When are trailer brakes essential to have operational?

Trailer brakes are essential to have operational primarily when the trailer has no spring brakes. Spring brakes are a type of safety mechanism that engages automatically to slow down or stop a trailer if air pressure drops. If a trailer is equipped with spring brakes, they can assist in maintaining control and safety even in situations where the primary brakes fail. However, trailers without these spring brakes rely entirely on their regular braking system to stop the vehicle effectively. Having operational brakes in such cases is crucial to ensure that the trailer can be controlled and brought to a stop safely, especially in various driving conditions.

The other choices do not adequately capture the necessity of having operational trailer brakes. For instance, implying that brakes are only needed for daytime driving disregards the importance of safety at night or in poor weather. Mentioning flat surfaces fails to account for the variability in road conditions that might require effective braking. Lastly, while trailer brakes are certainly important during long downhill drives due to increased braking demands, the need for them extends beyond just that scenario and is critical in any situation where a trailer is being towed without spring brakes.