There may be something later but:

SMART
Technical Specification for
Diesel Multiple Units (DMUs)
Draft for Industry Review
January 20, 2010
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Big cut
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4.4.1
The coupler system shall be service proven and shall meet the requirements of
49 CFR 229.61, 238.205, and 238.207, as well as all applicable APTA and AAR
Standards and Recommended Practices. The cab ends of the cars shall have an
automatic coupler system that will make all mechanical, pneumatic, and electrical
trainline connections when mated. The non-cab ends of the cars shall have either
an automatic coupler or a semi-permanent drawbar. If a semi-permanent
drawbar is used, electrical and pneumatic connections shall use connectors that
allow the two halves of a married pair to be separated in a shop environment.
The proposed coupler system design shall be submitted to SMART prior to car
construction [CDRL 4-1].
The coupler connections shall permit operation of up to four vehicles in a train
under normal conditions through electric and pneumatic trainlines. Coupler
controls shall be located in each operator’s cab and outside the vehicle near
each automatic coupler.
The coupler and draft gear shall have the strength needed to allow, under
emergency conditions, a train of four vehicles with an AW3 passenger load to
push or pull an inoperable train of up to four vehicles with an AW3 passenger
load, without damage to the coupler or its anchorage.
Each coupler shall have a carrier that maintains nominal coupler height while
allowing vertical dynamic motion. Each coupler shall have an automatic
horizontal centering device that aligns an unloaded coupler to carbody centerline.
The coupler carrier and centering device shall be adjustable to allow
maintenance personnel to correct for wheel, truck, suspension, and carbody
wear. The coupler location shall be maintained within 1-1/2 inches vertically and
1-1/2 inches horizontally of its nominal position on level, tangent track with new
wheels under all static conditions from AW0 to AW3. Coupler adjustment shall
not be required more frequently than 92-day intervals.
Coupler gathering range shall be a minimum of 3-3/4 inches of misalignment
between opposing coupler centerlines. The coupler gathering range shall be
sufficient for two cars to automatically couple on tangent track when each coupler
is maintained within the above stated tolerance. Likewise, two cars shall be able
to couple on a 12.5 degree horizontal curve.

And later:

4.2
Tow Provisions
The following provisions shall be provided to permit rescue by a standard
locomotive.
4.2.1
Coupler Adapter
Each car shall be equipped with one coupler adapter to allow the commuter rail
vehicles to be connected to a conventional AAR type-E, F, or H coupler. The
removable adapter shall have a maximum weight of 65 pounds and be normally
stored on the F-end pilot. It shall be able to withstand 100,000 pounds in buff or
draft without permanent deformation. The operator shall be able to manually
install or remove the adapter alone and without tools. The adapter is anticipated
to be used only during emergency or rescue situations.
4.2.2
Pneumatic Connections
Provision shall be made to permit a standard locomotive to connect to the control
pressure (brake pipe) pneumatic trainline when the coupler adapter is used to
move the commuter rail vehicle. In addition to the automatic coupler pneumatic
connections, the control pressure (brake pipe) pneumatic trainlines shall be piped
to a location adjacent to the coupler with cut-out cocks and fittings to allow
application of a standard brake pipe hose with glad hand. The geometry shall
allow coupling to a locomotive brake pipe hose. One hose with fittings shall be
provided with each commuter rail vehicle.