Carmakers are rolling out a growing number of functions available in smart vehicles, but some of them require too much attention on the displays and may cause visual distraction, said J.D. Power on Thursday.

Such functions may result in accidents and should only be available when the vehicles are safely parked, said the company in a report in collaboration with Tongji University's HVR Lab.

The report also urged carmakers to pick out functions that have little to do with driving in the early stage of development to prevent potential dangers, adding that safety is the top priority for vehicles.

Also, J.D. Power and Tongji's HVR Lab found that customers are less satisfied with smart onboard functions despite their growing number, which may be the result of car buyers' higher anticipation.

The interior design has gone monotonous, featuring usually a horizontally positioned 15-inch or 16-inch central display, so it causes less excitement.

The report said sliding displays can become a new trend as they offer better experience.

It also said the use of head-up displays is gaining momentum, adding that it can help improve driving safety as the drivers can focus on the road ahead.