All this talk about whether or not to have a safety feature, based on the fuel cost of having that feature, makes me wonder: How much fuel could be saved by removing the seat belts? After all, seat belts and the associated hardware weigh several pounds. The weight reduction would surely help FE. How much fuel could be saved by removing the air bags? They have to weigh at least a few ounces each. How much weight is involved in the machinery for the anti-lock brake system? The tail lights and brake lights? I'm sure there are other safety features that could be removed, too. After all, if you never have a collision, all of those safety features are wasted.

Of course, I'm only kidding. Some of those things are actually required by law. And, after a bad collision a few years ago, I was really glad that my car had air bags and seat belts.

There is a whole profession called risk analysis. The idea is to consider the cost of a risk by multiplying the probability of an occurrence by the cost of an occurrence. For high-cost occurrences, like accidental death, it is worthwhile to spend significant money to avoid even an extremely small probability. For most occurrences, like property damage, you can calculate the expected cost both with and without the prevention, and then make an informed decision of whether to spend the money on prevention.

I put most auto safety items in the category of preventing accidental death. They reduce the probability of an occurrence of death. The amount of that risk reduction has been studied by insurance companies and governments, and found to be compelling. I don't have to personally experience an accidental-death event before I am willing to believe that the risk-reduction is worth the cost.

 

Not being an electrician or knowing much about electricity other than how to change light switches and install ceiling lights and fans I'm going to use a little laymans math here....

Sylvania H13 bulbs
Lumins: Low 1000 / High 1500 +/- 15%
Watts: Low 55W / High 65W

Headlights on: (2 X 55W) @ 12V
12V/1.3Oh/9.16A/110W (0.11kWh)

DRL ((2 X 55W) @ 12V)*0.5[running at 50% power]
6V/0.65Oh/9.16A/55W (0.055kWh)

Assumption based on above math: 0.11kWh = 0.9MPG
then
0.055kWh = 0.45MPG

Assuming 34MPG in a 2009 FEHL FWD
100,000 miles / 34MPG = 2941.176/gal
100,000 miles / 33.55MPG= 2980.626/gal
39.45 additional gallons over 100,000 miles or
0.547 gallons per month based on reaching 100,000 miles in 72 months (our average driving).


Same calculations based on Gary's 80% figure
Headlights on: (2 X 55W) @ 12V
12V/1.3Oh/9.16A/110W (0.11kWh)

DRL ((2 X 55W) @ 12V)*0.8[running at 80% power]
9.6V/1.02Oh/9.26A/88W (0.088kWh)

Assumption based on above math: 0.11kWh = 0.9MPG
then
0.088kWh = 0.72MPG

Assuming 34MPG in a 2009 FEHL FWD
100,000 miles / 34MPG = 2941.176/gal
100,000 miles / 33.28MPG= 3004.808/gal
63.63 additional gallons over 100,000 miles or
0.883 gallons per month based on reaching 100,000 miles in 72 months (our average driving).

NOTE: I have used the above calculations because I have interpreted the 50% power @ 50% duty cycle as achieving 50% power by cycling the resistor on and off at half the rate of normal, not sending 50% of the power 50% of the time.

That being said, its time for a fresh cup of coffee.

 

Just had mine (coffee).

I don't think the resistor would be cycled, it's all a bit above me - I do software, not electricity - but I think my original numbers were accurate. For one thing, having an AWD means lower mileage, which means more gas used over the 100K. You were working with FWD.

But I will grant you even the $70 or so over 100K miles, I still make the choice because I have seen for myself how much more visible the vehicle is to other traffic when they have DRL.

 

Oh, I'm definately going to have the DRL's turned on for my wife. I'm just having fun trying to figure out the numbers. Figure it out now, file it away in the back of my head and maybe one day it will be useful.

Also, as time and money permit. I will look for ways to offset the FE hit by reducing electrical load in other ways. Possibly by using LED lights like John(GPSman).

 

No gpsman1, I my mind is still in place (I hope!). I was simply using twolostminds' claim of 50% voltage for 50% of the time, to show what its consequences would be. I myself don't believe 1/8 power to be the case; it is almost certainly more than this. In my 1993 Camry, which was from the early days of required-DRLs in Canada, Toyota simply put the two high-beam bulbs in series for DRL operation. This means that each bulb had 1/2 the voltage, and so 1/4 the normal power usage. The brightness was okay for DRLs. So I would expect that around 1/4 the normal power usage would be closer to the truth. In my current TCH, the high-beam lamps are driven in parallel by a pulse-width modulated MOSFET switch, so that any power ratio, from full to zero, is in principle possible. I don't know what power ratio they actually use.

Stan

 

i replaced my bulbs with HID's, less wattage draw = more MPG? haha!

 

I forgot to give my 1.825 yen (2cents)

I'm going to get mine turned on once I get home!

 

Personally I have replaced the factory DRLs (a voltage dropping resistor and both high beams all in series) with 3W Luxeon LEDs on my 2001 RX300. I also upgraded to the Canadian DRL technique, tail/street/parking lights on also, also all converted to LED bulbs.

Maybe 10 watts total.