Which color represents the emergency line in a truck's braking system?

The emergency line in a truck's braking system is represented by the color red. This line is crucial for ensuring the vehicle can stop safely in the event of a failure with the service brake system. The red emergency line typically connects the tractor's air supply to the trailer's braking system, allowing the emergency brakes to be engaged if the connection is broken or if the air pressure drops below a certain level.

Red is universally recognized as a color indicating danger or caution, which aligns with the importance of the emergency braking system in maintaining safe operations on the road. In the context of a CDL pre-trip inspection, understanding the color coding of brake lines is vital for truck drivers to quickly identify and troubleshoot any potential issues with the braking system. This knowledge helps ensure that the vehicle is safe and compliant before operating on public roads.