Foot a self-declaration by public transporter (6)
I believe the answer is:
iambus
'foot' is the definition.
(I know that iambus is a type of foot)
'a self-declaration by public transporter' is the wordplay.
'a self declaration' becomes 'iam' (I can't justify this - if you can you should give a lot more credence to this answer).
'by' is a charade indicator (letters next to each other).
'public transporter' becomes 'bus'.
'iam'+'bus'='IAMBUS'
Can you help me to learn more?
(Other definitions for iambus that I've seen before include "Metrical foot" , "poetic form" , "Metrical unit of two syllables" , "Type of metrical unit in a poem" .)