Estimate speed toll (4)
I believe the answer is:
rate
This clue is a triple definition!
'estimate' is the first definition.
(I've seen this before)
'speed' is the second definition.
(rate is a kind of speed)
'toll' is the third definition.
(thesaurus)
(Other definitions for rate that I've seen before include "See 16" , "standard levy" , "Appreciate" , "Give a value to something" , "Amount measures against another" .)