Talking on a hands-free mobile while driving raises the risk of having a rear-end shunt, scientists warn. A new study has found that motorists‘ brains become overloaded during phone conversations, costing them milliseconds of reaction time when the car in front brakes sharply. And it makes no difference whether they are using legal hands-free kits or breaking the law by having the handset clamped to the side of the head. Researchers from the Universities of Central Florida and Beijing Jiaotong selected 42 men and women aged between 30 and 40 and with driving licences. They were put behind the wheel of a car on a driving simulator and asked to negotiate an urban dual carriageway behind a vehicle driving at 50 kph (31 mph), which then slows to 40 kph (25 mph) before stopping suddenly. Each participant had three sessions in the simulator so they could perform emergency stops while holding a mobile to their head, while talking hands-free and without distraction – though the running order was chosen at random. To mock up the effects of having a conversation, drivers had to respond to a series of maths questions played over a speaker. Of the 126 emergency stops, seven ended in rear-end shunts, all of them involving mobile use, four of them hands-free. There were a further 15 near-misses – twelve of them involving mobiles, seven of them hands-free. Drivers with no distractions were faster to react when there was a large gap between the vehicles and quicker to apply the brakes. Those on the phone were quicker to spot danger when the cars were closer together and braked harder, suggesting that those using mobiles were aware that what they were doing was dangerous and so over-compensated. […]