Roadside accommodation is that speck of dust on the left (5)
I believe the answer is:
motel
'roadside accommodation' is the definition.
(I've seen this before)
'that speck of dust on the left' is the wordplay.
'that speck of dust' becomes 'mote' (I've seen this before).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'the left' becomes 'L' (common abbreviation).
'mote'+'l'='MOTEL'
'is' is the link.
(Other definitions for motel that I've seen before include "somewhere to stay the night" , "Accommodation for road travellers" , "Lodging for drivers" , "Kind of hostelry for car drivers" , "Place for motorists to stay" .)