Miscellaneous

This section lists any additional information not categorizable in a conventional section.

Equivalent Single Axle Loads

Equivalent Single Axle Loads (ESAL) simplifies multi-axle traffice data into a straightforward single-axle form. ESALs has been used by PMED engineers to calculate the effects of axle loads on pavement over time for a very long time. However, PMED no longer uses ESALs in its regular outputs, foregoing it for a more sophisticated, multi-axle spectra. Regardless, ESAL outputs can still be found within the ZIP downloadable.

Figure 867: ESAL Example Text File output

Calculating ESALs

Inputs

The inputs required in PMED are listed below. Example value are shown to provide a reference to the attached spreadsheet.

• Two-way Average annual daily truck traffic (AADTT): This control allows you to define the average annual daily truck traffic (FHWA vehicle classes 4-13) expected over the base year in both directions of travel for your project.
• Percent trucks in design direction: This control allows you to define the percentage of trucks (from the entire two-way AADTT count) that is expected to travel in the design direction. Note that although this value is close to 50 percent, it is not necessarily so especially in cases where truck traffic does not use the same route for the onward and return trips.
• Percent trucks in design lane: This control allows you to define percentage of trucks in the design direction expected to use the design lane (typically the outer right lane).
• Vehicle class distribution (VCD), Vehicle Class growth rate and growth function
• Number of axles per truck/vehicle class for Single, Tandem, Tridem, and Quad axles (APTC)
• Axle load distribution by month, vehicle class, and load category (ALDF)

Note:
Each row must sum to 100

Calculations

Step 7 is the only unique step in calculating ESALs. All other traffic calculations occur for other parts of the output report, so you may be familiar with them already. For more thorough explanation of the steps prior to step 7 please refer to the traffic page.

1. Adjust AADTT for directional and lane distributions
2. Forecast average monthly daily number of trucks
3. Compute average monthly trucks for each vehicle class for the base year (AMDTT)
4. Apply monthly adjustment factors to AMDTT calculated in Step 3
5. Calculate total number of axles for each axle type
6. Calculate the total number of applications for each load category and vehicle class.
7. Calculate ESALs: The ESAL’s are calculated by multiplying the total number of single axles for each load category by the default load equivalency factor (LEF).

LEF Factors

The ESAL’s are calculated by multiplying the total number of single axles for each load category by the default load equivalency factor (LEF). The ESALs for each month, axle type, and load category are accumulated to determine the total ESALS at the end of the design period.

Figure 868: ESAL LEF Flexibles

It should be noted that the PMED predicted values in the “FlexibleESAL” and “ESALs” output files are rounded to the nearest 100,000 trucks. The differences in rounding is not an important factor because PMED does not use ESALs in any of the analysis models.

Figure 869: ESAL LEF Rigid

Obtaining ESAL outputs

1. Download the relevant designs zip file

Figure 870: ESAL - Downloading the ZIP output of a given project

2. Navigate to the output folders

3. For aggregate totals, Look for text file, ESALs.txt

Figure 871: ESAL ESALs.txt

4. For outputs for each axle, look for their corresponding csv file e.g. TandemAxleOutput.csv

Figure 872: ESAL ESALs Axle CSVs