Driving while using a cellphone is a form of distracted driving, reducing the driver's awareness of his surroundings and increasing his reaction time. Approximately one out of four car crashes involves cellphone use.
One study found that participants using a cellphone exhibited delayed braking reactions and were involved in more accidents than when they did not have a cellphone. Several studies have also found that driving impairment due to cellphone use occurs regardless of whether the cellphone is a hands-free or handheld device. Lastly, talking on a cellphone causes impairment to drivers' peripheral vision, rendering them blind to objects they would normally see, such as a person in a crosswalk).