Perhaps with walkers on street, one should stop motorists (3,5)
I believe the answer is:
'stop motorists' is the definition.
'red light' can be an answer for 'stop' (I've seen this before). I am not sure about the 'motorists' bit.
'perhaps with walkers on street one should' is the wordplay.
I cannot really understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for red light that I've seen before include "sleazy" , "Danger sign" , "Stop signal" , "Illumination indicating danger" , "Warning signal" .)