A review of more than 100 different cell phone studies using either tracking devices on actual vehicles or carefully crafted simulations revealed that nearly all volunteers showed impairment due to cell phone usage. Mental distraction accounted for the vast majority of these performance issues, with phone conversations increasing reaction time, speed, steering wheel adjustments, and total lane deviations. An aggregate analysis of other studies showed similar results on two separate occasions.
Older drivers in particular were found to be more susceptible to driving impairment when using a cell phone. As few studies incorporated drivers under the age of 18, there is not enough data to come to a conclusion regarding teenage drivers. Reports are also conflicted as to whether driving while handling a cell phone improves with practice. Some preliminary studies have implied that the negative effects associated with cell phone usage can diminish with experience.
Employing a functional MRI machine, university researchers discovered that overall brain activity attenuated by 37% when subjects, wearing headsets, listened and responded to statements made while using a driving simulator. According to the report, a phone conversation can sap cognitive resources away from driving, damaging driving performance regardless of whether a phone is being held.
In addition to driving simulations, observational studies have been done to record real world driving habits. One study fastened video cameras and monitoring devices to one hundred vehicles in order to capture data. Of the 100 cars there were only a couple of serious accidents, yet by incorporating the number of near-collisions researchers were able to conclude that cell phone use nearly tripled the risk of a crash. Odds of a near crash were 1.3 times more likely as well. Of these incidents, using a handheld phone increased the risk by only 4%, with dialing on a handheld constituting only a fraction of the total cell phone use.