The Evolution of Automotive Brake Emission: Part 1 of 3

Updated: Jun 14

Written by: Carlos Agudelo

Image of a city with smog
Automotive Brake Couplings Emission also contribute to Air Pollution

Image Credit: Tomskyhaha, CC BY-SA 4.0, via Wikimedia Commons

Five things the industry has done already to address brake emissions

Image of a disc brake

Brakes wear, depending on their specific gravity, can become either airborne or deposited on the road.. Irrespective of the amount, the fate, and the health effects of brake emissions, the industry and regulatory entities worldwide have taken proactive and preventive measures to lessen brake emissions. These are ten areas or activities where the industry, government agencies, and research institutes have developed active measures or projects on particulate matter emitted during braking. Some activities have already increased the scientific and engineering understanding of such a complex aspect of the transportation industry.

"All happy families are alike, but every unhappy family is unhappy in its own way." Leo Tolstoy, Anna Karenina, 1878

All low-emitting brakes are alike (like low operating temperatures, well-balanced brake distribution, low wear friction couples, safe driving habits, strict quality controls in manufacturing, low brake drag, and stable coefficient of friction). Different reasons—sometimes independent and sometimes colluding, can generate brake emissions at much higher rates (such as unbalanced brake force distribution, poor brake cooling, non-technical brake jobs, vehicles with out-of-service conditions, aggressive driving or vehicle overloading, partial formulation designs, lack of repeatable and stable manufacturing and assembly, or unintended effects from failures from other components). These are some of the nuances which keep environmental and health professionals, friction designers, and applications engineers up at night.

The last ten years have seen a surge in efforts from multiple stakeholders that, when put together, provide a clearer image of the path the industry is following to reduce harmful environmental and health effects from everyday driving. Something which was not as obvious ten years ago, when brake dust was mainly a cosmetic concern. The list is not exhaustive, and there are many areas where other sectors like rail transport, or individual companies like those developing on-vehicle capturing devices, testing systems, and vendors of measurement instruments, are making significant progress.

1. Develop the WLTP-Brake cycle within the European Commission

As of 2019, the European Commission published the Worldwide harmonized Light vehicle Test Procedure (GRPE 81-12) to represent the average driving profile in a 4.5-hour driving cycle (6-8 total run time) using data from over 750 000 km of data collected in different regions. The dynamometer cycle includes ten trips, 303 braking events, and 192 km of driving distance with city, suburban, and highway driving. The development took multiple iterations of vehicle testing at the Lommel proving ground, and the brake cooling method used input from in-vehicle testing in the United States by California Air Resources Board, CARB. This work's inception was in 2014 when the European Commission established the Informal Working Group. The IWG was given the charter to work towards the" […] development of a set of recommended measurement techniques and sampling procedures, the investigation of typical driving patterns, the compilation and monitoring of on-going research projects, as well as the networking and exchange of information with experts in the field of non-exhaust traffic related particle emissions […]". The current work of the IWG includes four task forces (1) driving cycle, (2) laboratory method, (3) interlaboratory studies, and (4) regenerative braking systems.

2. California updates brake and tire emissions models and expands the scientific knowledge

The California Air Resources Board and the California Department of Transportation embarked on several projects to update the knowledge base, update the emission factors models (EMFAC2021) for particulate matter, and support environmental justice initiatives. The research efforts include: Measure brake wear emissions under controlled conditions and different driving conditions (17RD016); Brake Wear in Particulate Matter Emission Modeling (CalTrans Project No. 65A0703); Real-World Tire and Brake Wear Emissions (18RD017); In-house brake wear measurements; and Collaboration with the European Joint Research Centre.

3. Japan releases first laboratory method to measure brake emissions

Based on pioneering work from the Japanese Automotive Research Institute, the Society of Automotive Engineers of Japan (JSAE) published the JASO C470 Passenger car - Measurement method for brake wear particle emissions. The laboratory method provides specific requirements and descriptions of crucial elements such as brake inertia, system layout, minimum set of instruments, climatic controls, background emissions, and the actual driving pattern. After the burnish (bedding) section, the test includes 30 cycles combining urban road and highway modes with moderate speeds and decelerations, derived from the experience with other driving schedules. JARI has multiple publications and contributions to PMP, SAE, EuroBrake, and environmental journals. A simple search for "Hagino brake emissions" on Google Scholar will open a trove of knowledge.

4. Multiple funding initiatives from different entities

Image shows sand compared to human hair

Tiny (brake) particles create enormous challenges.

One of them is the fate of the debris emitted during braking (or during acceleration or cruising where there is brake drag) and the mix between brake, tire, road, and other errand sources (from industrial activities, construction households, and natural like marine, wildfires, and dust). Determining the amount, composition, toxicology, mixing, and dependency on time, weather, and traffic has been a dominant aspect of research and field measurements funded by various entities. The initiatives from CARB, U.S. EPA, HEI, the European Parliament, and the Horizon Europe from the European Commission's funding programme are worth mentioning. The projects range from advanced technologies and on-road measurements to air pollution effects to retrofit devices to capture brake emissions at the source. Other countries and industry consortia fund multiple initiatives. Some projects attempt to improve tools and data to understand the different transport mechanisms in the vehicle and onto the road and the atmosphere, which ultimately can become respirable to humans.

Images shows a drawing of wheel technology

5. Electrification

Electric powertrains have become one of the leading technologies to reduce the need to rely on the service (friction-based) brakes to slow down the vehicle during everyday driving. The pulse rate of electrification (sales volumes, new models, and charging network) is accelerating, as demonstrated by the three graphs below. The entire Global EV Outlook 2022 - Securing supplies for an electric future report and more from the International Energy Agency is available here. The three graphs below depict the recent developments in vehicle sales, expansion of electrified commercial vehicles, and deployment of charging stations worldwide.

From the same iea report:

[…] China accounted for nearly 90% of electric truck registrations in 2021, down from nearly 100% in 2017. Sales in the United States and Europe have begun to rise rapidly in the past few years,[…]
Graph titled Electric car sales spiked in emerging markets in 2021

Graphs showing Electric bus and truck models expanding

Charging infrastructure is expanding significantly - a graph

It has become evident that the industry is coalescing around the common goal of making transportation systems cleaner and lessening the burden on the environment and human health. It will take the entire industry to transform itself—more on this in future blogs.

In Part 2, I will discuss how the next decade will likely shape the future of Automotive Brake Coupling Emission.

Carlos Agudelo is Director of Applications Engineering for LINK Group, developing new features and systems based on data and experimentation, emphasizing non-exhaust brake emissions and Hardware-in-the-Loop. Carlos obtained his bachelor’s degree in Production Engineering from EAFIT University-Colombia (in association with Aachen University and Ruhr University Bochum) and a Six Sigma Black Belt certification. He is Chairman of the SAE Brake Dynamometer and the Vehicle Dynamics Standards Committees, Vice-Chairman of the SAE Brake Lining Standards Committee, and the Truck & Bus Hydraulic Brake Committee. He is active on SAE, ISO, and PMP Committees and task forces. Carlos is a member of and an instructor in Brake Academy.

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