Certification Approaches for Weigh-In-Motion Systems in Law Enforcement Applications

Abstract

Every day, overweight and excessively heavy vehicles cause damage to roads, bridges, and other vehicle-based infrastructure. To protect the vital transportation infrastructure for the U.S., states have imposed weight limits for commercial and fleet transport vehicles. A common way for enforcing these weight limits is to guide trucks off the road to weigh stations where the vehicles can be weighed using static truck scales. A disadvantage of these dedicated weigh stations is that they take up a substantial amount of space (which is not always available) and time to conduct weighments, as well as cause delays to traffic flow that may impede commerce based on truck transport. A solution to these problems is the use of high-speed weigh-in-motion (WIM) systems that are installed in the road and weigh vehicles as they pass by while maintaining their speed. For jurisdictions to effectively use a WIM system for direct enforcement of weight limits, the system must be evaluated against a recognized standard to establish suitability for its intended application. The vast majority of weighing instruments used for legal metrology purposes (including law enforcement) need to comply with the requirements in NIST Handbook 44 Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. However, the NIST Handbook 44 does not (yet) cover WIM systems for direct enforcement. Although state and local jurisdictions use NIST Handbook 44 to certify legal metrological instruments, it does not exclude jurisdictions from using additional technical standards to certify certain instruments. New York City recently certified a WIM system to protect a critical section of the Brooklyn-Queens Expressway (BQE) by designating it as a pilot project while efforts were made to amend NIST Handbook 44 to include WIM systems for direct enforcement. This publication discusses the main characteristics of WIM systems and how they can be used for direct enforcement. An overview of several alternative documentary standards that can be applied for certification of WIM systems is also provided, with further explanation regarding how the New York City Department of Transportation (NYCDOT) implemented the certification of the WIM system to begin issuing citations to overweight vehicles in an effort to protect the BQE.