NHTSA has given the industry another 30 days to comment on its proposal to rewrite the federal light vehicle brake standard for driverless vehicles, moving the deadline from July 27 to August 26, 2026. The extension covers Docket NHTSA-2026-0728, the notice of proposed rulemaking that would amend FMVSS No. 135 to accommodate vehicles built without manually operated driving controls. NHTSA granted the extension after Varnum LLP requested it, stating that the proposal addresses highly technical subject matter and raises novel questions requiring significant review time.
Highlights
- Comment period extended 30 days to August 26, 2026 (Docket NHTSA-2026-0728, RIN 2127-AN00)
- The docket’s primary document has drawn 61 comments to date
- Stopping distance requirements are unchanged; cold effectiveness test speed remains 100 km/h (62.1 mph)
- Pedal force range of 65 N to 500 N (14.6 lbs to 112.4 lbs) gives way to manufacturer specifications for vehicles without manual controls
What the Proposal Actually Changes
The rulemaking, which drops the manual brake pedal mandate for vehicles designed never to be operated by a human, splits FMVSS No. 135 into two compliance tracks. Vehicles that retain manual driving controls face every existing requirement. Vehicles without them get a parallel set of definitions and test inputs.
| Provision | With manual controls | Without manual controls |
|---|---|---|
| Service brake activation | Foot-operated pedal | On-board systems; external command signals precluded |
| Parking brake control | Hand or foot control | On-board systems |
| Service brake control | The foot-operated pedal | Component translating the electronic braking command into mechanical input |
| Stopping distance measured from | Initial application of force to the control | Initial transmission of an electronic command signal |
| Brake control test input | Pedal force 65–500 N (14.6–112.4 lbs) | Manufacturer specifications |
| Warning telltale placement | In front of and in clear view of the driver | Clear view of all designated seating positions |
| Parking brake telltale | Required on application | Excepted |
NHTSA offers a linear actuator as its example of a service brake control on a pedal-less vehicle: it receives an electronic signal and translates it into physical displacement. The agency notes it may be appropriate to define the term as a vehicle component or subsystem, which would better fit a distributed brake-by-wire architecture where a controller sends command signals to a unit at each wheel. Comment is requested on that alternative.
Why the Telltale Requirement Is Unsettled
NHTSA proposes renaming the brake system warning indicator to a brake system warning telltale, aligning terminology with FMVSS No. 101, and requiring that it be visible from all designated seating positions in a vehicle with no driver’s seat. The agency tentatively rejects the stakeholder position that telltales matter only to a driver, arguing that a passenger uses brake system status to decide whether to begin or continue a trip.
The agency is explicitly unsure this is the right mechanism. It asks whether a screen visible to only some occupants, paired with a gate preventing a trip from starting until an occupant acknowledges the condition, would communicate better than a passive display — and whether a required mobile phone application would suffice in a vehicle with no screens at all.
Friction-Type Parking Brake Requirement Dropped
The proposal removes the friction-type specification for parking brake systems while keeping the requirement that engagement be retained by solely mechanical means. That combination still precludes fully electrically actuated parking brakes, which can lose holding capability on power loss, but opens the door to mechanical drivetrain locks. The holding performance requirement is untouched: five minutes on a 20 percent grade, forward and reverse. The Alliance for Automotive Innovation had asked NHTSA to remove the friction-type requirement.
Housekeeping Removals for Test Engineers
Because FMVSS No. 126 requires ABS on all vehicles subject to FMVSS No. 135, NHTSA proposes deleting the wheel lockup sequence and adhesion utilization procedures at S7.2 and S7.4, along with the torque wheel instrumentation specifications at S6.4.2 and S6.4.3. Sections S7.2 through S7.4 become reserved, and Table 1’s test order is revised accordingly. Five definitions go with them: adhesion utilization curves, brake factor, brake hold-off pressure, braking ratio, and objective brake factor.
The ABS disable prohibition also broadens. Removing the word “manual” leaves S5.3.2 reading that any control to disable ABS, fully or partially, is prohibited. Separately, NHTSA proposes correcting initial brake temperature and pedal force notation errors that entered the Code of Federal Regulations in the October 1, 1997 revision, where lower bounds were printed as maximum rather than minimum values.
Filing a Comment
Comments go to Docket NHTSA-2026-0728 at regulations.gov, must be written in English, and are limited to 15 pages with unlimited attachments. NHTSA will consider late comments to the extent possible. The agency has proposed that any final rule take effect immediately and seeks comment on whether that is appropriate.
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