The 36-year-old Czech national was arrested on Saturday.
6 Still In Hospital After Fatal Ayrshire Bus Crash
Six people remain in hospital following a double-decker crash in which a 45-year-old female passenger was killed.
The Stagecoach bus was involved in a collision with a 4x4 near the seaside town of Ardrossan in North Ayrshire on Monday afternoon.
Both male drivers, aged 36 and 48, are in a serious but stable condition in Glasgow's Queen Elizabeth University Hospital following the crash, which happened at around 2.15pm.
Four bus passengers are being treated at Crosshouse Hospital in Kilmarnock and a further five have been released following treatment.
Police are appealing for witnesses to the crash, which happened on the A78 north of Ardrossan, close to the Rowan Tree restaurant.
A 45-year-old woman travelling on the Greenock to Ayr bus died at the scene.
The road was closed for seven hours while investigators assessed the crash site.
Sergeant Kevin Blackley said: "Extensive inquiries are ongoing today into the cause of the crash.
"At this time I would urge anyone who witnessed the crash, who has not yet spoken to police, or anyone with information that may assist our investigation to contact us through the non-emergency number 101.''
A Stagecoach spokeswoman said following the collision: "Our first thoughts are with those affected by this incident.
"The safety of our passengers and staff is our highest priority and we are assisting the police fully with their investigation into the circumstances.''
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