Was wondering if I could garner a little help from you math whizzes and general smarties over here at the environmental forum. I am looking to put a dollar amount on what an average person wastes in gas everyday driving like most people drive. I realize to do this we will probably have to make a lot of assumptions, guesstimates, and averages. But I'm ok with that if you are. Obviously there are a lot of variables of why/how people drive inefficiently, but I'd like to focus on a big one: speeding up to a red light only to pretty much slam on the brakes. So focusing on this only and using a ton of averages of what type of car people drive, cost of gas, average distance driven per day, and probably others, I would love to know what someone could save daily just by trying to time lights and not speeding up to them. Any and all help would be much obliged. Thanks!
Go to fuelly and look at all the data there. You can categorize it by car models and years because we all know that certain makes and models of cars tend to have more wasteful drivers. Fuelly drivers tend to be more conservative, so you know that you would be a bit generous with your assumptions based on the amounts there.
One has to define "waste". Is single vehicle commuting waste? Is single vehicle commuting in a F350 waste? Is driving the vehicle you have even though it uses less fuel, but it's life cycle cost is already paid waste? Is driving anything other than the most fuel efficient (in the net/net) waste? Is driving instead of riding a bike, or walking or taking public transport waste? Complicated question(s). Icarus
I get what you are saying but I was thinking along the lines of what I laid out in pretty good detail.
1) Do you know anyone (family, close friend, interested co-worker) who has a car split between two drivers of very different driving styles? I you can convince the "caring" driver to record the mpg's between the two drivers it would be a start point. 2) Use the Prius. On one tank of gas, coverup the mpg display and drive like everyone else (but still stay safe, just inefficient). The percentage difference in mpg would be interesting to everyone here.
If you are in a car without regenerative braking and you accelerate to the same speed between stops, then the same amount of energy, your kinnetic energy will be used in stopping. This is 1/2 x weight of the car x velocity squared. On some cars the fast starts are less efficient, but this difference should be small. The key factor will then be fuel wasted idling since you are stopped longer. Still unless you have many lights this will not be a huge factor. Now is you do time the lights, you are likely doing something quite different. You won't accelerate to the same speed, and since this is squared you are much better off, you also won't lose all the kinnetic energy when slowing down. If you want you can plug numbers into the equation, and use 33.7 kwh to 1 gallon of gasoline and something around 25% efficiency to accelerate fast in a car with an ordinary ice. Turbo charged cars with rapid acceleration have a greater efficiency penalty. In our hybrids we don't have the idling losses, so as long as we don't get out of the efficient range of the engine, acceleration doesn't matter. Deceleration though matters a great deal, as if we do that slowly we can reuse the that energy. Again the key is speed that you accelerate to from the light, as well as slowest you need to go.
1/2 * 1590 kg * 13.4^2 = 143 kJ = .04 kWh Does this look about right? This is using about a 3500 lb vehicle going from 30 mph to 0. Did I do that right?
This assume Tht you can recapture 100% of the potential energy upon deceleration. In fact you can't, and in the al world you can't come close, if for no other reason that once the battery becomes fully charged, there is no place to "put" the recaptured energy. Icarus
I think so, I didn't check the math, but it looks right. That gives the energy lost in braking. I don't know how efficient the ice is at accelerating up to that speed, but if its 25%, then you would have used (.04kwh)/25%=0.16 kwh worth of gas to get to that speed. If you were at 15 mph when you needed to hit the brakes you only would have wasted 1/4 of that gas. There is the additional gas of idling. If you don't have to brake you don't really waste it. I have no idea what speeds and the number of stops people go through. He was calculating waste. If you don't need to brake, or brake from slower speeds, you don't waste that energy. The trick is not to have that kinetic energy in the car when you hit the brakes, by timing the lights. This is often easier said than done, but by not racing to the lights energy can be saved.
