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The LTPP program contains two major experiment types: the General Pavement Studies (GPS) which are comprised of pavement sections constructed before the LTPP program started, and the Specific Pavement Studies (SPS) which are the pavement sections designed and constructed specifically for the LTPP program. Here is a detailed list of the different studies:

• GPS-1: Asphalt Concrete (AC) on Granular Base
• GPS-2: AC on Bound Base
• GPS-3: Jointed Plain Concrete Pavement (JPCP)
• GPS-4: Jointed Reinforced Concrete Pavement (JRCP)
• GPS-5: Continuously Reinforced Concrete Pavement (CRCP)
• GPS-6: AC Overlay of AC Pavement
• GPS-7: AC Overlay of PCC
• GPS-9: Unbonded PCC Overlays on PCC Pavements
• SPS-1: Strategic Study of Structural Factors for Flexible Pavements
• SPS-2: Strategic Study of Structural Factors for Rigid Pavements
• SPS-3: Preventive Maintenance Effectiveness of Flexible Pavements
• SPS-4: Preventive Maintenance Effectiveness of Rigid Pavements
• SPS-5: Rehabilitation of Asphalt Concrete Pavements
• SPS-6: Rehabilitation of Jointed PCC Pavements
• SPS-7: Bonded PCC Overlays on Concrete Pavements
• SPS-8: Study of Environmental Effects in the Absence of Heavy Loads
• SPS-9: Validation of SHRP Asphalt Specification and Mix Design (Superpave)
• SPS-10: Warm Mix Asphalt (WMA) Overlays of AC Pavements
• SPS-11 (Not Initiated): AC Pavement Preservation
• SPS-12 (Not Initiated): PCC Pavement Preservation

Data for studies like Seasonal Monitoring Program (SMP) and Traffic Pool Funded Study (TPFS) were collected on a smaller group of these SPS and GPS sections.

The “Find Sections” filtering feature in LTPP InfoPave gives users the option to select sections based on experiment type, state/province, etc. This filtering is available in various features of InfoPave where data can be selected at the section level. While using those features, you will be able to apply the “Experiment Type” to define the GPS or SPS experiment and “Location” filters to select the required State/Province.

If you are trying to determine the experiment type of a specific section, you can select the “Section Summary Report” under Data and the experiment number is available in the general information header of the report.

The unique identifier for LTPP section consists of a combination of STATE_CODE (2 characters)-SHRP_ID (4 characters) (e.g., 27-0501). The naming convention for SHRP_ID varies based on the experiment type as discussed below:
 
SPS sections SHRP_ID:
 
The SPS sections have two SHRP_ID systems; the first system is applicable for SPS-1 to SPS-9 projects and the second system is applicable from SPS-10 going forward.
 

1. In the first system, the first character should be 0, A, B, C, etc., depending on how many projects of that type exist in a State (e.g., 0XXX, AXXX, BXXX, etc.). The second character for SPS sites is the experiment number (e.g., 01XX or A1XX for SPS-1 projects consisting of SPS-1 sections). For SPS-3 and SPS-4, the 1st character is always alphabetic starting with A and working through the alphabet depending on the number of projects in a State. For example, SHRP_ID (section ID) A310 means the first project of SPS-3.

2. In the second system, the first character should be A, B, C, etc., where the character “A” is assigned to the first project and all test sections located on that project. The second character is the experiment number, where “A” is for SPS-10 experiment; “B” is SPS-11, and so on with “Z” representing the SPS-35 experiment. The third and fourth positions indicate project id (00) or SPS experiment designated section id (01 to 58)/ supplemental section id (59-99).

GPS sections SHRP_ID:

Construction Number (CONSTRUCTION_NO) is an event number used to relate changes in pavement structure with other time dependent data elements. CN= 1 when a test section is initially accepted into LTPP and is incremented with each change in the layer structure.

For each maintenance and rehabilitation treatment applied to a test section after the start of monitoring under the LTPP program, the CONSTRUCTION_NO (CN) is incremented in the EXPERIMENT_SECTION table. The codes in the CN_CHANGE_REASON field indicate what type of activity was performed to cause the change in CN (For example, a CN_CHANGE_REASON of 19 represents the application of an asphalt concrete overlay). Please see MAINT_WORK codes for the complete code list of CN_CHANGE_REASON. The field CN_ASSIGN_DATE provides a date when the CN event occurred.

Under Data on the InfoPave website, go to the ‘Section Summary Reports’ and select the State/Province and section SHRP ID number that you have in mind. For example, if you select Vermont from the ‘State’ drop-down menu and 50-1002 from the ‘Section’ drop-down menu, the section overview will tell you that this test section belongs to the GPS-1 experiment, and its coordinates are (44.11961, -73.17939). You will also find that it is located in Addison County on US-7 north bound.

As all the table, field, and code information is provided along with the downloaded data, it is no longer necessary for the user to search for this data individually.

If the user is interested in getting the table, field, and codes for all tables in PPDB, it is recommended to download the LTPPTD, LTPPDD, and CODES tables that provide this information using the ‘SQL Export’ feature or using ‘SDR Export’ feature in InfoPave.

In Data Selection and Download, Pavement Structure and Construction select Original Surface construction dates. In any other data export option use the following:

For GPS sections, the INV_AGE.CONSTRUCTION_DATE and INV_AGE.TRAFFIC_OPEN_DATE fields should have the data if state agencies provided the information.

For SPS sections, the SPS_ID.DATE_COMPLETE and SPS_ID.DATE_OPEN_TRAFFIC fields should contain the data if state agencies provided the information.

No. The LTPP Pavement Performance Data Base (PPDB) has different levels of data quality (from A through E, where level E data is the highest quality that has passed all the checks). This is indicated by the field “Record Status” in each table. The Ancillary Information Management System (AIMS) data is stored based on the guidelines but do not have this quality check associated with it.

LAYER_NO is a unique sequential number assigned to pavement layers, starting with layer 1 as the deepest layer (subgrade).  

The recent LTPP data analysis project conducted backcalculation of pavement structural parameters based on all of the falling weight deflectometer (FWD) deflection data collected until 2012. These backcalculated data can be accessed through the Data Selection and Download, SQL Export, and Table Export features.

Please note that some of these data may be absent because some States or Provinces did not provide complete records of maintenance and rehabilitation histories. Any available information can be found under Maintenance and Rehabilitation (M&R) in the “Pavement Structure and Construction” class in the “Data Selection and Download” feature. In order to make sure you are looking at the complete list of tables, check the “Show Advanced Data Classification” option.

The LAB_CODE field is a four-digit character field to help users identify where the laboratory is located and who performed the test. Using the STATE_CODE definition, the first two characters represent the State in which the laboratory is located. The third character indicates what laboratory performed the test (a coded value with details in the CODES table) and the fourth character represents the sample’s test number and is sequentially numbered from 1-9, then A-Z.

The "Climate" class of the "Data Selection and Download" feature lists all the climate tables/fields that have available climatic information. In order to make sure you are looking at the complete list of climate tables, check the "Show Advanced Data Classification" option. You may also choose to narrow down your sections using "Find Sections" before selecting the data to get your desired data set.

Using the “Data Selection and Download” feature under Data, under the "Performance" class, check the “Show Advanced Data Classification” option. The Friction table will be under Surface Characteristics. If you click on “Add to Selection” option, you will be able to preview the data or you can select “Add to Data Bucket” option to download the data.

Transverse profile measurements are performed on LTPP PCC surfaced test sections and rut depths are computed from these values. One reason for transverse profile measurement on LTPP PCC test sections was to measure the effective pavement cross slope.

Laser measured transverse profiles collect over 2000 points across the width of the section at approximately every inch in the longitudinal direction. The dipstick collects data at approximately dozen points at every fifty feet in the longitudinal direction. The resulting computations are influenced by both the accuracy of the methods and the precision with which the rut values can be defined. Evaluating potential discontinuities and different trends or estimates should consider the measurement technology. The measurement technology used can be determined using the device code associated with a measurement record.

Contact LTPP Customer Support Service, ltppinfo@dot.gov to get assistance in identifying the locations needed and obtaining a custom extraction.

Axle load distributions, axle per truck values and base year AADTT and growth functions and factors for all LTPP sections can be found in Data Selection and Download as Inputs for AASHTOWare Pavement ME Design under Traffic Inputs for Pavement Analyses.