What physiological effect does using a handheld mobile phone while driving have on driver performance?

1. It causes significant cognitive distraction, doubles reaction time, impairs lane keeping, and increases collision risk by four times
2. It improves alertness by keeping the driver awake during long journeys
3. It has no measurable impact on driving as long as the driver holds the steering wheel with one hand
4. It only distracts drivers when reading text messages, but not during voice phone calls