Ask an expert

My husband always turns off the ignition at traffic lights to save fuel and also to help the environment, I honestly think and there is more pollution by re-starting the engine instead of leaving it running. Can you settle this disagreement for me, it drives me insane! Also at what point do you think it necessary to turn off ignition....if stopping for 3 mins; 10 mins etc.

I’m going to sit on the fence here a little.

Stop/Go technology is becoming common place within the car industry which automatically does what your husband is doing.

There are certain parameters which need to be met however to allow this system to work. When the engine is cold for example it does not work while the engine management system is always looking at other factors such as vehicle speed. There are times when the engine does not shut down.

The other point is the engine automatically restarts while your husband has to be at the ready so to speak and would need to have the clutch disengaged if the car is a manual, or move the gear selector to Park or Neutral if it’s an auto.

I would not be keen on carrying out this operation on an auto to be honest as they are best left in Drive at traffic lights etc.

The other important point is the wear and tear on the starter motor. The cars that have this technology will have starters that are designed to cope with the constant work load whereas your car has not been designed with such a starter motor.

There will also be other features on the modern motor vehicle to reduce fuel consumption, the Stop/Go technology is only one such feature.

Overall I don’t believe the savings would be huge (if any) in your case unless the stops are in excess of around 3 to 4 minutes on a regular basis. More fuel can be saved by keeping the tyre pressures set correctly, the engine in a good state of tune and if the car is driven with a smooth throttle operation.