In the present research, we investigated the hypothesis that working memory mediates conversation-induced impairment of situation awareness (SA) while driving.
The principle is quite simple. Driving requires working memory, specifically the phonological loop. So does conversation. If you are doing more of the latter, you have less working memory to allocate to the former and performance will degrade. And sure enough, that is exactly what they found.
This is important because so many people still claim that handsfree cell phone use makes it safe for driving. We are incorporating all kinds of technology into our cars and thinking that it is safe as long as it is controlled with speech rather than manually. Not only is this a myth, it is a dangerous myth. Any task that requires working memory is going to degrade performance and it should be locked out (or at least minimized) while the car is in motion.
Driverless cars, where art thou!!!