Add this code to categories, but do not include an extra newline before the
<noinclude>, and you use the infobox name for sorting:
<noinclude> [[Category:Infobox templates|Passengers]] </noinclude>
Where Passengers may be, for example, used for "Infobox Passengers".
If you would like the infobox to force every page that includes it to be in a certain category, use the
<includeonly> tags instead.