What slows up journey having dropped off Bobby? (17)
I believe the answer is:
sleepingpoliceman
'what slows up journey having dropped off bobby?' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'off bobby?' is the wordplay.
'off' becomes 'sleeping' (I can't explain this - if you can you should give a lot more credence to this answer).
'bobby?' becomes 'policeman' (bobby is a kind of policeman).
'sleeping'+'policeman'='SLEEPINGPOLICEMAN'
Can you help me to learn more?
(Another definition for sleepingpoliceman that I've seen is " hump".)