In 2011, the National Transportation Safety Board (NTSB) called for a nationwide ban on driver use of portable electronic devices while operating a motor vehicle. The requested ban included prohibiting drivers from using hands free cell phones while driving. Why? Because statistical data shows that even when drivers have hands free cell phones, they still perform visual manual tasks involving their phones which take their eyes off the road.
Here’s a link to the NTSB announcement: https://www.ntsb.gov/news/press-releases/Pages/No_call_no_text_no_update_behind_the_wheel_NTSB_calls_for_nationwide_ban_on_PEDs_while_driving.aspx
Here’s a link to a National Highway Traffic Safety Administration (NHTSA) report on hand held and hands free cell phone usage: https://www.distraction.gov/downloads/pdfs/the-impact-of-hand-held-and-hands-free-cell-phone-use-on-driving-performance-and-safety-critical-event-risk.pdf