Publication Number: FHWA-HRT-08-065
Date: November 2008
Long-Term Pavement Performance Compliance With Department of Transportation Information Dissemination Quality Guidelines
CHAPTER 2. COLLECTION OF DATA
The DOT IDQG regarding the collection of data are generic to encompass a wide range of data collection methods. LTPP data collection methodology is best characterized as a mix of one-time surveys, periodic collection of condition data, continuous reporting of climate and traffic loading, and compilation of data collected by others.
The LTPP data collection operations comply and, in some cases, surpass the DOT's IDQG. The LTPP data collection operations include an array of techniques including data collection forms, electronic measurement systems, automated data acquisition, and use of data collected by third parties. The one data collection approach not used by LTPP is a statistical response survey. Some of the LTPP activities noted under data collection operations should be considered for addition to the DOT guidelines.
Data Collection Operations
With the vast array of data collection methods employed by the LTPP program, the following operational procedures had to be developed:
- All data recorded on paper forms included written instructions on all requested pieces of information.
- When possible, all pertinent information needed to complete a paper form were included on the form. For example, when codes were used to represent a response, the codes were printed on the form.
- All forms were numbered and dated for document control.
- Revisions to forms were issued in a formal directive documenting changes.
- A response was requested for all information items contained on the form. A "NA" was requested when a piece of information was not available or was not appropriate to confirm that the requested data item was considered or ignored.
- Data collected by instrumentation require a calibration process or a check on the state of calibration of the instrument used.
- For the vast array of LTPP operated measurement instrumentation, requirements for instrument calibration or checks on the state of calibration were specified.
- Where required, calibration procedures were developed by the program.
- Where possible, calibration procedures were specified that could be traced back to the National Institute of Standards and Technology.
- Adjustments to equipment calibration factors were documented and stored in the database.
- When adjustments to measurement equipment calibration factors were not possible, guidelines were developed to check equipment calibration and to return it to the manufacturer for recalibration or discard and purchase new equipment. The guidelines include rules on disposition of data collected using equipment found to be out of calibration after measurement.
- Field checks for reasonableness of data from electronic measurement equipment were developed. Many of these checks involved computer programs that plotted a data time history that permitted an assessment of operational condition. Guidelines were published to aid technicians to recognize faulty equipment. This allowed trouble shooting and repair activities to be conducted in the field whenever possible.
- Before using equipment for measurement of critical test section characteristics, side-by-side equipment measurement studies were conducted.
- Electronic data obtained from third parties were evaluated and subjected to automated QC checks before entry into the LTPP database.
- Errors were found from checks of climate data obtained from the NCDC. The errors where the supplied data indicated that the average daily air temperature was not between the low and high temperature for the day was flagged and not used in calculations.
- Traffic volume, classification, and weight data supplied by participating highway agencies were preprocessed through software developed by the LTPP program to detect a variety of known errors. Data error reports were then sent back to the agency for review and comment.
- In order to better interface with participating highway agencies, North America was divided up into four "data collection" regions based on the number of agencies in each region. Regional data collection support centers were established in each region to coordinate data collection activities with highway agencies. The regional centers are responsible for collection, review, and processing of critical data and review and processing of all data on test sections located in their region.
Missing Data Avoidance
Missing data avoidance is a significant issue for a program like LTPP that relies on voluntary participation by highway agencies for supply of important data elements. The program also relies on notification from highway agencies prior to the application of maintenance and rehabilitation treatments so that pavement condition measurements can be made. Some of the steps employed by the LTPP program to reduce missing data include the following:
- The regional data collection contractors have established data tracking systems to track the status of data collection and processing functions for the test sections in their territory.
- The paper data collection forms sent to highway agencies used a positive feedback response methodology where data items not applicable were marked as such. This method was used to avoid confusion over items on data forms left blank.
- Group meetings were held with participating highway agencies on a regional basis where data needs and requirements were discussed. Data packets and status reports on missing data were distributed to agency representatives at these meetings.
- Visits to each agency were performed to follow up on data needs and discuss the status of missing data.
- In some cases, it was necessary to send contractor staff to the highway agencies' offices in order to obtain the needed data directly from agencies' files.
- An internal assessment of the program was performed in 1996. One of the results of this assessment was the development of a formal program to identify missing critical data and formulate a plan to obtain the needed data. Visits with all participating highway agencies were held. A signed agreement was obtained from each agency to document what data would and would not be supplied by the agency.
- From this assessment, a pooled fund study was set up with participating highway agencies to obtain missing traffic monitoring data on high-priority test sections. The benefits of the pooled fund study approach to this highly technical area of data collection were the opportunity to provide centralized expert resources and to lessen the impact of manpower resources at the agency to provide this data.
- In another instance, program funds were reallocated to obtain missing materials data, which were the responsibility of participating highway agencies, on a subset of high-priority test sections. In this exercise, the new data collection effort was based on an assessment of both missing and questionable data.
- While some of these efforts have been documented in various methods, due to the engineering research nature of the LTPP program, it is LTPP management's position that a data user would not benefit from information on the procedures used to avoid missing data. Therefore, these procedures are not disseminated with the data.