Federal Motor Vehicle Safety Standards; Air Brake Systems Control Line Pressure Balance

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In response to a petition for rulemaking submitted by Sealco Air Controls, Inc., this notice proposes to amend the control line pressure differential requirements in Standard No. 121, Air Brake Systems, for converter dollies and trailers designed to tow another vehicle equipped with air brakes. The agency has tentatively concluded that the proposed amendments would improve the braking compatibility of such vehicles by allowing the use of a relay valve known as a spool- type low opening valve. The agency does not anticipate any adverse safety consequences resulting from amending the pressure differential requirements.