A US take on proportionality. Justice White said,

‘The Department of Transportation accepts the applicability of the “arbitrary and capricious” standard. It argues that under this standard, a reviewing court may not set aside an agency rule that is rational, based on consideration of the relevant factors and within the scope of the authority delegated to the agency by the statute. We do not disagree with this formulation. The scope of review under the “arbitrary and capricious” standard is narrow and a court is not to substitute its judgment for that of the agency. Nevertheless, the agency must examine the relevant data and articulate a satisfactory explanation for its action including a
“rational connection between the facts found and the choice made.”…

In reviewing that explanation, we must
“consider whether the decision was based on a consideration of the relevant factors and whether there has been a clear error of judgment.”…

Normally, an agency rule would be arbitrary and capricious if the agency has
[a] relied on factors which Congress has not intended it to consider,
[b] entirely failed to consider an important aspect of the problem,
[c] offered an explanation for its decision that runs counter to the evidence before the agency, or
[d] is so implausible that it could not be ascribed to a difference in view or the product of agency expertise.

The reviewing court should not attempt itself to make up for such deficiencies:
“We may not supply a reasoned basis for the agency’s action that the agency itself has not given.”… We will, however,
“uphold a decision of less than ideal clarity if the agency’s path may reasonably be discerned.”… For purposes of these cases, it is also relevant that Congress required a record of the rulemaking proceedings to be compiled and submitted to a reviewing court…and intended that agency findings under the Act would be supported by
“substantial evidence on the record considered as a whole.”…’

[Edited and formatted for ease of reading. Matter in square parentheses added.] You can find this report on Westlaw International.