Should an automatic car be shifted to neutral when waiting at a traffic light?
3 Answers
Automatic cars should be shifted to neutral when waiting at a traffic light. Shifting to neutral gear while waiting, combined with using the handbrake, is safer. Engaging N gear and applying the handbrake can save fuel to some extent, as the passive wheel in the torque converter of the transmission is in an idling state, which doesn't increase engine operation, thereby reducing fuel consumption. When using P gear to wait at a traffic light, shifting from P to D gear can easily cause a reversing phenomenon, which may affect the driving of the vehicle behind and, in severe cases, lead to a rear-end collision. When waiting at a traffic light in D gear with the foot brake applied, since the passive wheel in the torque converter between the engine and the transmission is fixed, a counterforce is generated and applied to the active wheel, increasing the load on the engine. This can be understood as hindering the engine's operation, causing the engine ECU to increase fuel injection, resulting in higher fuel consumption.
When waiting at a red light in an automatic car, whether to shift to neutral or not depends on habit and the duration of the red light. As an experienced driver with eight years behind the wheel, I find it most convenient to just press the brake and stay in D gear for short red lights—it's quicker to start within thirty seconds and hassle-free. However, if the red light lasts over a minute, I usually shift to neutral and engage the handbrake, which allows my leg to relax and relieves strain on the transmission. The key is to watch out for rolling, especially on slopes—the brake must be firmly pressed. Occasionally, I hear that shifting to neutral can save a bit of fuel, but my tests show minimal difference. Though, the engine does sound a bit smoother.
When waiting at a red light during daily driving, safety should always come first. When an automatic transmission vehicle is in D gear with the brake pedal pressed, the car is in a semi-engaged clutch state. In case of a rear-end collision, this may damage the transmission gears. I always emphasize this point when teaching beginners, recommending to shift to neutral for red lights lasting more than twenty seconds while developing the habit of engaging the electronic parking brake. Although it adds one more step when starting off, it prevents damage to the drivetrain system and saves on repair costs in the long run. Don't forget to check if the brake lights are functioning properly, as this affects whether the following vehicle can react in time.
