American Society for Testing Materials

ASTM has established a Standard Specification for Highway Weigh-in-motion Systems E1318 which is used by most WIM users around the world as a guideline. The latest revision was published in February 2009.

The Standard has about 20 pages of specifications covering:

  • definitions
  • four different types of WIM systems (Type I, II, III and IV) and their main application
  • site specifications
  • testing and calibration requirements
  • data recording
  • ESALs calculations.

The WIM Classifications defined in the Standard are:

  • Type I – high accuracy data collection systems (typically bending plate scale type WIM)
  • Type II – lower cost data collection systems (typically piezoelectric scale type WIM)
  • Type III – systems for use in a sorting application at weigh station entrance ramps (bending plate or deep pit load cell type WIM)
  • Type IV – low-speed WIM. It is designed for use at weight enforcement stations to detect weight-limit or load-limit violations. Speeds from 2 to 10 mph (3 to 16 km/h), inclusive, are accommodated.

Function performance requirements can be found in the table below. Most Australian and New Zealand WIM system operations conform to the ASTM standard specifications.

Table: Functional performance requirements for WIM systems
Function Tolerance for 95% compliance *
Type I Type II Type III Type IV
Value ≥ lb (kg)** ±lb (kg)
Wheel load ±25%   ±20% 5 000 (2 300) 300 (100)
Axle load ±20% ±30% ±150% 12 000 (5 400) 500 (200)
Axle-group load ±15% ±20% ±10% 25 000 (11 300) 1 200 (500)
Gross vehicle weight ±10% ±15% ±6% 60 000 (27 200) 2 500 (1 100)
Speed ±1 mph (2 km/h)
Axle-spacing and wheelbase ±0.5 ft (0.15 m)

* 95% of the respective data items produced by the WIM system must be within the tolerance.

** Lower values are not usually a concern in enforcement.

Source: ASTM 2009.

COST 323

COST 323 is one of the actions supported by the COST Transport part of the European Commission's Transport Directorate, DG VII.

Following a proposal of the FEHRL group, COST 323 was initiated in 1992. Since 1993 it has been run by the Management Committee, a group of scientific and technical experts, to promote the development and implementation of weigh-in-motion techniques and their applications, and to facilitate an exchange of experiences between different European countries.

COST 323 does not constitute an official standard but provides technical specifications for WIM users and manufacturers and a reference upon which standardisation committees can draw.

The main objectives of the COST 323 action are:

  • complete an inventory of WIM requirements in Europe
  • collect and evaluate existing WIM information
  • undertake preliminary work on the development of a European technical specification on WIM
  • agree mechanisms and protocols for a pan-European database of WIM sites and data
  • collect and disseminate scientific and technical information
  • exchange experiences and conclusions from other international projects.

COST 323 defines WIM systems by classes based on their level of accuracy. These classes are defined as follows, where the numbers in brackets indicate the confidence interval width:

  • Class A(5): Legal purposes such as enforcement of legal weight limits.
  • Class B+(7): Enforcement of legal weight limits in particular cases, if the Class A requirements may not be satisfied, and with a special agreement of the legal authorities; efficient pre-selection of overloaded axles or vehicles.
  • Class B(10): Accurate knowledge of weights by axle groups, and gross weights, for:
    • infrastructure (pavement and bridge) design, maintenance or evaluation, such as aggressiveness evaluation, fatigue damage and lifetime calculations
    • pre-selection of overloaded axles or vehicles
    • vehicle identification based on the loads.
  • Class C(15) or D+(20): Detailed statistical studies, determination of load histograms with class width of one or two tonnes, and accurate classification of vehicles based on the loads; infrastructure studies and fatigue assessments.
  • Class D(25): Weight indications required for statistical purposes, economical and technical studies, standard classification of vehicles according to wide weight classes (e.g. by 5 t).

Additional Classes E(30), E(35), etc. are defined for WIM systems which do not meet the Class D(25) requirements. These classes may be useful to give indications about the traffic composition and the load distribution and frequency.

Further reading

Standard specification for highway weigh-in-motion (WIM) systems with user requirements and test methods, E1318-09, American Society for Testing Materials, West Conshohocken, PA, USA

Forum of European National Highway Research Laboratories, 1999, COST 323: Weigh-in-motion of road vehicles, Final Report, Appendix 1 European WIM Specification, Laboratoire Central des Ponts et Chaussees (LCPC), Paris, France

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