Force to cover two miles in traffic (8)
I believe the answer is:
commerce
'traffic' is the definition.
(I've seen this before)
'force to cover two miles' is the wordplay.
'two miles' means two replacements for 'miles'.
'force' becomes 'coerce' (synonyms).
'to cover' is an insertion indicator.
'miles' becomes 'm' (common abbreviation).
'miles' becomes 'm' (common abbreviation).
'm'+'m'='mm'
'coerce' going around 'mm' is 'COMMERCE'.
'in' is the link.
(Other definitions for commerce that I've seen before include "The buying and selling of commodities and services" , "Business, industry, trade" , "Activity of buying and selling" , "The buying and selling of goods and services" , "Business dealings" .)