Vehicle emissions control now encompasses sources beyond tailpipe after treatment, because while exhaust limits remain important and internal-combustion vehicles still require combustion-emissions control, recent regulatory tightening and the adoption of electrified powertrains have increased focus on particulate emissions originating from braking, tires and road surfaces rather than engines.

The EU made the shift explicit in Regulation (EU) 2024/1257, the Euro 7 regulation. Euro 7 covers exhaust emissions and durability requirements, but it also brings brake-particle emissions and tire-abrasion emissions into the vehicle type-approval framework. That change does not turn every non-exhaust source into a single certification number, but it does make chassis, brake and tire design more relevant to emissions compliance.

Electrification introduces additional complexity, given that battery-electric vehicles produce no tailpipe emissions during operation and hybrid or electric drivetrains can employ regenerative braking to reduce reliance on friction-based braking. However, these advantages do not eliminate non-exhaust particle emissions, as all road vehicles continue to use tires, apply friction brakes under specific conditions, traverse pavement and disturb deposited road material.

Non-exhaust PM has separate sources

Non-exhaust particulate matter (PM) covers several mechanisms. Brake-particle emissions come from friction materials and rotating brake surfaces during pad-disc, shoe-drum or related contact; tire abrasion comes from tire-road contact and depends on load, compound, tread design, alignment, pavement texture and driving style; road-wear particles come from the pavement or road surface. Resuspended road dust is material already on the road that traffic returns to the air through tire action, vehicle wake and local turbulence.

These distinctions constrain the claims that can be made regarding braking technologies. A braking controller can influence friction-brake application, brake-torque distribution and the integration of regenerative braking; however, it cannot directly affect tire-compound wear, pavement abrasion, or the resuspension of dust already present on the roadway. Inventory methods also distinguish between primary tire, brake and road-wear particles and resuspended material, although real-world samples often contain mixtures from multiple sources.

Institutional trend data indicate increased scrutiny of these categories, with the European Environment Agency reporting that overall particulate matter emissions in the EU-27 decreased by 53% from 1990 to 2023, while non-exhaust road-transport emissions from tires, brakes and road abrasion increased by 63.1%. This trend does not demonstrate that any specific brake technology reduces particle emissions, but it clarifies why regulators and engineers now address non-exhaust particulate matter as a distinct technical and compliance issue.

Euro 7 and UNECE change the measurement context

Euro 7 covers M- and N-category motor vehicles and also includes O3 and O4 trailer categories, with separate provisions for tires. The main Euro 7 application dates begin with new M1 and N1 vehicle types on November 29, 2026, all new M1 and N1 vehicles on November 29, 2027, and the new M2, M3, N2, N3, O3 and O4 types will be introduced on May 29, 2028, with all new vehicles in those categories introduced on May 29, 2029. Small-volume manufacturers receive later dates of July 1, 2030, for M1 and N1 vehicles, and July 1, 2031, for M2, M3, N2 and N3 vehicles.

The light-duty brake-particle limits are defined as PM10 mass limits, which vary by powertrain type and vehicle class. For M1 and N1 vehicles, excluding N1 Class III, the limit is 3 mg/km for pure electric vehicles and 7 mg/km for plug-in hybrids, non-plug-in hybrids, fuel-cell vehicles and internal-combustion vehicles. For N1 Class III vehicles, the respective limits are 5 mg/km and 11 mg/km. These differentiated limits are regulatory requirements and do not indicate that electric vehicles are free from friction-brake emissions.

Tire abrasion is subject to a distinct implementation timeline. Euro 7 introduces tire-abrasion requirements, with new tire-type compliance dates commencing on July 1, 2028, for C1 tires, April 1, 2030, for C2 tires, and April 1, 2032, for C3 tires. Full compliance remains contingent on staged implementation and on ongoing developments within United Nations Economic Commission for Europe (UNECE) and the EU. Current evidence supports a limited conclusion: tire abrasion is being incorporated into the regulatory framework, but the specific limits, measurement methods, and class coverage are not yet fully established.

UNECE initiatives introduce an additional layer of standards: UN Regulation No. 179 addresses laboratory measurement of brake emissions for light-duty vehicles, although it is distinct from Euro 7, which constitutes EU law, recent EU implementation efforts have sought to align Euro 7 light-duty brake testing with UN R179, moving away from previous reliance on UN Global Technical Regulation No. 24. The European Commission’s delegated acts connect laboratory brake-emission measurement to M1 and N1 vehicles and specify PM10, PM2.5 and particle-number measurement protocols. The UN treaty notification outlines the procedural steps under the 1958 Agreement, including a six-month objection period prior to adoption and entry into force, which is significant because adoption, notification, EU alignment and application by contracting parties represent related but distinct legal processes.

Regeneration changes brake use, not all wear mechanisms

Regenerative braking changes the duty cycle of the friction brake. In an electric vehicle or hybrid, the traction motor can act as a generator during deceleration, converting part of the vehicle’s kinetic energy into electrical energy rather than dissipating it entirely as heat at the friction surfaces, which can reduce pad and rotor wear in routine driving.

But it does not remove the vehicle's friction braking. Friction brakes remain necessary for emergency stopping, stability-control intervention, parking, low-speed operation, fallback operation and conditions where battery state, temperature or motor limits restrict regenerative braking, and tire-road contact also continues during every mile of travel, so tire abrasion and road-wear particles remain outside the direct reach of brake blending.

The OECD estimated that electric vehicles emit 5% to 19% less non-exhaust PM10 than internal-combustion vehicles across various vehicle classes. Additionally, PM2.5 outcomes are influenced by vehicle mass, with lighter electric vehicles estimated to emit less and heavier electric vehicles estimated to emit more than comparable internal-combustion vehicles. The engineering implication is that electric vehicles are not categorically cleaner or dirtier with respect to all non-exhaust particulate matter; particle size, vehicle mass and source category all influence the outcome.

Brake-by-wire is a control tool, not a standalone solution

A brake-by-wire system separates the driver’s braking request from a direct mechanical command path and transmits it electronically. This architecture can support more precise coordination between regenerative braking and friction braking, because software can allocate deceleration demand across electric machines and wheel brakes while preserving pedal response and stability functions.

But brake-by-wire does not refer to a single actuator type. Electrohydraulic brake-by-wire decouples pedal input and pressure generation while still using hydraulic pressure at the wheel brakes. Electromechanical braking uses electric actuation to generate clamping force and can form a dry architecture without service-brake hydraulic circuits. Conventional friction braking remains the pad-disc or shoe-drum process, which generates braking torque and wear particles when surfaces contact under load.

Production evidence illustrates why this architecture is now relevant to the discussion of non-exhaust emissions, but its evaluation requires clear boundaries. Brembo reports that Sensify entered large-scale series production on May 4, 2026, for an undisclosed leading global vehicle manufacturer. The system is described as a fluid-free architecture featuring wheel-level distributed intelligence, no hydraulic circuits and no centralized actuation, which are claims that establish the production relevance of software-controlled and electromechanical braking systems, but they do not independently verify real-world reductions in brake particle emissions. Similar caution should be applied to statements from other suppliers regarding brake-by-wire, hybrid or dry-braking architectures unless supported by independent brake-emission testing or compliance data.

It can safely be concluded that brake-by-wire systems can facilitate management of friction brake application, braking torque distribution and the integration of regenerative and wheel braking, and this control capability can support compliance efforts under brake-particle measurement regimes. However, brake-by-wire cannot substitute for low-wear friction materials, optimized rotor and pad design, standardized brake-emission testing, tire development, vehicle mass management, road-surface analysis or rigorous calibration. While non-exhaust particulate matter is now sufficiently measurable to regulate, it continues to present a complex systems challenge.