Railroad Weight Standards FAQs

Master scales are calibrated and accurate railroad track balances (i.e., scales) used exclusively to calibrate railroad test weight cars (up to 110,000 pounds ), which in turn are used to test routine railroad track scales.

The USDA Federal Grain Inspection Service (FGIS) maintains the Master Scale Depot facility in Chicago and calibrates all master scales in the U.S. annually.  Seven master scales are owned by individual Class I railroads, two master scales are State-owned (Oregon and Minnesota), and one remains with the USDA FGIS. 

The USDA Master Scale Depot is the primary master scale in the U.S. for the scope of railroad test cars and 10,000 lb test car weights, and therefore can calibrate a railroad master scale. Currently, the USDA Master Scale is used to calibrate and certify multiple test weight cars used in the field.

Learn more about the USDA FGIS Master Scale Depot here.

The Master Scale maintained by the USDA FGIS Master Scale Depot is one of the recognized metrology laboratories in the U.S. state metrology laboratory system, and has the following laboratory scope:

• Mass Echelon III
  • 10 000 lb
  • 1 000 lb
  • 50 lb
  • 25 lb
  • Railroad Test Cars 110 000 lb to 80 000 lb

The scope (or capabilities) of the state metrology laboratories includes USDA as one of two laboratories that include Railroad Test Cars on their scope. USDA is one of two laboratories with a unique mass scope at the large nominal of 10,000 lb. The USDA laboratory provides calibration services for railroad master scales, railroad track scales, railroad test cars, and 10,000 lb test car weight with a 10,000 lb test car weight cart. This is directly attributable to the USDA laboratory having sufficient standards (two 10,000 lb calibrated standards), a suitable and sufficient balance (i.e., Master Scale), metrological traceability with measurement assurance, and a competent and approved metrologist to operate such a laboratory.

• Complete list of the scope (or capabilities) of the state metrology laboratories
• Certificate of Metrological Traceability for the USDA FGIS MSD

Metrological traceability requires the establishment of an unbroken chain of calibrations to specified reference standards: typically, national or international standards, in particular realizations of the measurement units of the International System of Units (SI). Metrological traceability (i.e., SI traceability) is the key to maintaining confidence in the reference standards for U.S. industry calibration services and ultimately ensuring marketplace equity in U.S. trade and commerce.

The USDA Master Scale traceability is illustrated below for three scenarios (left-to-right): (left) railroad test car, (middle) railroad Master Scale, and (right) railroad track scale. The outlined boxes indicate where the customer product is calibrated.

Credit: NIST OWM

The Certificate of Metrological Traceability issued by NIST OWM to the USDA Master Scale Depot assures the SI traceability of its calibration measurement results provided to its customers. The Certificate of Metrological Traceability recognizes that the laboratory has achieved traceability to the SI of measurement results. This has been obtained through an official demonstration of evidence of metrological traceability to NIST Handbook 143 requirements and through an official recognition process by the OWM Laboratory Metrology Program.

To promote SI traceability and encourage technical and professional competence among participating individual state-level laboratories, the OWM Laboratory Metrology Program evaluates and provides Laboratory Recognition to these laboratories to NIST Handbook 143, which consists of additional requirements to ISO/IEC 17025. Upon the annual evaluation of a participating laboratory’s ability to deliver reliable calibration services in the areas of its scope (principally mass, volume, length, and temperature), a Certificate of Metrological Traceability is issued and accepted as reciprocity by other state-level legal metrology programs.

The current recognition status and certificate for each participating state metrology laboratory are provided here.

The U.S. State legal metrology laboratories, together with the USDA Master Scale Depot, are the custodians of state-level measurement standards. Furthermore, the model weights and measures laws in NIST Handbook 130 often require state weights and measures programs to ensure metrological traceability to the International System of Units (SI). The model weights and measures laws also indicate that calibration laboratory recognition or accreditation provides demonstrated evidence of metrological traceability.

Yes, with some limitations. Commercial railroad track scales used for commercial transactions are regulated by state and local weights and measures agencies. Most states rely on third-party registered service agencies, scale service companies, or the railroads to conduct the testing portion of the inspection. This is a consequence of the fact that suitable state-owned equipment is not readily available for such large-scale capacity scales.

Witness Testing may be conducted to ensure that the test weights (e.g., railroad test car, railroad track scale test weight, test car weight cart) all have a valid calibration certificate. A valid calibration certificate is the document that clearly demonstrates the chain of custody for traceability to the SI. The state laws in 45 states currently follow or adopt the model law in NIST Handbook 130 for Registration of Service Agencies.

For more details, see Section D, "Uniform Regulation for the Voluntary Registration of Servicepersons and Service Agencies for Commercial Weighing and Measuring Devices" model law in NIST Handbook 130, Uniformity of Laws and Regulations.

The calibration certificates issued by a legal metrology calibration laboratory that closes after the certificate is issued are valid for the period listed on the certificate. Any expiration date listed on the certificate will remain valid. If no expiration date is listed on the certificate, then the certificate remains viable.

Note: there is recommended guidance from NIST OWM on periodic recalibration of mass standards, which includes test weights and test cars. The basic guidance is established at annual recalibration for calibrated standards that are known to have wear and tear as they are manufactured of soft metal (cast iron), used in an outdoor environment, have moving parts, and/or known to contact other surfaces (scale surface, other weights, material handling equipment).

Please see NISTIR 6969 GMP 11 for further information about the calibration cycle of laboratory standards (kept in a controlled environment). For mass field standards, please see NIST Handbook 105-1 section 6.4 Initial and Periodic Evaluation and NIST Handbook 105-8 section 6.3 Periodic Calibration cycle weight carts.

The longer-term impact will reduce the availability of SI traceable calibration certificates for a specific scope (e.g., mass) in a regional area within the U.S. This is anticipated to impact the ability to ensure SI traceability downstream to consumers who may be reliant on calibration and other measurement services. The direct impact across customers and through the U.S. economic system may be difficult to assess immediately; however, each regulatory jurisdiction should consider the market impact based on the laboratory's unique capabilities and position.

The original Master Scale Depot was built in 1928 by the National Bureau of Standards or NBS (currently NIST). The Master Scale Depot was established to calibrate master scales and railroad owned test weight cars. In 1980, the NBS transferred the responsibility to maintain the programs, equipment, and the facility, which at the time included two 100,000-pound test car units to the USDA Federal Grain Inspection Service (FGIS).