Assistance to motorists so GPS isn't misused? (9)

I believe the answer is:

signposts

'assistance to motorists' is the definition.
(road signs give motorists information)

'so gps isn't misused?' is the wordplay.
'misused?' indicates anagramming the letters.
'so'+'gps'+'isnt'='sogpsisnt'
'sogpsisnt' anagrammed gives 'SIGNPOSTS'.

(Another definition for signposts that I've seen is " Guides, by the way".)

I've seen this clue in The Times.

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