The purpose of an inspection and maintenance (I/M) program is to identify high-emitting vehicles and mitigate their impact on air quality and climate. I/M programs require vehicle owners to regularly subject their vehicles to a certified emissions test. Vehicles that fail the test, due to either emissions that exceed the regulatory threshold or to emissions control component malfunctions, are required to undergo repairs. High emitters typically make up a small percentage of a vehicle fleet, but are responsible for an inordinately large amount of total emissions.
This white paper expands on the general ideas for I/M programs first outlined by a previous ICCT report on in-use emission controls for heavy-duty vehicles (HDVs) and is also a continuation of the evaluation of international best practices for in-use programs that started with the publication of the HDV replacement report. This new paper reviews the best practices for I/M programs targeting heavy-duty vehicles, evaluates existing HDV I/M testing methods and protocols and their limitations, examines new and emerging techniques for HDV I/M testing, evaluates a range of HDV I/M programs across the globe, and makes recommendations about how to improve HDV I/M programs in the future.
With respect to I/M testing methods, the core component of these programs, we note that current I/M programs for HDVs rely on two main testing methods: the free acceleration smoke (FAS) test and the lug down smoke test. These two tests were developed for legacy diesel technology and are inadequate for particulate matter measurement on newer vehicles. These tests were also not designed to measure NOx emissions.
There are a number of measurement technologies and testing methods that could be utilized to improve I/M programs. Improving the measurement of particles will likely involve a shift from conventional opacimeter to advanced technologies that can read a wider range of particle sizes and concentrations, such as laser-light-scattering photometry (LLSP). Measuring NOx and nitrogen dioxide (NO2) under I/M programs could be done using non-dispersive ultraviolet absorption spectroscopy (NDUV). Alternative testing methods that can complement or replace traditional I/M methods include the use of on-board diagnostics (OBD), remote sensing, and the On-road Heavy-duty Vehicle Emissions Monitoring System (OHMS).
While only a handful of countries and sub-national governments have implemented I/M programs for controlling high-emitting HDVs, we recommend that all countries adopt some form of an I/M program for HDVs, based on their specific situation and following the best practices outlined in this paper.