When we design an interfaces, whether they are for web applications or car dashboards, we think about the user. What information is most important, allowing the user to complete the most important task, and what isn't? What information is relevant at which points in a task sequence, and how can the interface scale on demand, providing more information or functionality only when it is needed?
As an anecdote (aha!) we recently conducted a four-cell test on variations of a page for AddThis. Sure enough, the simplest page increased conversion (the user completed the primary task) by a very large and statistically significant amount.
Fewer distractions are good, and simple works. For a great discussion of this phenomena, check out The Paradox of Choice by Barry Schwartz.
So, bringing this back to driving: please, the next time you're behind the wheel, hang up the phone, put down the map,
Less is more.
Study: Distractions, not phones, cause car crashes | Signal Strength - CNET News