View Full Version : Idle Time


Oxygen
04-27-07, 03:45 PM
I have Fridays off, and people-watching is one of my bored-out-of-my-skull activities. Last week I was watching a supermarket parking lot and noticed something that got me to wondering about how it effects the air quality.

It's my understanding that an engine runs more efficiently under normal acceleration than at idle, assuming the engine is running fine, doesn't need a tune-up, etc. With that in mind, I watched people as they got into their cars, just to observe what "rituals" they go through before leaving their parking slots. Most loaded their groceries into their vehicles, got in, started the car, pulled on the seat belt, and left. Some reveresed the start/seatbelt order. But about a quarter to a third would get in, start the car, rummage through a purse or something, adjust the mirrors, mess with the stereo, preen and primp, then pull on the seat belt, adjust their appearance or position a little more, put the car into gear, mess with something else, then finally back out (or an equal amount of activity with the car idling, often in gear).

All the while, the car is sitting there idling. Aside from what it's costing in fuel usage and engine wear (as no cool air flowing under the hood), what's all this activity while the car is idling doing to the air quality? Add into this that there's probably someone waiting for the other driver to back out, so now he's sitting there, idling.

Do you think there's any significant impact, or is it too small to measure?

(This was one Friday in one parking lot. I imagine this goes on in every parking lot of appreciable size, seven days a week. And yes, you guessed it, the biggest indulgers in pre-backing-out activity were women. I'd say Hispanic women, but there's a sizeable Hispanic population here, so it only stands to reason that I would observe so many of them. As to the delayers being largely women, althoug it's mostly women doing the shopping, there are other shops in the same parking lot that are guy-oriented, such as car parts, a small hardware store, etc. That pretty much evened out the genders.)

draqon
04-27-07, 04:01 PM
Carbon monoxide
Nitrogen oxides
Hydrocarbons

Total # of vehicles in world: 1,000,000,000

(http://hypertextbook.com/facts/2001/MarinaStasenko.shtml)

Assuming each car releases 120 g of CO2/km and assuming that idle stage is the same as regular driving. (http://www.ncsc.ncsu.edu/news/news_story.cfm?ID=240)

(1,000,000,000) cars * (120 g of CO2/km) = 120,000,000 CO2 grams / km of all cars....assuming all of these are in idle stage for just 1km.... and really thats just the CO2...

spidergoat
04-27-07, 04:05 PM
That's why some cars like the Prius shut off when stopped. I think most people run their engines for a little bit before driving because it warms it up, which makes the engine last longer. It also powers the AC, and parked cars usually get hot. The engine doesn't need cooling until it heats up past a certain point. Also, measuring the efficiency of an engine when idling is comparing apples to oranges, it isn't doing significant work, but it is using the least amount of fuel compared to an engine under load.