When must trailers and semi-trailers have brakes that can be applied by the driver?

The correct answer is based on regulations concerning the braking requirements for trailers and semi-trailers. According to the guidelines, trailers and semi-trailers must be equipped with brakes that the driver can operate when the gross weight reaches 4,500 pounds. This ensures that the trailer can be effectively controlled and stopped, supporting safety on the road, especially as the weight of the trailer increases.

When a trailer or semi-trailer is at or above this weight, having a braking system that can be applied by the driver is crucial for maintaining safe stopping distances and preventing potential accidents. This regulation is designed to safeguard not only the driver but also other road users by ensuring that larger, heavier units can be stopped adequately in emergency situations.