51.10. At what speed may the anti-lock braking system not operate?
UAНа якій швидкості антиблокувальна система може не спрацювати?
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This exam question from the Traffic Rules of Ukraine concerns road safety and the technical features of a car's braking system. It serves as a reminder that even modern electronic driver assistants operate within certain modes and have limitations that are important to consider while driving, especially on slippery surfaces and during low-speed maneuvers.
In essence, it checks understanding of the sections of the traffic rules related to the driver's duties and the technical condition of the vehicle: the driver must know and comply with the Rules (item 1.3), check the vehicle's serviceability before driving (item 2.3 "a"), and the condition of the equipment must comply with the manufacturer's instructions (item 31.1). The Traffic Rules do not contain a specific norm that sets the exact ABS activation threshold, so the theoretical exam tests practical understanding of the system's operation: at very low speeds, wheel speed sensors (especially of the passive type) may provide a weak or unstable signal, which means ABS may not intervene at speeds up to approximately 10 km/h.
The analysis of the answer options comes down to the typical threshold at which ABS in many cars no longer regulates brake pressure due to insufficient sensor signal accuracy: the value up to 10 km/h corresponds to the real logic of the system's operation during the "rolling" to a stop. Thresholds up to 20 or 40 km/h are too high, as at such speeds the wheels rotate fast enough for accurate reading, and the system usually operates normally. In practice, this knowledge helps to correctly assess the braking distance: at the end of stopping on ice or wet surfaces, short-term wheel locking without ABS intervention is possible, so distance and speed should be chosen with a margin.
Clause 1.3
Road users are required to know and strictly comply with the requirements of these Rules, as well as to be mutually courteous.
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, and the correct placement and securing of cargo.
Clause 31.1
The technical condition of vehicles and their equipment must comply with the requirements of standards related to road safety and environmental protection, as well as the rules of technical operation, instructions of manufacturing enterprises, and other regulatory and technical documentation.
The Traffic Rules of Ukraine do not contain a specific clause establishing the exact speed at which the anti-lock braking system (ABS) may not operate; this relates to the features of the equipment and is determined by the instructions of the manufacturer (which is directly mentioned in clause 31.1), and the driver is obliged to ensure the technical serviceability of the vehicle and take its features into account during operation (clause 2.3).
Therefore, the correct answer is "Up to 10 km/h," given that, according to the Traffic Rules, the technical condition and equipment of the vehicle must comply with the manufacturer's instructions, and the Rules do not establish any other regulatory threshold for ABS operation.
The anti-lock braking system (ABS) operates when, during braking, it monitors the rotational speed of each wheel and, if necessary, briefly reduces and then increases the brake pressure again so that the wheel does not go into complete lock-up. For this, the system requires accurate data from the wheel sensors.
At very low vehicle speeds, the wheels rotate slowly, and the rotation sensor (especially of the passive type, which is common on many cars) may transmit a weak or unstable signal. In such a situation, the electronic control unit is not always able to reliably determine the moment when locking begins, so it may not activate brake regulation or may disable it as incorrect.
In practice, this manifests as follows: while "rolling up" to an obstacle or when stopping on a slippery section, when the speed is already nearly zero, the ABS may not intervene, and the wheel can briefly lock up. This is not a brake malfunction, but a feature of the system's operation at low speeds due to limitations in the accuracy of the sensor signals.
Therefore, the correct answer is "Up to 10 km/h," since at such a low speed the wheel rotation sensors may provide insufficiently accurate signals, and the ABS may not activate brake regulation.