Beyond checking that they are connected and not leaking, what does a driver verify about the air lines running to the trailers of a double or triple?

Explanation

The driver confirms that the air lines are supported and fastened with just enough play to allow for turns, and that none of the lines are damaged. The slack requirement is the part that is easy to get backwards: an articulated combination changes the distance and the angle between its units every time it turns, so a line with no spare length is a line that will be stretched or torn off at the first tight corner, while a line with too much unsupported length can sag into the drivetrain or onto the road. 49 CFR 383.111(a)(17)(iii) names coupling system defects among the safety-related items a driver must know to look for, but it does not state this check, so it is attributed to the manual. The wrong options either destroy the slack that turning requires, as pulling the lines taut and clamping them rigidly at both ends both do, or confuse the air lines with a different system, since they are not routed through the dolly's tank as a filter.

Source: 49 CFR 383.111(a)(17)(iii)