Researchers have been tracking the use of phones by drivers for several decades. We know that phones reduce driver performance, and that one fifth of motor-vehicle accidents involve mobile phone use. Heavy traffic and stop-and-go traffic compound the risk, because driving in this type of traffic requires more attention.
The task itself is also relevant. In Japan, dialling and talking while driving was involved in about one sixth of accidents, whereas attempting to locate the phone when it chimes to announce an incoming text message or voicemail was involved in almost half of phone-involved accidents. In addition, laws restricting phone use do little—at this stage—to reduce actual cell-phone use. This research applies not only to you and me, but also to professional drivers.