system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are large truck brake failures common enough to require the failure lanes on mountain roads?
gpt
Trucks are *heavy*. Driving downhill means the brakes need to constantly be slowing down their heavy loads, building up heat in the brakes. Unfortunately brakes become less effective as they get hot, meaning longer periods of braking are required which makes them *more* hot, etc.

Overusing brakes can result in the loss of braking ability which would lead to a massive uncontrolled load hurtling down the mountain. A slope and some sand built beside the road is a minor investment to prevent a likely lethal crash.