In addition to the safety hazards, what are some other drawbacks of multi-tasking while driving?

Research shows that drivers talking of the phone while driving, even with the use of a hands-free headset, are four times more likely to crash than non-chatters. Yet, many companies design jobs that encourage multi-tasking on the road. In addition to the safety hazards, what are some other drawbacks of multi-tasking while driving? What are the implications of those drawbacks for HR as it designs jobs?