When your vehicle is stopped but has its engine running, the fuel used is not contributing towards moving the vehicle. This contributes to fuel use inefficiency of the vehicle.

Situations where you may have the engine running but not moving the vehicle include when the car has just been started and getting warmed up, when you are waiting for passengers, at the stop sign, or when you are waiting for the traffic lights to turn green. Of course it may not make sense to do this all the time because, for example, your idling at the stop sign is only until you have room to maneuver yourself onto the road that you are turning into. In this case, the length of idling time is unpredictable. However if this idling time is predictable, then it makes it easier for the decision to turn the engine off.

Traffic lights are cases when the idling period is much more predictable. Cars stopped at the lights will have no recourse but to wait for the light to turn green before they can move forward. The wait for the green light is not consistent but can vary from traffic light to traffic light depending on the implementation, time of day, the traffic situation and the sensor data used by the traffic light system to control the frequency of the lights changing and the wait duration for the lights to change.

Drivers can decide to turn off their vehicles when stopped at the red light to save fuel. However, this means constant monitoring and guessing when they should turn off and on the engines, and contributes to another decision that burdens the vehicle operator. A faulty decision here probably will not contribute to a traffic accident, but certainly make for more irate drivers, and potentially adds to traffic congestion.

Certain parts of Europe and Asia have traffic lights that use visible displays that show the wait time before the red light changes to green. This could be used by the drivers to get ready going from a stopped position, or decide when they should turn the engine off and on again if they choose to do that to save fuel. However, this is not be effective all the time as the display may be blocked by other vehicles, or visibility could be obscured by distance or weather conditions.

The solution proposed here, called the Smart Driving Manager, provides a means to provide the necessary information to the vehicle operator that is effective and reliable. It makes it much easier for the driver to decide on when he should turn the engine off and on again, or it can even be used to achieve the engine shutoff in a more automated and controlled manner using an automatic engine start-stop system.

From the driver’s perspective, the Smart Driving Manager appears as a module that can be attached to a convenient location near the dashboard or the vehicle’s driver’s display area.

In its simplest form, the Smart Driving Manager will indicate the red light timer countdown value when the driver has stopped at the traffic lights. Depending on what that value is the driver can decide to stop or start the engine. For example if the countdown value is higher than 30 seconds, turn the engine off. As the value goes down to 5 seconds, start the vehicle and put it in gear to prepare for the green light.

According to the US Department of Energy, less than about 13% of the energy from the fuel you put in your tank gets used to move your car down the road in urban driving. This number goes up to 20% for more rural driving dues to the reduced congestion, and traffic stops.

The rest of the energy is used for accessories such as air-conditioning, or lost to engine and driveline inefficiencies and idling. It is clear that there still exists significant potential to improve fuel efficiency with advanced technologies (Fig. 1).

In urban driving, standby/idling alone contributes to up to 17% of the energy lost, a number that actually exceeds the fuel energy used to move the vehicle. Being able to accurately predict and use the wait period information correctly at traffic lights and turning off the engine instead of idling at traffic lights will contribute to reducing this standby/idling loss.

There may be some concerns that stopping and restarting the vehicle will consume more fuel and have a negative impact on the vehicle, but modern vehicles that use fuel injection technology instead of carburetors do not have these issues. The typical rule of thumb is if you are going to idle for more than 60 seconds or even 30 seconds, it is more fuel efficient to turn the engine off.

Having a system such as the Smart Driving Manager will offload and automate the much of the decision making process and monitoring required of the driver for the traffic lights changing. This will make the idling shut off technique be more practical and dependable.

Other important benefits include less noise pollution with more engines off and the emission of CO2 into the atmosphere is reduced.