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Publication Number: FHWA-RD-03-088
Date: November 2003

Introduction to The LTPP Information Management System (IMS)

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The Traffic (TRF) module contains agency estimates, computed annual estimates of traffic volumes and loads, and supporting measurement information on the traffic characteristics in the LTPP test section lane. In the development of the LTPP program, participating highway agencies have agreed to provide traffic monitoring measurements for test sections in their jurisdiction. Traffic volume and loading estimates for time periods prior to the start of LTPP traffic monitoring in 1990 are referred to as "Historical" data, while the information derived from the installed monitoring equipment (or from estimates for those test sections that had no monitoring equipment until some time after 1990) is known within the program as "Monitoring" data. Table names within the TRF module reflect the source of the data stored within them.

The LTPP traffic data collection plan has been developed to balance the needs of the research program and the constraints of existing technology and finite highway agency resources. The plan recognizes several major principles:

Traffic data collection for LTPP sections is a State/Provincial responsibility. Data collection plans from each agency have integrated the LTPP requirements and individual State/Provincial practices. This has resulted in site-to-site variability in the amount and type of data being collected for the LTPP program that greatly exceeds the variability found in the other data modules.

12.1 IMPORTANT FIELDS

Common fields unique to the TRF tables that can be used to link related data in associated tables to each other include VEHICLE_CLASS, AXLE_GROUP, CLASS_COUNT_BEGIN_DATE, and WIM_AVC_CALIB_DATE.

VEHICLE_CLASS refers to the FHWA 13-bin vehicle classification system (table 4). (Note that athough the classification system is named 13-bin for historical reasons, it has 15 categories.) This field can be used to link the number of vehicles weighed within each class (from the TRF_HIST_WEIGHT_DATA table) to the distribution of axle group weights for these classes (from the TRF_HIST_WEIGHT_AXLES table). This field is also used within TRF_HIST_CLASS_DATA to indicate the number of vehicles within each category that were counted during classification surveys. The similar VEHICLE_CLASS field within TRF_MONITOR_AXLE_DISTRIB can be used to link data to the TRF_HIST tables, but only for the truck categories (classes 4 through 14) since motorcycles, automobiles, and light trucks are not present in weigh-in-motion (WIM) monitoring data.

Table 4. FHWA 13-bin vehicle classification system.

Vehicle Class

Description

1

Motorcycles

2

Passenger cars

3

Other 2-axle, 4-tire single-unit vehicles

4

Buses

5

2-axle, 6-tire single-unit trucks

6

3-axle single-unit trucks

7

4- or more axle single-unit trucks

8

4- or less axle single-trailer trucks

9

5-axle single-trailer trucks

10

6- or more axle single-trailer trucks

11

5- or less axle multi-trailer trucks

12

6-axle multi-trailer trucks

13

7- or more axle multi-trailer trucks

14

Unclassifiable

15

Partial vehicles, including offscale or lane-changing vehicles

AXLE_GROUP is a variable that defines the type of axle or axle group (single, tandem, triple, or quad). The variable is used within the TRF_HIST_WEIGHT_AXLES and TRF_MONITOR_AXLE_DISTRIB tables. Note that steering axle groups are not recorded separately from other single axles in this table.

CLASS_COUNT_BEGIN_DATE may be used to relate information on a specific historical traffic classification count that is stored within the TRF_HIST_CLASS_MASTER table with the actual count data that is stored in TRF_HIST_CLASS_MASTER.

WIM_AVC_CALIB_DATE must be used when relating the specific calibration factors found within TRF_CALIBRATION_AVC and TRF_CALIBRATION_WIM to the list of installed traffic monitoring equipment found within TRF_EQUIPMENT_MASTER.

12.2 TRF TABLES

TRF_BASIC_INFO: This table contains basic information about the location of the section and the roadway on which it is located.

TRF_CALIBRATION_AVC: This table contains information on the calibration of automated vehicle classification (AVC) equipment installed at a test section.

TRF_CALIBRATION_WIM: This table contains information on the calibration of weigh-in-motion (WIM) equipment installed at a test section.

TRF_EQUIPMENT_MASTER: This table contains information about equipment (both AVC and WIM) in place during a calibration event.

TRF_EXTRACTOR: This table is used for internal database functions.

TRF_HIST_CLASS_DATA: This table contains the results of vehicle classification counts that were taken by the State/Provincial agency prior to the start of LTPP traffic monitoring and were used to estimate vehicle distributions at the site. These counts were not necessarily taken at the site itself.

TRF_HIST_CLASS_MASTER: This table contains the specifics of the classification counts that furnished data for TRF_HIST_CLASS_DATA. The CLASS_MASTER table also contains the total volumes recorded during each count.

TRF_HIST_EST_ESAL: This table contains estimates of 80-kN (18-kip) equivalent single-axle loads (ESALs) at the section for each year from construction (or 1965, whichever is later) to its inclusion in the LTPP program.

TRF_HIST_VOLUME_COUNT: This table contains the results of vehicle volume counts that were taken by the State/Provincial agency prior to the start of LTPP traffic monitoring and were used to estimate traffic volumes at the site. These counts were not necessarily taken at the site itself.

TRF_HIST_WEIGHT_AXLES: This table contains the results of truck weighing sessions that were conducted by the State/Provincial agency prior to the start of LTPP traffic monitoring and were used to estimate traffic loading at the site. These counts were not necessarily taken at the site itself.

TRF_HIST_WEIGHT_DATA: This table contains the number of vehicles weighed during the sessions in which TRF_HIST_WEIGHT_AXLES information was extracted.

TRF_HIST_WEIGHT_MASTER: This table contains all general information on the roadway and the equipment used for historical truck weighing sessions.

TRF_LIBRARIAN_INDEX: This table is used for internal database functions.

TRF_MONITOR_AADT: This table contains information about the traffic characteristics of the LTPP section or project. This table contains estimates of total and truck annual average daily traffic (AADT)for the road and for the LTPP lane. This table also summarizes the amount of monitoring data used to create these estimates. Since the LTPP program requires only monitoring of a single lane in which the test section(s) is located, this table will be removed from the database in the future.

TRF_MONITOR_AXLE_DISTRIB: This table contains the number of axles measured in each weight range for each axle group (single, tandem, triple, and quad). This information is obtained from weigh-in-motion (WIM equipment installed at or near the test section. Note that steering axle weight distributions are not recorded separately from other single axles in this table.

TRF_MONITOR_BASIC_INFO: This table contains summary information concerning the extent of data collection and site characteristics on a yearly basis.

TRF_MONITOR_LTPP_LN: This table contains information on the amount of data collected on a vehicle class basis and the estimated annual volumes of trucks and axles associated with that data for the LTPP lane only.

TRF_MON_EST_ESAL: This table contains an annual estimate of the number of 80-kN (18-kip) ESALs in the study lane and estimates of truck and total vehicle volumes. The data within this table are for the period from 1990 until the test section was instrumented with monitoring equipment. The estimates are supplied by the highway agency.

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
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