Ordinary regulation of train speed (10)
I believe the answer is:
pedestrian
'ordinary' is the definition.
(thesaurus)
'regulation of train speed' is the wordplay.
'regulation of' indicates an anagram (I've seen 'regulation' mean this).
'train'+'speed'='trainspeed'
'trainspeed' is an anagram of 'PEDESTRIAN'.
(Other definitions for pedestrian that I've seen before include "One walks around" , "Hiker" , "lame" , "Dull, uninspired" , "Boring" .)