Fewer taxi drivers are willing to work the night shift because of concerns for their safety.
Just over a third of those surveyed by the National Transport Authority said they work between midnight and 4 am.
Jim Waldron from the National Private Hire and Taxi Association says taxi ranks at night can be intimidating.
"There are disputes because there would be drink or drugs consumed by the passenger and there might be a dispute about the route or the fare at the end of the journey in general.
Every taxi driver encounters some problems throughout the week."
Personal safety was the main reason given, followed by health, while one in ten said it just wasn't worth their while financially.
He added: "This can be offset if there were better locations for taxi ranks. If investment in lighting at ranks were to be made available and more drivers might consider using them if the ranks were supervised.".
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