Switching off the engine at traffic lights

null · 21st January 2012, 23:34

Depends how deep your pockets are

Getting back to the topic - I remember reading somewhere that every 5 mins of idling is equivalent to about 1 km of running a vehicle and hence it makes sense to shut down if >1 min.

I switch off the engine even if it is 30 sec to go if there is a huge traffic pile up ahead of me. Usually it takes another 10-15 sec for me to move and hence it is still OK. But I have felt it is not that easy with a diesel car and usually I don't take a chance when I drive my friend's diesel. But then, it probably is so because I am not used to it.

AbhiJ · 22nd January 2012, 00:09

I normally have a 60 second time limit. Over that.. I turn off the engine. Below that, keep it idling...

PM - B · 22nd January 2012, 00:35

It is approximately 3 minutes of idling = 1 KM of travel. According to the FORD Driving Classes For Life.

Why are we asking this question?
1. Fuel Efficiency
2. Life / state of engine

1. We are wasting fuel if the engine is on and the car is stationary.
Hence from the first point, shut of the engine, if the wait is more than 30 seconds.

As has been shared by "null" above, it can take another 10 - 15 seconds for your turn to move once the signal has turned to green.

If the signal does not have a countdown timer, look to see if you are at the very begining of the signal or pretty close to it. This most times will tell you that you will have at least 30 - 60 seconds of wait. In which event switch off.

I have noticed that when i do not shut the engine off at the traffic lights at Bangalore, i have got 14 - 14.5 KM/L efficiency.
When i shut the engine off at the traffic lights, i have consistently been able to get atleast 17 KM / L.

A huge improvement in the FE. Either ways i do shut the engine off.

2. If we are looking at it from the life / state of the engine,
There are two ways to look at it, i am sure the gurus can add on to each in detail

a.This cannot be bad for modern cars, that is, the start stop function of the engine, think, the more expensive hybrid cars have auto start stop function which automatically would do the same.

b. I have read car manuals that state, if you drive in stop and go traffic or less than ~ 10 - 15 KM s, this is considered as stressful for the engine. I assume they also mean this because the engine might not have reached the operating temperature at all OR conversely it causes the engine to heat very rapidly.

speedsatya · 22nd January 2012, 00:46

Anything more than a minute and I switch off the engine completely ( Even the music system goes off )

Rahulkool · 22nd January 2012, 01:51

I never shut off the engine, IMO its not worth the trouble lol and in chennai AC is also essential.

pranavt · 22nd January 2012, 02:13

Quote:

Originally Posted by suhaas307

Also remember that when you start a car, it consumes more fuel than usual.

Only true in case of cold starts, which are not so common when you're stuck in traffic at a signal waiting for your turn. Different engine/coolant temperatures require different amounts of cranking fuel. The hotter the coolant, the lesser the amount of cranking fuel compensation.

Unless the signal's going green in 10-15 seconds and you're first in line, there's no reason to not shut off your petrol engine.

mayankjha1806 · 22nd January 2012, 05:39

How does the whole equation changes if the car is a Diesel one. Unfortunately both my cars are petrol ones and i usually shut the engine off if i see timing anywhere above 30s.

If i have to keep it on for various reasons then i put the car in neutral/handbrake and then wait for the signal to turn green again. I dont think one should stop in a gear and keep the clutch pressed while waiting (When engine is running).

If its day time and hot i usually switch the AC on much before the signal so as when i am at the signal the car is cold already hence no problem for passengers if the AC is switched off for ~a minute.

Nagesh · 22nd January 2012, 07:25

Just to add to how we can judge when there is no indicator at a traffic signal, since i drive along the same route for the daily commute, we can anticipate "our turn" based on which side is passing. Ofcourse if we are way too behind, its a little difficult

dingolphie · 22nd January 2012, 08:15

I'm sorry to say that I'm one of the guys that never switch off, unless it really is a long wait (cars are stuck). In fact I usually idle with a/c when my wife does a quick run to get something from a shop (quick = 2 min to 15 and even 30 min sometimes!). Its usually neutral with handbrake on if the wait is more than 5/10 sec.

I've heard there's some effect of long periods of idling on the turbo. Would be grateful if someone can explain.

mgh · 22nd January 2012, 12:23

You also need to consider the status of your battery. Starting poses a load on the battery. During the night, the lights consume a lot of battery power. Unless the battery is less than a year old, I would hesitate to switch the engine off at night. Don't want to struggle to start the car.
Even in day time, with an old battery, I would not switch off the car.

If you want to stop the engine at signals, especially at night, pl. make sure your battery is in excellent condition (as good as new).

pranavt · 22nd January 2012, 12:58

If your car cannot charge the battery enough to restart an engine already at running temperature, you have bigger problems than having to worry about saving a few drops of fuel. Or you seem to have misconceptions about batteries and how they work.

ramzsys · 22nd January 2012, 13:11

What to do when traffic inches forward in a red light? One have to keep running the engine in such conditions.

libranof1987 · 22nd January 2012, 13:40

30 seconds or above and a/c is not required; that's when I turn off the engine.

Quote:

Originally Posted by PM - B

As has been shared by "null" above, it can take another 10 - 15 seconds for your turn to move once the signal has turned to green.

But do note that that 10-15 seconds delay is often because a LOT of people start their engines only when the car in front of them starts moving.

It is a good idea to crank the engine the moment the signal turns green; if everyone started saving those 10 seconds worth of fuel until it was time for them to move, the jams at intersections would clear much slower.

Quote:

I have noticed that when i do not shut the engine off at the traffic lights at Bangalore, i have got 14 - 14.5 KM/L efficiency.
When i shut the engine off at the traffic lights, i have consistently been able to get atleast 17 KM / L.

A difference of almost 2.5 kmpl?! I'm not really convinced by that logic. Agreed, the habit of not wasting fuel at intersections will result in better FE but not THAT much!

highway_star · 22nd January 2012, 13:54

Looking up articles on fuel saving tips, I have seen that the recommended time period beyond which you should not idle the engine ranges from 30 seconds to 2 minutes.

This should depend on the type of vehicle. I have worked out a rough calculation to estimate this time period. I am not an automobile engineer. Please correct me if I have missed something here.

The fuel consumed by an engine should be a function of three factors:
1. Quantity of fuel injected per engine cycle
2. RPM
3. Time for which the engine runs

The product of these three factors will give us the total fuel consumption.

If we have the data, we can calculate fuel consumed during starting. Then we can calculate the time period of idling which consumes the same amount of fuel. Idling beyond this time period would be wasteful.

In the absence of data, I will make some assumptions here:
1. Fuel injected per cycle during start up is 2 times that of idling
2. RPM during start up is 3 times that of idling
3. Time taken to start is 2 seconds

These are my guesses. I think assumptions 2 and 3 would not be far from the mark. Assumption 1 is a wild guess.

Multiplying the first two factors, fuel consumed per second during starting would be 2*3=6 times that during idling. If starting takes 2 seconds, it will consume fuel equivalent to 6*2=12 seconds of idling. So we should not idle for more than 12 seconds.

I would appreciate some inputs to refine the above calculation.

My practice is to switch off the engine if I expect a halt of more than 20-30 seconds.

PM - B · 22nd January 2012, 18:26

@libranof1987

Amazing isnt it, so hard to believe, but for my driving pattern, this is the difference i see. 2.5 KMPL. If i do not switch of the engine at signals longer than 30 - 40 seconds.

I drive mainly in Bangalore city from 8.30 AM to 9.30 PM. You may or may not have observed that Bangalore city roads have the highest # of signals per KM of road.

So it will depend on your driving patterns and city, but make no mistake, you will see a substantial difference, which in my case is 2.5KMPL.

@highway_star has given an approach to the logic also.

On the other hand, waiting 10 - 15 seconds is an indicator and am ready to move the movement the ride in front of me rolls.
So no worries on holding up traffic.

21st January 2012, 23:34	#46
null BHPian Join Date: Aug 2007 Location: Paradise (wish it was) Posts: 455 Thanked: 371 Times	Re: How long a break at signal deserves engine to be switched off Depends how deep your pockets are Getting back to the topic - I remember reading somewhere that every 5 mins of idling is equivalent to about 1 km of running a vehicle and hence it makes sense to shut down if >1 min. I switch off the engine even if it is 30 sec to go if there is a huge traffic pile up ahead of me. Usually it takes another 10-15 sec for me to move and hence it is still OK. But I have felt it is not that easy with a diesel car and usually I don't take a chance when I drive my friend's diesel. But then, it probably is so because I am not used to it.
	() Thanks

22nd January 2012, 00:09	#47
AbhiJ Senior - BHPian Join Date: Jun 2008 Location: Kolkata Posts: 1,498 Thanked: 1,257 Times	Re: How long a break at signal deserves engine to be switched off I normally have a 60 second time limit. Over that.. I turn off the engine. Below that, keep it idling...
	() Thanks

22nd January 2012, 00:35	#48
PM - B BHPian Join Date: Sep 2009 Location: Bangalore Posts: 216 Thanked: 327 Times	Re: How long a break at signal deserves engine to be switched off It is approximately 3 minutes of idling = 1 KM of travel. According to the FORD Driving Classes For Life. Why are we asking this question? 1. Fuel Efficiency 2. Life / state of engine 1. We are wasting fuel if the engine is on and the car is stationary. Hence from the first point, shut of the engine, if the wait is more than 30 seconds. As has been shared by "null" above, it can take another 10 - 15 seconds for your turn to move once the signal has turned to green. If the signal does not have a countdown timer, look to see if you are at the very begining of the signal or pretty close to it. This most times will tell you that you will have at least 30 - 60 seconds of wait. In which event switch off. I have noticed that when i do not shut the engine off at the traffic lights at Bangalore, i have got 14 - 14.5 KM/L efficiency. When i shut the engine off at the traffic lights, i have consistently been able to get atleast 17 KM / L. A huge improvement in the FE. Either ways i do shut the engine off. 2. If we are looking at it from the life / state of the engine, There are two ways to look at it, i am sure the gurus can add on to each in detail a.This cannot be bad for modern cars, that is, the start stop function of the engine, think, the more expensive hybrid cars have auto start stop function which automatically would do the same. b. I have read car manuals that state, if you drive in stop and go traffic or less than ~ 10 - 15 KM s, this is considered as stressful for the engine. I assume they also mean this because the engine might not have reached the operating temperature at all OR conversely it causes the engine to heat very rapidly.
	() Thanks

22nd January 2012, 00:46	#49
speedsatya Senior - BHPian Join Date: May 2004 Location: bangalore/manga Posts: 3,167 Thanked: 741 Times View My Garage	Re: How long a break at signal deserves engine to be switched off Anything more than a minute and I switch off the engine completely ( Even the music system goes off )
	() Thanks

22nd January 2012, 01:51	#50
Rahulkool Senior - BHPian Join Date: Oct 2007 Location: Chennai Posts: 1,467 Thanked: 2,125 Times View My Garage	Re: How long a break at signal deserves engine to be switched off I never shut off the engine, IMO its not worth the trouble lol and in chennai AC is also essential.
	() Thanks

22nd January 2012, 05:39	#52
mayankjha1806 Senior - BHPian Join Date: Jan 2011 Location: Bangalore Posts: 2,159 Thanked: 989 Times View My Garage	Re: How long a break at signal deserves engine to be switched off How does the whole equation changes if the car is a Diesel one. Unfortunately both my cars are petrol ones and i usually shut the engine off if i see timing anywhere above 30s. If i have to keep it on for various reasons then i put the car in neutral/handbrake and then wait for the signal to turn green again. I dont think one should stop in a gear and keep the clutch pressed while waiting (When engine is running). If its day time and hot i usually switch the AC on much before the signal so as when i am at the signal the car is cold already hence no problem for passengers if the AC is switched off for ~a minute.
	() Thanks

22nd January 2012, 07:25	#53
Nagesh BHPian Join Date: Sep 2006 Location: Bangalore Posts: 41 Thanked: 21 Times	Re: How long a break at signal deserves engine to be switched off Just to add to how we can judge when there is no indicator at a traffic signal, since i drive along the same route for the daily commute, we can anticipate "our turn" based on which side is passing. Ofcourse if we are way too behind, its a little difficult
	() Thanks

22nd January 2012, 08:15	#54
dingolphie BHPian Join Date: Dec 2011 Location: Kochi Posts: 123 Thanked: 201 Times	Re: How long a break at signal deserves engine to be switched off I'm sorry to say that I'm one of the guys that never switch off, unless it really is a long wait (cars are stuck). In fact I usually idle with a/c when my wife does a quick run to get something from a shop (quick = 2 min to 15 and even 30 min sometimes!). Its usually neutral with handbrake on if the wait is more than 5/10 sec. I've heard there's some effect of long periods of idling on the turbo. Would be grateful if someone can explain. Last edited by dingolphie : 22nd January 2012 at 08:16.
	() Thanks

22nd January 2012, 12:23	#55
mgh BHPian Join Date: Jun 2010 Location: Bangalore Posts: 396 Thanked: 40 Times	Re: How long a break at signal deserves engine to be switched off You also need to consider the status of your battery. Starting poses a load on the battery. During the night, the lights consume a lot of battery power. Unless the battery is less than a year old, I would hesitate to switch the engine off at night. Don't want to struggle to start the car. Even in day time, with an old battery, I would not switch off the car. If you want to stop the engine at signals, especially at night, pl. make sure your battery is in excellent condition (as good as new).
	() Thanks

22nd January 2012, 12:58	#56
pranavt BANNED Join Date: May 2008 Location: Mumbai Posts: 1,704 Thanked: 852 Times View My Garage	Re: How long a break at signal deserves engine to be switched off If your car cannot charge the battery enough to restart an engine already at running temperature, you have bigger problems than having to worry about saving a few drops of fuel. Or you seem to have misconceptions about batteries and how they work.
	() Thanks

22nd January 2012, 13:11	#57
ramzsys Senior - BHPian Join Date: Dec 2006 Location: NH209 Posts: 1,785 Thanked: 1,467 Times	Re: How long a break at signal deserves engine to be switched off What to do when traffic inches forward in a red light? One have to keep running the engine in such conditions.
	() Thanks

22nd January 2012, 13:54	#59
highway_star BHPian Join Date: Dec 2011 Location: Mumbai Posts: 121 Thanked: 128 Times	Re: How long a break at signal deserves engine to be switched off Looking up articles on fuel saving tips, I have seen that the recommended time period beyond which you should not idle the engine ranges from 30 seconds to 2 minutes. This should depend on the type of vehicle. I have worked out a rough calculation to estimate this time period. I am not an automobile engineer. Please correct me if I have missed something here. The fuel consumed by an engine should be a function of three factors: 1. Quantity of fuel injected per engine cycle 2. RPM 3. Time for which the engine runs The product of these three factors will give us the total fuel consumption. If we have the data, we can calculate fuel consumed during starting. Then we can calculate the time period of idling which consumes the same amount of fuel. Idling beyond this time period would be wasteful. In the absence of data, I will make some assumptions here: 1. Fuel injected per cycle during start up is 2 times that of idling 2. RPM during start up is 3 times that of idling 3. Time taken to start is 2 seconds These are my guesses. I think assumptions 2 and 3 would not be far from the mark. Assumption 1 is a wild guess. Multiplying the first two factors, fuel consumed per second during starting would be 23=6 times that during idling. If starting takes 2 seconds, it will consume fuel equivalent to 62=12 seconds of idling. So we should not idle for more than 12 seconds. I would appreciate some inputs to refine the above calculation. My practice is to switch off the engine if I expect a halt of more than 20-30 seconds.
	() Thanks

22nd January 2012, 18:26	#60
PM - B BHPian Join Date: Sep 2009 Location: Bangalore Posts: 216 Thanked: 327 Times	re: Switching off the engine at traffic lights @libranof1987 Amazing isnt it, so hard to believe, but for my driving pattern, this is the difference i see. 2.5 KMPL. If i do not switch of the engine at signals longer than 30 - 40 seconds. I drive mainly in Bangalore city from 8.30 AM to 9.30 PM. You may or may not have observed that Bangalore city roads have the highest # of signals per KM of road. So it will depend on your driving patterns and city, but make no mistake, you will see a substantial difference, which in my case is 2.5KMPL. @highway_star has given an approach to the logic also. On the other hand, waiting 10 - 15 seconds is an indicator and am ready to move the movement the ride in front of me rolls. So no worries on holding up traffic.
	() Thanks