Ford has developed a system that can work out when it is an especially bad time to take use an in-car phone and block the call temporarily.

The idea is that if, say, you are coming down a slip road and about to join a busy motorway, you don't want to be answering a call while trying to simultaneously look in your mirrors.

A Ford spokesman said, "We're researching ways to use the car's own intelligence to further help drivers. Vehicle control inputs, sensors, road conditions and biometric information such as a driver's pulse and breathing can all be used to create a driver workload estimation."

Basically, that means the system would calculate how hard the car is working, how stressed the driver is, and how busy the road conditions are, before allowing the phone to receive a call. A lot of the required sensors are already available – for example the Blind Spot Information System already detects traffic approaching the rear of the car, and traction control and ABS system continually monitor the behaviour of the vehicle.

The only new area would be measuring driver biometrics. This would be done via sensors in the steering wheel to get information about heart-rate – like the metal pads in some gym equipment. Adding a sensor in the seatbelt would enable measurement of breathing and a final sensor would compare ambient temperature in the cabin to the driver's temperature to check if the driver is getting hot and bothered.

At present, it is only a prototype, but one can see the value in the idea.