55.26. At what speed may the anti-lock braking system fail to operate?
UAНа якій швидкості антиблокувальна система може не спрацювати?
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This exam question from the Traffic Rules of Ukraine concerns braking safety and vehicle controllability in real driving conditions. It serves as a reminder that even modern active safety systems have their technical limits, and the driver, during the theoretical exam, must understand how the features of the braking system affect stopping the vehicle, especially on slippery surfaces or during maneuvering.
The question tests knowledge of the section of the Traffic Rules regarding the driver's responsibilities and the choice of a safe speed, in particular the requirements of clause 2.3 (a) regarding the technically sound condition of the vehicle and clauses 12.1 and 12.3 regarding speed control and actions in case of danger. The point is that at very low speeds, the ABS may not activate due to insufficiently accurate signals from the wheel rotation sensors, so the correct answer is the lowest of the proposed thresholds. Options with higher values (up to 20 km/h and up to 40 km/h) are incorrect, because ABS is usually designed to operate at much higher speeds, and the problem arises precisely in the "almost zero" zone, when wheel rotation is difficult to read correctly.
The practical significance of this for the traffic rules is simple: when smoothly approaching a stop line, in a traffic jam, or during emergency braking leading to a complete stop, the driver should not rely on ABS always "backing up" in the last meters. This knowledge helps to adequately assess the condition of the vehicle, maintain a safe distance, choose speed considering the road surface, and be prepared for the fact that at minimal speed, brief skidding or partial wheel lock-up is possible even in a properly functioning vehicle.
Clause 2.3 (subclause "a")
To ensure road safety, the driver is obliged: before driving, to check and ensure the technical serviceability and completeness of the vehicle, as well as the correct placement and securing of the load.
Brief application: the question tests understanding that braking efficiency depends on the condition and features of the braking systems (in particular ABS), and the driver must take into account that certain systems may operate with limitations at very low speeds.
Clause 12.1
When choosing a safe driving speed within the established limits, the driver must take into account the road situation, as well as the characteristics of the cargo being transported and the condition of the vehicle, in order to be able to constantly control its movement and drive it safely.
Brief application: knowledge that ABS may not operate at low speeds relates to considering the “condition of the vehicle” and its actual capabilities during braking.
Clause 12.3
If a danger to traffic or an obstacle that the driver can objectively detect arises, he must immediately take measures to reduce speed up to stopping the vehicle or safely maneuvering around the obstacle for other road users.
Brief application: when reducing speed up to a stop, the driver should understand that in the “almost zero” speed range, ABS may no longer intervene, and braking/handling may change.
That is, the correct answer is "Up to 10 km/h," given that according to the traffic rules, the driver is obliged to ensure the technical serviceability of the vehicle and, when choosing speed, to take into account the condition and actual capabilities of the braking systems, in particular the limitations of ABS operation at very low speeds.
The anti-lock braking system (ABS) is needed to prevent the wheels from fully locking during intensive braking, allowing the vehicle to remain controllable. Its operating principle is based on constantly monitoring the rotational speed of each wheel and briefly adjusting the braking force when the system "detects" signs of locking.
For ABS to correctly determine whether a wheel is starting to stop, the sensors must read the rotation with sufficient accuracy. At very low wheel rotation speeds, the signal from the sensor may be unstable or insufficiently informative for reliable detection of locking. In such a situation, the system may not activate because it does not receive the correct data to control the pressure in the brake drive.
In practice, this occurs during almost complete stops: for example, when you are braking before a stop line or approaching an obstacle at minimal speed. In these last few meters, the ABS may no longer intervene, and brief skidding or wheel locking is possible, even if the vehicle is technically sound.
Therefore, the correct answer is "Up to 10 km/h," since at such a low speed the wheel rotation sensors may not provide a sufficiently accurate signal, and the ABS may not activate.