I was able to locate the document referred to in a Public Comment on the underride rulemaking. See this post: A Public Comment on Underride Rulemaking re: original intent of NHTSA in 1969
The Public Comment was asking for NHTSA to extend underride protection to the sides of trucks and mentioned that it was the original intent of the underride rulemaking in 1969. This is what the Federal Highway Administration said at that time,
It is anticipated that the proposed standard will be amended, after technical studies have been completed, to extend the requirement for underride protection to the sides of large vehicles.
Imagine! In 1969.
And NHTSA said this, in response to our petition request in 2014 to add side guards:
By initiating rulemaking to consider enhancing related safety standards, this notice grants the part of the petition for rulemaking submitted by Ms. Marianne Karth and the Truck Safety Coalition (Petitioners) requesting that the agency improve the safety of rear impact (underride) guards on trailers and single unit trucks. Based on the petition, available information, and the agency’s analysis in progress, NHTSA has decided that the Petitioners’ request related to rear impact guards merits further consideration. Therefore, the agency grants the Petitioners’ request to initiate rulemaking on rear impact guards. NHTSA is planning on issuing two separate notices—an advanced notice of proposed rulemaking pertaining to rear impact guards and other safety strategies for single unit trucks, and a notice of proposed rulemaking focusing on rear impact guards on trailers and semitrailers. NHTSA is still evaluating the Petitioners’ request to improve side guards and front override guards and will issue a separate decision on those aspects of the petition at a later date.
Here is that 1969 document:
This was the original intent of NHTSA rulemakers in the 1969 NPRM, Docket No. 1-11; Notice 2.
Imagine. . . when I was 13 years-old in 1969, DOT was doing proposed rulemaking on underride and “anticipated that the proposed Standard will be amended, after technical studies have been completed, to extend the requirement for underride protection to the sides of large vehicles.”
And what has happened between now and then? Certainly not any mandated, and very little voluntary, side guard protection on trucks.
NHTSA mentioned side guards in their response to our 2014 petition to them: A Proposed Rule by the National Highway Traffic Safety Administration on 07/10/2014