| Terminology | |
Control or Service Line |
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| The air lines in the trailer air brake system that control the variable strength braking of the vehicle from the tractor foot valve or hand valve. Control or service lines are commonly associated as the blue air line in a braking system. 'Control' is a post FMVSS 121 term and 'Service' is a pre FMVSS 121 term. | |
| Terminology Index |