maintenance work has been completed regularly in airports.

Figure 5-3 shows a deterioration trend based on the age of asphalt pavement of an airport. It shows that the deterioration of airfield pavement is steep in the beginning and evens out in the middle. The model shows that it generally takes 36 years to reach the PCI value of 40, assuming the implementation of regular maintenance and rehabilitation. It shows that, on average, there is a reduction of 1.7 PCI value per year.

Equation 5-2 shows the deterioration model of plain concrete runway pavement for airports. In this case, the deterioration of the runway pavement is linear.

Figure 5-4 shows the deterioration shape of a hypothetical airport’s plain concrete pavement, which is similar to the asphalt pavement. Unlike the asphalt pavement, the PCI value of concrete pavement will not reach 0 at the age of 45 years. The plain concrete pavement will reach a PCI value

of 23 at the age of 45 years. The model shows that it generally takes 40 years to reach a PCI value of 40, assuming the implementation of regular maintenance and rehabilitation. On average, the concrete pavement PCI value will be reduced by 1.5 per year, which is lower than that of asphalt pavement.

5.1.5 Developing Pavement Deterioration Models with Delayed Maintenance

When collecting PCI data from airports, the research team found that airports did not collect PCI data for runway pavements when maintenance was not performed. Therefore, it is impossible to develop the deterioration model based on delayed or no maintenance. However, to determine the deterioration trend of asphalt and concrete runway pavement for airports, the research team assumed that asphalt and concrete pavement will last for 20 and 30 years, respectively, if regular maintenance is not performed. Therefore, for asphalt runway pavement to go from a PCI value of 100 to 40, it will take 20 years. This is an average reduction of 3 PCI values each year. Similarly, for concrete runway pavement, the average reduction of PCI value per year will be about 2. Therefore, the research team reduced 3 PCI values from the PCI value of the asphalt runway pavement in a particular year. The same method was used to determine the PCI value of concrete runway pavement, with 2 PCI values reduced from its original value in a particular year. Reducing the PCI values for asphalt and concrete pavement by 3 and 2 seems reasonable because, in the regularly maintained scenarios, the average PCI value reduction for asphalt and concrete pavements are 1.7 and 1.5, respectively. Therefore, if the PCI value of the pavement of an airport in the year 2021 is 70, then delaying maintenance by one year will make the PCI values of asphalt pavement and concrete pavement 67 and 68, respectively. This reduction of PCI values is higher than the average reduction of PCI values in regularly maintained asphalt and concrete runway pavements. The following example demonstrates the process of predicting the PCI values of asphalt and concrete runway pavement with and without delayed maintenance.

For an airport with an asphalt runway pavement that is 5 years old, based on a regular maintained deterioration model, the PCI value of the pavement will be calculated using Equation 5-1.

The PCI value of the pavement this year will be 84.4. If the maintenance budget needs to be calculated for the pavement this year, a value of 84.4 will determine the maintenance budget of the pavement. However, if the maintenance of this pavement is delayed by 3 years, then the predicted PCI value based on no maintenance will be:

PCI = 84.4 – 3 * 3 = 75.4

However, if regular maintenance is done, then the pavement’s PCI value after 3 years will be 77.9 based on the regular deterioration model formula shown in Equation 5-1. This demonstrates that there is a decrease of 2.5 PCI after delaying maintenance by 3 years, thus significantly increasing the cost of pavement maintenance. Similar procedures can be used to determine the difference between the PCI values of regular and delayed maintenance concrete pavements.

5.1.6 Estimating Pavement Maintenance Budgets without Delayed Scenarios

Using the deterioration models for regularly maintained asphalt and concrete runway pavement, the PCI values of these pavements can be predicted based on their age. Once the predicted PCI values are calculated for these two types of pavements for the yearly budget, the total regular maintenance budget can be calculated by multiplying the area of the runway pavement and the maintenance cost per square foot corresponding to that PCI value. To calculate the maintenance

cost, it is necessary to have the average maintenance cost per square foot of the runway area for every PCI value starting from 100 to 40. After PCI values reach 40, the runway pavement needs to be reconstructed. Therefore, the maintenance cost per square foot on asphalt and concrete runways needs to be updated every year for an accurate estimate of the maintenance cost. In general, the maintenance of pavement is determined based on the types and level of distress found during inspection. However, maintenance activities and PCI values are correlated. The maintenance cost spent on asphalt and concrete runway pavements can be determined for each PCI value by developing a regression model. The maintenance costs per square foot for each value of PCI can be used to estimate the maintenance cost of the asphalt and concrete runway pavement. The spreadsheet tools developed to determine the regular and delayed maintenance costs of asphalt and concrete runway pavements use this maintenance cost derived from the regression model. The maintenance cost of asphalt or concrete runway pavements used in the tool is the 2020 base cost. Inflation rates have been collected from the Bureau of Labor Statistics to determine the inflated cost (BLS 2022a). The inflation cost index of concrete pavement since 1971 shows that the inflation rate of ready-mix concrete is 4.07% per annum. Similarly, the inflation rate for asphalt was found to be 2.93% per year (BLS 2022b).

5.1.7 Estimating Pavement Maintenance Budgets with Delayed Scenarios

The total maintenance budget of asphalt or concrete runway pavements in a delayed scenario can be calculated by using the linear deterioration trends discussed in Section 5.1.4. Once the PCI value of the asphalt or concrete runway pavement is determined for the year after considering the delayed scenarios, the total maintenance cost can be estimated by multiplying the maintenance cost per square foot with the area of the runway pavements. Due to decreased PCI values, the maintenance cost of the delayed scenario runway pavements will always be higher than that of regularly maintained runway pavement. As mentioned previously, this delayed maintenance cost considers only monetary maintenance costs without considering other costs such as safety, passenger comfort, etc.

5.1.8 Reporting the Impact of Delayed Pavement Maintenance and its Consequences

Airport asset managers need to know the extra cost incurred when the maintenance of asphalt or concrete runway pavement is delayed by a number of years. The difference in the maintenance costs can be presented to higher authorities to validate that it is beneficial to spend money on regular maintenance rather than wait. The spreadsheet tool developed by the research team (found in Section 2.1 of the Quick Guide) can compute both the regular and delayed maintenance costs by selecting delayed scenarios. The user can also select the default price inflation rate or enter a new inflation rate for asphalt or concrete pavement to calculate the delayed maintenance cost. As maintenance is delayed, the maintenance cost for asphalt or concrete runway pavement will be inflated, and the updated cost needs to be considered when estimating the total maintenance cost of runway pavements. The tool also has the option of selecting a discounted rate, so that the future value of maintenance costs can be converted to present value for comparison purposes if an airport decides to use the discounted rate for its investments. Generally, private sectors use the discounted rate to determine the value of money in relation to time.

The research team has created a hypothetical airport runway with its own dimensions and pavement age to show the consequences of delaying maintenance on asphalt and concrete pavements. Two- and 5-year delayed scenarios were selected. To report the impact of delayed maintenance and its cost consequences, the team considered hypothetical data. The team hypothesized that

Table 5-5. Case study data of a hypothetical small-hub airport.

pavements had PCI values of 90, 80, or 70, to demonstrate the effects of aging runway pavement on the delayed maintenance cost. Table 5-5 shows the hypothetical small-hub airport case study data.

Case Study Results of the Consequences of Delaying Maintenance on Airport Runway Pavements

Results of Delaying Maintenance on the Concrete Runway Pavement of an Airport

The team used the spreadsheet tool to determine the consequences of delayed maintenance on an airport with concrete runway pavements. Three different pavements with PCI values of 90, 80, and 70 were selected. Figure 5-5 shows the total maintenance cost of this airport for concrete pavement with and without a maintenance delay. The budget was prepared in 2022 and will be used for 2023, so the maintenance cost calculated for the base scenario without delay is the cost

for 2023. The delayed scenario assumes that the airport has a maintenance budget for 2023 and plans to delay for 2 and 5 years after 2023 to determine the impact on the total maintenance cost. The research team used an inflation rate of concrete derived from the historical cost index of BLS. The team also did not consider the discounted rate to convert the total maintenance cost into net present value in delayed scenarios.

The results show that the total concrete pavement maintenance cost of the airport increases significantly when the PCI values of the pavement decrease. The 5-year delayed maintenance cost of a concrete pavement with a PCI value of 90 is $1,480,088 compared to $5,777,693 for pavements with a PCI value of 80, and $18,260,362 for pavements with a PCI value of 70. Therefore, the PCI values of concrete pavement should be considered when delaying maintenance because they significantly impact the total maintenance cost.

Figure 5-6 shows an increasing trend in the maintenance cost of concrete pavements based on their PCI values. The analysis results show that the percentage the maintenance cost increases for delayed scenarios compared to the base maintenance cost is dependent on the PCI values of the pavement. For the concrete runway pavement with a PCI value of 80, the 2- and 5-year delayed maintenance cost percent increment is higher than the runway pavements with PCI values of 90 and 70. The percentage increment of the pavement with PCI value 80 is 377% when delayed for 5 years compared to its base cost. This analysis shows that there are significant consequences when an airport delays maintenance of its concrete runway pavements. For pavement with a PCI value of 70, the percentage increase of the total maintenance cost will reach 286% of its base maintenance cost when delayed by 5 years. For concrete pavements with a PCI value of 90, the total maintenance cost increases to 72% and 249%, when delayed for 2 and 5 years, respectively.

Results of Delaying Maintenance on the Asphalt Runway Pavement of an Airport

The same hypothetical case study project was considered with asphalt runway pavement. All variables were the same as the concrete runway pavement. Figure 5-7 shows the change in total maintenance cost of the asphalt runway pavement with PCI values of 70, 80, and 90 for 2- and 5-year delayed scenarios. Similar to the concrete runway pavement, the total maintenance cost of

asphalt increases significantly when the maintenance is delayed for 2 or 5 years for pavements with PCI values of 70 and 80, compared to a PCI value of 90. For asphalt runway pavement with a PCI value of 70, the total maintenance cost increases significantly compared to its base cost. The base maintenance cost of the pavement with a PCI value of 70 is $3,815,880 but increases by 132% and 417%, respectively, when it is delayed by 2 and 5 years. These results show that the increase in total maintenance cost depends on the PCI value or age of the asphalt runway pavement.

Figure 5-8 shows the percentage increase in maintenance cost of asphalt runway pavement compared to base cost when the maintenance is delayed for 2 or 5 years. The analysis shows that the percentage increase in total maintenance cost can be seen in all three types of pavements based on their PCI values. However, when the PCI value of asphalt runway pavement is low (70), the percentage increase in maintenance cost is not significantly higher when maintenance is delayed for 2 or 5 years compared to runway pavement that has a PCI value of 90 or 80. For pavement with a PCI value of 70, the base maintenance cost without delay is already high, so the 2- and 5-year delay costs compared to base cost are not significantly different. In absolute dollar values, the 2- and 5-year delay maintenance cost of pavement with a PCI value of 70 is more than the asphalt pavement with PCI values of 90 and 80. When the PCI value of asphalt concrete is 80, the maintenance cost increases by 784% compared to its base cost when it is delayed by 5 years.

Intended Use of the Spreadsheet Tool

The spreadsheet tool (found in Section 2.1 of the Quick Guide) results showed that, when the PCI value of asphalt and concrete pavement is 70, the 2- and 5-year delay in maintenance cost increases significantly. Thus, this spreadsheet tool should generally be used for PCI values above 70 because maintenance becomes less effective, and rehabilitation is usually needed as

the pavement falls below PCI values of 65 or 70. That is why there is a big difference in delayed maintenance cost for a PCI value of 90/80 versus 70. Airports that delay maintenance when the PCI value is 70 need to pay for a mill and inlay instead of preventive maintenance.

5.2 Airfield Markings

Seven steps similar to runway pavement are used to determine the impact that delayed maintenance of airfield markings has on the total maintenance budget. Figure 5-9 shows the framework for calculating the consequence of delayed maintenance on runway markings. The steps involved in calculating the consequences of delayed maintenance are described below.

5.2.1 Establishing Asset Inventory

Airport asset managers collect pavement marking inventory related to types of runway markings, length, and width, outlining the spacing between the markings. FAA AC 150/5340-1M—Standards for Airport Markings discusses the various types of runway and taxiway markings and their dimensions and spacing provided in airport runways. This document describes six types of runway markings:

1. Designation markings,
2. Centerline markings,
3. Threshold markings,
4. Aiming point markings, 5. Touchdown zone markings, and
5. Edge line markings.

Figure 5-10 shows these runway markings and their locations along the runway pavement. FAA AC 150/5340-1M documents contain the number and size of the runway markings. Based on the minimum requirements of each marking, airports can determine the total area and record it in their asset inventory database.

The runway markings asset inventory should consist of the date the marking was repainted and the types of materials used. Generally, water-based or thermoplastic colors are used for runway and taxiway markings. Asset managers should record the total area of runway markings based on the types of runways. The purpose, location, color, and characteristics of these runway markings are described below.

Designation Markings

The purpose of a designation marking is to identify the runway endpoint. Runway landing designator marking(s) must be located within a certain distance from the runway threshold markings as shown in Figure 5-10. The color of this marking is generally white, and the color must be enhanced using certain techniques. A runway landing designator marking consists of a one- or two-digit number. When parallel runways exist, the number is supplemented with a letter. For more information, please refer to FAA AC 150/5340-1M.

Centerline Markings

The purpose of a runway centerline marking is to identify the physical center of the runway width and provide alignment guidelines to pilots during takeoff and landing operations. It is located along the physical center of the runway width and spaced between the runway landing designation markings as shown in Figure 5-10. The color of the runway centerline is white. A runway centerline marking consists of a line of uniformly spaced stripes and gaps of uniform width. The stripes are 120 feet in length and the gaps are 80 feet in length. The minimum width of the stripes is 36 inches for precision runways, 18 inches for non-precision runways, and 12 inches for visual runways.

Threshold Markings

A runway threshold marking, commencing 20 feet from the actual start point of the runway threshold, closely identifies the actual beginning point of the runway threshold used for landings. It starts 20 feet from the starting point of the runway threshold as shown in Figure 5-10. Its marking color is white, and it consists of a longitudinal striped pattern of uniform dimensions spaced symmetrically on the runway centerline. The runway width determines the number of longitudinal stripes and their spacing. Table 5-7 shows the number of stripes based on the width of the runway.

Aiming Point Markings

The main purpose of aiming point markings of the runway is to provide a visual aiming point for landing operations. It is located along the physical center of the runway width and spaced between the runway landing designation markings (Figure 5-10). It consists of a line of uniformly spaced stripes and gaps of uniform width. The markings are 120 feet in length, and the distance between them is 80 feet. The minimum width of the stripes is 36 inches for precision runways, 18 inches for non-precision runways, and 12 inches for visual runways. Aiming point markings are white.

Table 5-7. Number of runway threshold stripes for standard runway widths.

1. Layers of paint from older markings,
2. Rust discoloration,
3. Algae growth,
4. UV damage,
5. The position and dimension of existing markings,
6. The alignment of existing markings for standard compliance, and
7. The composition of existing material/coatings and compatibility with specified materials.

The FAA has developed a method for quickly and accurately evaluating paint markings. A manual method can be used to evaluate smaller surface markings. The FAA has developed an automated method for evaluating larger surface markings over a vast airport area. In addition, the method establishes a threshold pass/fail limit for white and yellow paint (Speidel et al. 2008). The runway markings can be evaluated in three ways:

1. By checking the retroreflectivity with a retrometer.
2. By checking the chromaticity (paint pigmentation) with a colorimeter or comparing it to color chips.
3. By using a transparent grid to inspect the coverage uniformity of the entire (remaining paint) markings.

Most airport asset managers inspect runway markings to check the aforementioned characteristics of the markings to maintain airport safety. However, no airport has developed a process to categorize the marking conditions (Excellent, Good, Fair, and Poor) to determine the runway markings’ deterioration trend. Every airport performs visual inspections, and some use the retroreflectivity measurement instrument to check visibility. These condition data are generally kept along with asset inventory data. It is also required to record the types of paint used, either water-based or thermoplastic, to paint runway markings. The FAA has authorized the use of thermoplastic paint in taxiways. On runways, only waterborne white paints are allowed.

5.2.3 Identifying and Updating Maintenance and Replacement Activities and their Unit Costs

Markings need to be maintained in order to increase their life. Maintenance seeks to keep markings from discoloration due to rust, contamination, rubber deposits, and algae growth, so that the retroreflectivity of the markings will remain in excellent condition. The maintenance activities performed on airfield markings are:

1. Cleaning the markings to remove rust, contamination, rubber deposits, and algae growth.
2. Repainting the markings.
3. Maintenance activities to keep the level of retroreflectivity within a required limit.

Most airports have in-house personnel to perform marking maintenance. If major repainting or replacement needs to be done, contractors are hired. The airport needs to keep a cost database of maintenance activities to be performed on markings. If this maintenance work is done in-house, then the labor hours and materials spent need to be collected annually to estimate a maintenance budget with and without delays. Generally, waterborne airfield paints last for about 2–3 years, and thermoplastic paints last for 4–5 years if regularly maintained (Chang et al. 2017). Waterborne and thermoplastic markings do not result in a major difference in maintenance cost, however, replacement costs can vary greatly.

A case study project collected the unit cost of replacing and maintaining waterborne and thermoplastic markings. The contractor’s bid cost of runway markings was used to determine the total maintenance cost of the markings. The waterborne and thermoplastic markings replacement costs were derived from the FHWA website, which calculates the cost of painting the

roadways (FHWA 2005). Those costs were adjusted to the 2021 base cost. Table 5-8 shows the waterborne and thermoplastic maintenance and replacement costs.

5.2.4 Determining the Marking Failure Probability with Regular Maintenance

The research team collected data on the average life of the waterborne and thermoplastic markings but was not able to collect any data on the deterioration pattern of runway and taxiway markings. The literature has shown that using Weibull distribution can help to estimate the deterioration of markings (Chang et al. 2017). The airfield marking deterioration model used in this study is based on the age of the markings, because the team could not retrieve the condition data from the airports. This age-based model estimates the remaining life of the pavement markings from historical records. The team could not use a condition-based approach to develop reliable deterioration models because it requires periodic condition assessment data. To use Weibull distribution to determine the probability of airfield marking failures, the shape and scale parameters need to be determined (Pham 2023). Equation 5-3 shows the cumulative probability of failure based on Weibull distribution.

f represents failure, γ represents the shape parameter, and α is a scale parameter. In the above equation, the location parameter is 0. Many probability distributions are not a single distribution, but a family of distributions. The shape factor shows the types of probability distributions. These distributions are particularly useful in modeling applications, since they are flexible enough to model a variety of datasets. Depending on the different values of the shape factor, the probability distribution differs. Figure 5-11 shows the probability distribution for shape factors of 0.5, 1, 2, and 5. A shape factor of about 2 will show skewed distribution to the right. A scale parameter, sometimes called characteristic life, is related to the mean time to failure (Galar and Kumar 2017). In Weibull analysis, α is defined as the time at which 63.2% of components under analysis will have failed (Pushpa et al. 2006).

In the highway asset failure probability distribution, the shape factor is taken as 2; therefore, the team also used a shape factor of 2 to determine the failure probability of airfield markings (Chang et al. 2017). The scale factors for white waterborne and thermoplastic markings were selected as 1.3 years and 3 years because the lives of white waterborne and thermoplastic were 2–3 years and 5–6 years, respectively. Interviews with the airport asset managers during data collection confirmed that.

Table 5-9 shows the probability of failure of white waterborne runway markings derived using Weibull probability distribution. The results demonstrate that, with normal deterioration, white waterborne markings must be replaced entirely by the end of the third year.

Table 5-8. Maintenance and replacement costs used for runway markings.

due to a lack of regular maintenance. Table 5-11 shows the cumulative failure probability for white waterborne runways and thermoplastic taxiway markings assuming no maintenance was conducted. The scale factors for white waterborne and thermoplastic markings were selected as 1 and 2 years, respectively. The probability distribution results showed that the white waterborne markings need to be replaced after 2 years and the thermoplastic markings need to be replaced after 3 years due to lack of maintenance.

5.2.6 Estimating Marking Maintenance Budgets without Delayed Scenarios

After determining the types of markings used in runways or taxiways, the total area of markings to be maintained and replaced can be determined using the cumulative failure probability based on the age of the markings. The percentage of white waterborne marking areas to be replaced each year can be calculated using the values in Table 5-9. The replacement of markings will also depend upon the age of the markings. For example, if the runway marking’s area is 1,000 square feet, and its age is 1 year, then the cumulative probability of waterborne white markings failure in year 2 (the next year) will be 83.10%. This means that about 831 square feet of markings need to be replaced, and the rest of the markings can be regularly maintained without replacement. Similar estimates can be performed if thermoplastics are used in taxiway markings by using the cumulative probability values provided in Table 5-10, based on the age of the markings.

Upon estimating the area of the markings to be maintained and replaced, the cost of regular maintenance can be determined by multiplying the area by the unit cost of maintenance and replacement. The research team developed a spreadsheet tool to calculate a regular maintenance budget, as well as delayed maintenance costs.

5.2.7 Estimating Marking Maintenance Budgets with Delayed Scenarios

The research team used procedures described in the previous section to estimate the maintenance and replacement cost of markings for delayed scenarios. The difference was the higher cumulative failure probability of markings due to neglected airfield marking maintenance. Delaying maintenance is not encouraged, because the team has not considered airplane safety when marking maintenance and replacement are delayed. The spreadsheet tool in Section 2.2 of the Quick Guide provides the dollar amounts that airports will need to spend when the maintenance and replacement of the airfield markings are delayed by a specific number of years. The tool uses the historical rate of inflation and provides the option to select the marking inflation factor, as the inflation of the future year is difficult to predict. The historical paint and coating manufacturing price index shows that the average inflation of the paints is about 3.23% per year (FRED 2022a). The marking maintenance and replacement cost data are from 2021. However, when the airport needs to use this spreadsheet tool in the future, the cost data will be automatically adjusted based on the budget

Table 5-11. Weibull distribution for white waterborne and thermoplastic markings without maintenance.

preparation year, and the default inflation will be used to calculate the delayed maintenance cost. The airport can also enter its paint inflation rate when calculating the delayed maintenance costs.

5.2.8 Reporting the Impact of Marking Delayed Maintenance and its Consequences

The tool developed by the team was used to determine the impact of delayed maintenance on markings. A hypothetical airport case study was developed to estimate the impact of delayed maintenance of markings on total maintenance and replacement cost (Table 5-12). The delayed scenarios are 1 and 2 years, and the runway and taxiway markings are new, 1, or 2 years old.

Case Study Results of the Consequences of Delaying Maintenance on Airfield Markings

Results of Delaying Maintenance on White Waterborne Runway Markings

Figure 5-12 shows the impact of delaying maintenance on white waterborne runway markings. The maintenance cost increases as the age of the runway markings increases. When the white waterborne runway markings have been recently replaced, the delayed maintenance cost is higher compared to 3-year-old markings. The data analysis shows that the maintenance cost of newly installed runway markings will more than double when delayed by 1 year. If the maintenance is delayed for 2 years, the total maintenance cost does not change much because delaying 1 year of maintenance will require more than 98% of the markings to be replaced (Table 5-11). When the team analyzed runway white waterborne markings of ages 1 and 2 years, the impact of delayed maintenance seemed minimal, because the markings need to be replaced as soon as possible in normal deterioration conditions. Based on Table 5-11, if the runway waterborne markings are 2 years old, then the next fiscal year, the replacement percentage will be 100% based on delayed maintenance deterioration models. Delaying these failed runway markings will not have any effect on total replacement cost, but it can jeopardize airplane safety. In the case of runway markings, the effect of delaying maintenance is minimal because all airports replace their runway markings every 3 to 4 years.

Figure 5-13 shows the increase in total maintenance cost for three types of white waterborne runway markings based on the age of the markings. It clearly shows that, when the runway markings are new, the delay in maintenance of the markings has a significant impact on the total maintenance cost. However, after the runway markings start aging, the maintenance delay does not have a significant impact. This is because white waterborne markings are required to be replaced every 2 to 3 years. It is critical that airport asset managers consider airplane safety before delaying

Table 5-12. Case study data of airport runway and taxiway markings.

maintenance or replacing runway markings. Any decision made by airport authorities related to delayed maintenance can have serious repercussions.

Results of Delaying Maintenance on Thermoplastic Taxiway Markings

The spreadsheet tool (found in Section 2.2 of the Quick Guide) developed was used to determine the impact of delayed maintenance on the total maintenance cost of thermoplastic taxiway markings. The research team used the hypothetical airport project data shown in Table 5-12. Similar to the white waterborne runway markings case study, the thermoplastic taxiway markings were assumed to be new, 1 and 2 years old. To determine the impact of delayed maintenance, the maintenance was delayed for 1 and 2 years. Figure 5-14 shows the increase in total maintenance cost of the thermoplastic taxiway markings (30,000 square feet) for new, 1-year, and 2-year-old markings, assuming the maintenance was delayed for 1 and 2 years. The base cost shows the total maintenance cost required to maintain and replace the thermoplastic taxiway markings when the markings are recently painted, 1 year, or 2 years old is $15,316, $38,798, and $64,105, respectively. The delayed scenario for 1 and 2 years shows that the total maintenance cost increases significantly compared to the base cost. As the taxiway markings’ age increases, the total maintenance cost for delayed scenarios does not increase at a higher rate due to the reasons mentioned above.

Figure 5-15 shows the percentage increase in total maintenance and the replacement cost of thermoplastic taxiway markings based on the age of the markings. The graph shows that the total cost increases 456% when the markings are new and delayed by 1 year. However, delaying maintenance by another year will not have a significant impact, because it will only increase the cost by 115% compared to the 1-year delay. The reason is that the life of thermoplastic markings is about 3 to 4 years when the markings are not regularly maintained. By the end of 2 years, more than 83% of the markings must be replaced (See Table 5-11). Delaying another year will increase the marking replacement cost by 15%, which has an insignificant impact on the total maintenance and replacement cost. If the markings are 1 year old, the cost to maintain them in the 2nd year

will be comparatively high. This is because the failure probability distribution shows that 35.9% of the thermoplastic markings need to be replaced in the 2nd year, which is 25.4% higher than new markings (See Table 5-10). In cases with 1- and 2-year-old markings, delaying the maintenance and replacement by 1 or 2 years will not have a significant increase in the total cost due to the reasons described above.

5.3 Runway Lighting

Runway lighting is critical infrastructure in an airport. These lights assist the pilots in landing the planes safely at night, so these lights should be maintained frequently. If the lighting maintenance is delayed, then night flights need to be canceled because planes cannot land without these lights. The framework and tools developed in this research can hypothetically determine the effects of delaying the maintenance of runway lights on the budget. Figure 5-16 shows the framework for calculating the cost impact of delayed maintenance on runway lighting. The framework is described below in detail.

5.3.1 Establishing Asset Inventory

This study focuses on lighting provided around runways. The spreadsheet tool that was developed does not cover any lighting provided in the apron or taxiways. FAA AC 150/5345-46E describes various types of runway lights. The major types are (1) runway edge lights, (2) runway centerline lights, (3) runway approach lights, (4) runway end lights, (5) runway threshold lights, and (6) touchdown zone lights. There are other lights provided around runways such as the Medium Intensity Approach Lighting System, Runway Status Lights (RWSL), Takeoff Hold Lights, and Runway Intersection Lights. Figure 5-17 shows the layout of runway lighting.

Table 5-13 shows lighting color and spacing in the runways. Asset managers need to keep inventory of these lights along with the electrical line distribution, the record of the transformer,

voltage regulators, main switchboards, etc., to calculate the accurate maintenance and replacement cost. Therefore, the length of the underground wiring, locations of the transformer, voltage regulators, switch boxes, and connectors must be collected to determine the maintenance cost of these systems.

5.3.2 Performing a Condition Assessment

One of the asset manager’s most important jobs is to perform condition assessments of the runway lighting systems. Asset managers need to collect the condition of light fixtures and electrical lines and ideally categorize them by level, e.g., excellent, good, fair, and poor. Most of the airports the research team contacted don’t have these data because the asset managers have not collected the data and entered it into the system. However, the airports inspect the light fixtures and electrical distribution system and conduct preventive maintenance annually, if necessary. The condition of lighting systems generally deteriorates due to environmental factors, like sunlight, rain, and wind. The light fixtures also degrade naturally. This includes bulbs, electrical conduits, transformers, connectors, and switch systems. In terms of runway lighting, the airports have not collected detailed condition assessment data. To estimate the maintenance and rehabilitation cost of the runway lighting and conduits, these data play a valuable role in determining reliable deterioration models. However, most of the airports have inventory data of the number of light fixtures, types of fixtures [LED or high-pressure sodium (HPS)], condition of the transformer, switching systems, and fixture connectors. Airports had not used these data to come up with a systematic method of categorizing the condition of runway lighting systems. Generally, the light fixtures used are either LED or HPS. Airports change the lighting fixtures as a part of their maintenance program. However, the replacement of electrical conduits and distribution lines rarely occurs. The maintenance of transformers, connectors, and switching systems is regularly performed by either in-house electricians or outside electrical contractors. ACRP Report 148: LED Airfield Lighting System Operation and Maintenance highlights inspection processes to determine the airfield lighting system conditions. According to ACRP Report 148, the airfield lighting system inspection should consist of the following:

• Visual and physical inspection,
• Electrical testing,
• Photometric testing, and
• System burn-in.

The type of power feed supplying the sign and its nameplate data should be verified. The field location and orientation of all the airfield lights should be inspected in terms of whether the exterior and interior lights are clean and clear of debris; the power supply is in a sealed enclosure or is encapsulated for its protection; the light covers and frame are free of scratches, cracks, or breaks; and all bolts and tethers are properly installed and secured. The components of lighting and electrical distribution systems should be inspected regularly to avoid breaking. These include connectors, grounding, spacers, top extensions or flange rings, bolt lengths, transformers, cable lengths, and conduit ends, among others.

5.3.3 Identifying and Updating Maintenance and Replacement Activities and their Unit Costs

Because runway lighting systems are vital for airplane safety, all of the airports spent the required budget to maintain them. The airports also performed regular maintenance work on runway lighting systems. ACRP Report 148: LED Airfield Lighting System Operation and Maintenance highlighted

some of the maintenance activities to be conducted on the runway lighting systems to keep these lights in working condition. Some of these activities include:

• Inspect for outages and repair as necessary,
• Check the cleanliness of lenses,
• Perform photometric testing (HIRL) and check light alignment and orientation,
• Re-align lights as needed,
• Clean fixtures and sockets,
• Check light elevation,
• Check for moisture in lights,
• Inspect fixture for rust and deterioration,
• Check lamp fitting and clean contacts,
• Check gaskets, and
• Remove snow and/or vegetation from around lights.

ACRP Report 148: LED Airfield Lighting System Operation and Maintenance found that about 57% of airports surveyed used their in-house electricians to maintain their airfield lighting systems. The study also recommended inspection methods of airfield lighting systems to conduct efficient maintenance work. Along with maintenance activities, the airport must collect and update the following costs of the runway lights to calculate the required maintenance cost:

• LED light fixture cost,
• HPS light fixture cost,
• Maintenance cost (lamp replacement labor and materials),
• Refurbishment cost, and
• Maintenance cost of electrical conduit (labor and materials).

After determining the maintenance activities to be performed for the runway lighting system, the asset manager must determine the unit cost for maintenance and replacement. During the data collection phase, the research team collected the maintenance and replacement labor and parts cost data. The team used these data to determine the unit cost of maintenance and replacement. The airports tend to use HPS or LED runway light fixtures, therefore the research team collected the cost of these lights and verified using the RSMeans Cost Guide (2021). Table 5-14 shows the maintenance cost calculations using the labor hours the airports reported.

The replacement cost of the lighting systems was also collected from the airport case study and verified with the RSMeans Cost Guide. The research team gathered the replacement costs of HPS and LED light fixtures from an online search and verified them with the RSMeans Cost

Table 5-14. Unit maintenance cost calculations for airfield lighting systems.

Table 5-15. Replacement costs for airfield lighting systems.

Guide. Table 5-15 shows the replacement cost of the lighting system per foot, HPS, and LED runway light fixtures.

5.3.4 Determining the Runway Lighting Failure Probability with Regular Maintenance

When collecting data regarding the airfield lights, the research team found that most of the airports do not rate the conditions of their airfield lighting systems as excellent, good, fair, or poor. Therefore, to determine the deterioration trend of light fixtures, the team considered the Weibull probability distribution. However, for the electrical distribution system (conduit), failure can be calculated using the reliability theory. Reliability is defined as the probability that a component or system will operate according to its specifications for a given period. Reliability is a function of time. For the failure probability distribution of runway light fixtures, the research team used the Weibull distribution. NCHRP Research Report 859: Consequences of Delayed Maintenance of Highway Assets used the Weibull distribution to determine the failure probability of highway LED and HPS lighting. The team used similar processes to determine the cumulative failure probability distribution of the runway LED and HPS light fixtures. Shape factors of 5 and 14 were used for HPS and LED fixtures, respectively, to determine the failure probability. Failure probability is also dependent on the number of hours the airports use these lights. Generally, the HPS fixtures last for 4 years, resulting in a total of 14,600 hours (considering 10 hours per day and 365 days in a year). LED fixtures generally last for 15 years, which is equivalent to about 54,750 hours. Considering that 63% of the HPS light fixtures will fail by 7,000 hours, the cumulative failure probability distributions were calculated in Table 5-16.

Considering that 63% of the LED light fixtures will fail by 45,000 hours, the cumulative failure probability distributions are calculated and shown in Table 5-17.

It is also necessary to determine the failure probabilities of electrical conduit systems. In electrical engineering, the system and component failure rates can be determined by using the reliability

Table 5-16. Weibull distribution for HPS light fixtures.

Table 5-17. Weibull distribution for LED light fixtures.

theory. The TASA Group (n.d.) defines reliability as “the probability that a component, subassembly, or system will operate according to specifications for a given period of time (t).” Reliability is the function of time (t) and can be represented by R(t) and calculated using Equation 5-4.

For the airport electrical system, the team used 3,650 hours per year considering 10 hours per day of usage. Using one failure per million hours (FPMH), the value of λ can be taken as 0.000001 FPMH. This reliability value is for a single component system. If the electrical system has multiple components, the reliability can be calculated using Equation 5-5.

In airfield electrical systems, the number of components in the system is assumed to be five. Those components are transformers, switchboards, connections to airfield lights, connections to airfield signs, and voltage breakers. Equation 5-5 calculates the reliability of an electrical system for each year. The calculation results are shown in Table 5-18. The failure probability can be calculated by subtracting the reliability values from 1, and those results, up to 15 years, are also shown in Table 5-18.

Tables 5-16 to 5-18 determine the failure probability of HPS and LED light fixtures as well as electrical systems, while calculating the total maintenance cost of runway lights and electrical conduit systems. The airfield lights and electrical conduit systems deteriorate, even when regular maintenance is performed on these components. So, the deterioration models used will address the failure probability of light fixtures and electrical systems for normal conditions.

5.3.5 Determining the Runway Lighting Failure Probability with Delayed Maintenance

There are no reliability and failure probability models for electrical systems that are not regularly maintained. There are also no data available to determine the deterioration trend of light fixtures and

Table 5-18. Reliability and failure probability of electrical conduit systems.

electrical systems. The research team assumed that the failure probability of the regularly maintained runway lights and electrical system is less than that of the systems that are not regularly maintained. The research team also assumed that the HPS and LED light fixtures’ scale factors would be different than the scale factors of regularly maintained light fixtures. Assuming that the scale factors of HPS and LED light fixtures are 5,000 and 25,000 hours, respectively, the cumulative probabilities for these light fixtures are calculated in Tables 5-19 and 5-20. Table 5-19 shows that the HPS light fixtures will last only 2 years and in the 3rd year will need a complete replacement. Table 5-20 shows that LED light fixtures can last for 7 years before needing replacement.

Similar to the light fixtures, the research team assumed that the deterioration of the electrical system would also be faster for a system that is not regularly maintained, compared to a maintained system. In the case of electrical systems, the systems lacking regular maintenance deteriorate at twice the rate of a well-maintained system. In Table 5-21, the probability of failure

Table 5-19. Weibull distribution for HPS light fixtures with delayed maintenance.

Table 5-20. Weibull distribution for LED light fixtures with delayed maintenance.

Table 5-21. Failure probabilities of electrical systems with delayed maintenance.

increases by about 1.7% to 1.8% every year. Therefore, the research team has concluded that the failure probabilities of systems not regularly maintained will increase by 3.5%. Table 5-21 shows the electrical systems’ failure probabilities for every year if the system is not regularly maintained.

5.3.6 Estimating Runway Lighting Maintenance Budgets without Delayed Scenarios

The total maintenance cost of the runway lighting can be calculated by determining how many light fixtures are needed and the length of the electrical system that needs to be replaced, based on their failure probabilities and the cost of maintaining the remaining light fixtures and electrical conduits. Therefore, the normal probability of failure estimated in Section 5.3.4 can be used to determine the number of runway lights and length of the electrical circuits that need to be replaced. Then, the unit cost of light fixtures and electrical conduits can be multiplied to find the total cost of replacement. The total maintenance cost can be calculated by multiplying the unit cost of maintenance by the number of light fixtures, and length of electrical conduits to be maintained every year. The accurate unit replacement cost of these light fixtures and the number of fixtures to be replaced needs to be accurately estimated to find the precise replacement cost. To determine the replacement cost of electrical conduits, the estimated length of the electrical system should be calculated accurately, and the cost per unit of length needs to be precise to find a good estimate of the total replacement budget. Similarly, the maintenance cost per unit of light fixtures and the per unit length of the electrical conduit need to be collected to calculate the accurate maintenance cost of the airfield lights. The research team collected these cost data from the airports. However, not all of the cost data were available, therefore, some cost data were gathered from the RSMeans Cost Guide as well as online databases. The inflation factor for lighting maintenance and light fixtures was derived from the cost indices of Federal Reserve Economic Data (FRED). According to this database, the average inflation per year for electrical contractors is 2.33% (FRED 2022a). For HPS and LED light fixture replacements, the average inflation is estimated at 2.72% per year (FRED 2022c).

5.3.7 Estimating Runway Lighting Maintenance Budgets with Delayed Scenarios

Similar to the process described for regular maintenance budgets without delayed scenarios, the research team used Tables 5-19 to 5-21 to determine the total maintenance and replacement

cost of runway lights in delayed scenarios. For this purpose, the probabilities of failure for HPS and LED light fixtures are given in Tables 5-19 and 5-20. For the electrical systems, the failure probabilities were taken from Table 5-21. Once the failure probabilities were determined, the cost of HPS and LED light fixture replacement was calculated by their unit cost. Similarly, for the electrical system, the cost of replacement was calculated by multiplying the unit cost of electrical system replacement with the length of the electrical conduit to be replaced due to delayed maintenance. Also, the maintenance cost of the surviving HPS, LED light fixtures, and electrical systems can be calculated by multiplying the unit cost of maintenance with the number of light fixtures and length of electrical conduits to be maintained. The total cost of maintenance and replacement was calculated considering an inflation rate of 2.33% for maintenance and 2.72% for replacement work. However, the users can input their own inflation rate to calculate the delayed maintenance costs.

5.3.8 Reporting the Impact of Runway Lighting Delayed Maintenance and its Consequences

The spreadsheet tool the team developed was used to determine the impact of delayed maintenance on runway lighting. A hypothetical airport case study was developed to estimate the impact of delayed maintenance of runway lighting on total maintenance and replacement costs. Table 5-22 shows the hypothetical airport data to determine the impact of delayed maintenance of runway lighting. The delayed scenario was taken as 1 and 2 years, as the HPS light fixtures last only 3 to 4 years. For LED light fixtures, the delayed scenario was considered for 2 and 5 years. The spreadsheet tool to determine the impact of delayed maintenance of runway lights has an option to choose delayed scenarios from 1 to 10 years. The age of HPS light fixtures can be new, 1, or 2 years old. For LED lights, the age can be new, 5, or 10 years old. The tool can also convert future costs into present costs using various discount rates.

Case Study Results of the Consequences of Delaying Maintenance on Runway Lighting

Results of Delaying Maintenance on HPS Runway Lighting

The research team used the spreadsheet tool to determine the impact of delayed maintenance on the total maintenance and replacement costs of HPS runway lighting. The scenarios in which the airport installed new HPS lights less than 2 years prior are the only ones that were considered

Table 5-22. Case study data of airport runway lighting.

since HPS lights do not have more than 3 years of life. The delayed scenarios were considered for 1 and 2 years. Figure 5-18 shows the total maintenance and replacement cost of runway lights in the hypothetical case study considered with no delay, a 1-year delay, and a 2-year delay, based on the age of the runway’s HPS light fixtures. The total maintenance and replacement cost of runway lights will increase significantly when delayed 1 year for newly installed HPS light fixtures. However, the delay in 2 years will not have a high impact on the total maintenance and replacement cost, because the failure rate of HPS light fixtures in delayed scenarios is 99.9% and 100%, respectively (Table 5-19). Similarly, when it is assumed that the age of runway lighting with HPS light fixtures is 1 and 2 years old, the total base cost of maintenance and replacement will not be significantly different because the failure probability of HPS light fixtures will reach 70.9% and 99.9%, respectively in the following years (Table 5-16). Due to the low cost of HPS light fixtures, there is no significant difference between base cost scenarios of HPS bulb fixtures aged 0, 1, and 2 years. If the maintenance is delayed for 1 and 2 years for 1- and 2-year-old HPS light fixtures, the total maintenance and replacement cost will be similar to the newly installed HPS light fixtures.

A similar analysis was conducted to find the percentage increase in total maintenance and replacement costs of runway HPS light fixture lighting for new, 1-year, and 2-year-old fixtures in delayed scenarios. Figure 5-19 shows that the age of HPS light fixtures will not have an impact on the total and maintenance cost of the runway lighting due to the reasons mentioned above. Because HPS light fixtures need to be replaced every 2 to 3 years, delaying their maintenance does not make sense. It is suggested that the airport replace the HPS light fixtures of their runway lighting every 2 to 3 years.

Results of Delaying Maintenance on LED Runway Lighting

The research team used the spreadsheet tool to determine the impact of delayed maintenance on total LED runway lighting maintenance and replacement costs. Figure 5-20 shows the regular and delayed maintenance and replacement costs of LED light fixtures. The total maintenance and

replacement cost for LED runway lighting increases when maintenance is delayed. However, the total maintenance and replacement costs of 5-year-old and 10-year-old LED lights do not increase based on age. When the maintenance is delayed by 5 years for these light fixtures, the probability distribution of delayed maintenance will reach 100% failure at 8 years (Figure 5-20).

A similar analysis was conducted to determine the percentage increase in total maintenance and replacement costs of runway LED light fixtures for new, 5-year, and 10-year-old fixtures in 1- and 2-year delayed scenarios. Figure 5-21 shows that the age of LED light fixtures will impact the total maintenance and replacement costs of the runway lighting due to the reasons mentioned above. Because the LED light fixtures tend to last around 8 years in a delayed maintenance scenario, the total maintenance and replacement cost will be highest when 5-year-old light fixtures are delayed up to 5 years.

5.4 Airfield Signs

There are various types of signs used in runways, taxiways, and aprons of airports. These signs play an important role in guiding pilots to navigate properly during takeoff, landing, and taxing. These signs should be maintained regularly and need to be replaced as required. Old and faded signs can confuse pilots and other airport workers, which may lead to an accident. Therefore, the important tasks of airport asset managers are to keep a record of sign inventory, track their condition, identify their maintenance activities and unit costs, and prepare a maintenance and replacement budget for the signs each year. Signs placed in runway areas are particularly crucial, and delaying their maintenance should be considered carefully to avoid jeopardizing flight safety. Signs provided in taxiways and other areas can be delayed, but the delay’s impact on the safety and operation of the airplanes must first be determined. The research team prepared a

framework to determine the impact of delayed airport sign maintenance on total airport maintenance and replacement costs. This framework is shown in Figure 5-22. The framework consists of various phases that asset managers need to perform to determine the impact of delayed airport sign maintenance on the total maintenance and replacement costs for the airport. Furthermore, it is not logical or reasonable to convert these impacts into dollar equivalents. The following sections describe each phase.

5.4.1 Establishing Asset Inventory

All airport asset managers need to keep track of airfield signs used in their runways and taxiways. According to FAA AC 150/5345-44K – Specification of Runway and Taxiway Signs, the signs provided in airport runways and taxiways can be lighted or unlighted (FAA 2022d). Figure 5-23 shows the assemblies of typical stop and yield signs used in airport runways. The use of specifications in this AC is mandatory for runway and taxiway signage projects funded under the AIP or with revenue from the PFC program. Based on the specifications, there are six types of signs provided on runways and taxiways. They are:

1. Direction, destination, and boundary signs.
2. Mandatory instruction signs.
3. Taxiway location signs.
4. Runway distance remaining signs.
5. Taxiway ending marker signs.
6. One-half distance remaining signs.

The FAA AC provides advice for the sizes of sign legend panels. It discusses various styles, classes, and modes of signs. The AC provides specific guidelines related to message elements, message arrays, readability, and sign face elements, including borders, margins, edges, and arrays. It also covers the details of lighted and unlighted signs, including their mounting legs, light powers, luminance, materials, and components.

Airport asset managers need to keep a record of these signs so that the maintenance budget can be calculated accurately. Because there are various types and sizes of signs, all signs within the same category need to be collected and recorded separately. The maintenance and replacement costs of these various signs may differ, and separate records will help accurately estimate their maintenance and replacement costs. The airfield sign inventory needs to be updated every time the signs are replaced or damaged.

5.4.2 Performing a Condition Assessment

One of the important duties of asset managers in the airport is to perform condition assessments of airfield signs every year. This is done so the signs can be maintained and replaced based on their conditions. During data collection of airfield signs, it was found that some airports performed and kept the condition data based on four categories: (1) Excellent, (2) Good, (3) Fair, and (4) Poor. If the signs are in “Excellent,” “Good,” or “Fair” condition, these signs still need maintenance to preserve their conditions or prevent them from deteriorating rapidly. When the conditions of the signs reach the “Poor” category, they should be replaced within the following year. Condition assessment in this category will help asset managers estimate the maintenance and replacement cost of airfield signs accurately. However, it was found during data collection that some, but not all, airports put the condition data of runway and taxiway signs in the four above-mentioned categories. When the signs are inspected, their structural components and information panels need to be rated. If the signs are lighted, then their mounting legs, hardware, electrical circuits, bulbs, panels, electrical power regulator, luminance, sign materials, and

components need to be inspected to make sure that the signs are working properly. FHWA has researched the inspection, maintenance, and repair of highway signs and traffic signals and developed a rating system for sign inspection. Table 5-23 shows the rating system.

5.4.3 Identifying and Updating Maintenance and Replacement Activities and their Unit Costs

During the inspection and condition rating of the runway and taxiway traffic signs, the asset managers need to identify what maintenance and repair activities should be performed to maintain the signs. Some of the maintenance activities to be performed for unlighted signs are (McGee 2010):

1. Sign cleaning,
2. Vegetation control,
3. Anti-theft measures, and
4. Sign support adjustments.

It is necessary to clean the sign face because high air traffic volume may cause the sign to become less visible due to a buildup of dirt, grime, mildew, or mold. During the spring and summer seasons, signs can be partially or fully blocked by vegetation or fast-growing weeds that develop quickly around them. Furthermore, signs are occasionally stolen for any number of reasons. Sign supports are also critical and need to be maintained to keep the sign working properly. Sign supports can be maintained by performing the following activities:

• Ensure the signpost is still firmly placed in the ground.
• Provide additional supports and braces, if necessary.
• Place the signs at the required distance so that an airplane or airport service vehicle may avoid hitting the sign.
• Protect sign supports from soil erosion at the base and the growth of trees around the support.

All of these maintenance and repair activities must be performed in-house or by third-party contractors. After identifying these activities and the necessary frequency, airport asset managers must estimate the labor and parts costs for performing the maintenance activities annually. This unit cost of maintenance and replacement is critical in estimating accurate maintenance costs with and without delayed maintenance.

During the data collection phase, the research team was able to collect the labor hours and money spent on all signs in the airport. Based on these cost data, the team calculated the maintenance cost per sign. The ratio of cost and parts used here is derived from the RSMeans Cost Guide 2022. The rate of the electrician used is based on average Nevada rates. The calculation of maintenance cost per sign is provided in Table 5-24.

Table 5-23. Condition rating of highway signs and signals (FHWA 2005).

data were used in the spreadsheet tool developed to calculate the impact of delayed maintenance on airfield signs. However, the tool is flexible, and users can input their own airport’s unit costs to calculate accurate maintenance and replacement costs with and without delayed scenarios. Table 5-24, in Section 5.4.3, shows the maintenance cost per sign calculation from one airport’s case study data. Also, the replacement costs for specific airport signs are described in that section. These costs, along with the inflation rate, were used to determine regular maintenance and replacement costs with and without delayed maintenance scenarios.

5.4.7 Estimating Airfield Sign Maintenance Budgets with Delayed Scenarios

The impacts of delayed airfield sign maintenance are found by calculating the total maintenance and replacement costs and using a delayed maintenance scenario. To calculate this, the probability matrix of airfield sign condition transitions shown in Table 5-26 was used, and the cost of maintaining the airfield signs was divided into four categories (Excellent, Good, Fair, and Poor). Similarly, the number of airfield signs in the Replacement category was multiplied by the replacement cost with an inflation factor. The tool developed by the team allows the user to delay a specific number of years to find the delay’s impact on the total maintenance and replacement costs of airfield signs. The user can also use different inflation factors than the ones based on historical trends. The tool can assist in converting future maintenance and replacement costs to present costs by selecting various discount rates.

5.4.8 Reporting the Impact of Airfield Signs’ Delayed Maintenance and their Consequences

The research team used the tool to determine the regular maintenance and replacement costs of airfield signs when maintenance is delayed. Table 5-27 shows hypothetical airport case study data and the impact of delayed maintenance of airfield signs on total maintenance and replacement costs. To calculate the regular maintenance and replacement costs with and without delayed scenarios, it was assumed that 36, 32, 30, two, and zero airfield signs were under Excellent, Good, Fair, Poor, and Replacement conditions in the year 2022. The regular maintenance and replacement costs were calculated for the year 2023 without delayed maintenance. The maintenance and replacement costs for years 2025 and 2028 with 2- and 5-year delays were also considered to determine the impact on airport costs.

Case Study Results for the Consequence of Delaying Maintenance on Airfield Signs

Figure 5-24 shows the total maintenance and replacement cost with and without delayed maintenance of airfield direction signs for a hypothetical case study airport. The delayed scenarios

Table 5-27. Case study data of airport signs.

used were 2 and 5 years. The data showed that the maintenance and replacement costs of the airfield signs increased significantly when going from no delay to a 2-year delay. However, the total maintenance and replacement costs do not increase significantly when maintenance is delayed by 5 years. This is because 75% of the total signs (76 out of 100 signs) need to be replaced during the 2-year delay. As a result, delaying by 5 years increases the replacement cost of 24 more signs. The deterioration models with delayed maintenance showed that, when the maintenance is delayed by 3 years, the number of signs to be replaced drastically reduced due to a smaller number of signs left to be maintained.

Figure 5-25 shows the percentage increase in the maintenance and replacement cost of direction signs for the case study project. It shows that the increment percentage of maintenance and replacement cost is higher for a 2-year delay than for a 5-year delay. There was an 83% maintenance and replacement cost increase when the maintenance was delayed by 2 years. However, the percentage increase was not as high when the maintenance was delayed by 5 years.