Interpretation ID: nht74-2.16

DATE: 11/14/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Hall and Myers

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your October 23, 1974, question whether the language of S5.3.1(b) and S5.3.2(b) in Standard No. 121, Air brake systems, exempts all liftable, nonsteerable axles from the "no lockup" requirements of the standard. You specifically ask whether a liftable, nonsteerable "tag" axle and "pusher" axle would be exempt if they were both mounted on a vehicle equipped with a single nonliftable, nonsteerable axle or with tandem nonliftable, nonsteerable axles.

The sections in question permit "lockup of wheels on nonsteerable axles other than the two rearmost nonliftable, nonsteerable axles on a vehicle with more than two nonsteerable axles." This language is limited to vehicles which have more than two nonsteerable axles and therefore a liftable axle on a vehicle with only one other nonsteerable axle would not be exempt. Such combination can be found on some intercity buses.

In both of the examples you described the vehicle has more than two nonsteerable axles, and therefore the language of S5.3.1(b) and S5.3.2(b) would exempt the tag and pusher axles from the "no lockup" requirements of the standard. I would like to emphasize, however, that our language is intended to require "no lockup" performance on not less than two nonsteerable axles of any vehicle with at least two nonsteerable axles. We did not contemplate the unlikely configuration of a single fixed axle and two liftable axles which you cite as an example. If a safety problem arises with this configuration, we would consider an amendment of the standard to require "no lockup" performance of two of these axles.

Yours truly,

ATTACH.