PART 393--PARTS AND ACCESSORIES NECESSARY FOR SAFE OPERATION
 
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1. The authority citation for part 393 continues to read as follows:
 
    Authority: Section 1041(b) of Pub. L. 102-240, 105 Stat. 1914; 
49 U.S.C. 31136 and 31502; and 49 CFR 1.73.
 
 
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2. Amend Sec.  393.5 by adding a new definition for ``Surge Brake'' in 
alphabetical order to read as follows:
 
 
Sec.  393.5  Definitions.
 
* * * * *
    Surge Brake. A self-contained, permanently closed hydraulic brake 
system for trailers that relies on inertial forces, developed in 
response to the braking action of the towing vehicle, applied to a 
hydraulic device mounted on or connected to the tongue of the trailer, 
to slow down or stop the towed vehicle.
* * * * *
 
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3. Amend Sec.  393.40 by adding paragraph (b)(5), a new specification 
of ``Surge brake systems,'' to read as follows:
 
 
Sec.  393.40  Required brake systems.
 
* * * * *
    (b) * * *
    (5) Surge brake systems. Motor vehicles equipped with surge brake 
systems must have a service brake system that meets the applicable 
requirements of Sec. Sec.  393.42, 393.48, 393.49, and 393.52 of this 
subpart.
* * * * *
 
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4. Amend Sec.  393.48 by revising paragraph (a) and adding paragraph 
(d) to read as follows:
 
 
Sec.  393.48  Brakes to be operative.
 
    (a) General rule. Except as provided in paragraphs (b), (c), and 
(d) of this section, all brakes with which a motor vehicle is equipped 
must at all times be capable of operating.
    (b) * * *
    (c) * * *
    (d) Surge brakes. (1) Surge brakes are allowed on:
    (i) Any trailer with a gross vehicle weight rating (GVWR) of 12,000 
pounds or less, when its GVWR does not exceed 1.75 times the GVWR of 
the towing vehicle; and
    (ii) Any trailer with a GVWR greater than 12,000 pounds, but less 
than 20,001 pounds, when its GVWR does not exceed 1.25 times the GVWR 
of the towing vehicle.
    (2) The gross vehicle weight (GVW) of a trailer equipped with surge 
brakes may be used instead of its GVWR to calculate compliance with the 
weight
 
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ratios specified in paragraph (d)(1) of this section when the trailer 
manufacturer's GVWR label is missing.
    (3) The GVW of a trailer equipped with surge brakes must be used to 
calculate compliance with the weight ratios specified in paragraph 
(d)(1) of this section when the trailer's GVW exceeds its GVWR.
    (4) The surge brakes must meet the requirements of Sec.  393.40.
 
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5. Revise Sec.  393.49 to read as follows:
 
 
Sec.  393.49  Control valves for brakes.
 
    (a) General rule. Except as provided in paragraphs (b) and (c) of 
this section, every motor vehicle manufactured after June 30, 1953, 
which is equipped with power brakes, must have the braking system so 
arranged that one application valve must when activated cause all of 
the service brakes on the motor vehicle or combination motor vehicle to 
operate. This requirement must not be construed to prohibit motor 
vehicles from being equipped with an additional valve to be used to 
operate the brakes on a trailer or trailers or as required for busses 
in Sec.  393.44.
    (b) Driveaway-Towaway Exception. This section is not applicable to 
driveaway-towaway operations unless the brakes on such operations are 
designed to be operated by a single valve.
    (c) Surge brake exception. This requirement is not applicable to 
trailers equipped with surge brakes that satisfy the conditions 
specified in Sec.  393.48(d).