keeping lights off, how much fuel does it save really

[brucey]

What about efficiency loss?

[vacationtime247]

Dont' run with my lights on when I'm in a car or truck except when conditions require. But when on the motorcycle, they're always on. Always thought of DRL as a nuisance.
VT247

[Piwoslaw]

When Poland switched to mandatory lights 24h/year round I saw newspapers usually citing 2% as the increase in fuel consumption. I decided to install LED DRLs (2 x 5.5W = 11W) since in order to drive with my lights I'd not only have the headlights (2 x 55W), but also position lights, registration plate lights, dashboard lights, etc., plus all the relays that power those lights, which I figured totalled to ~200W. When the engine is warmed up I see instant fuel consumption at idle go from 0.50-0.53 l/h to 0.56-0.64 l/h when I turn the lights on.

As for whether DRLs increase safety I can say that yes, they do. First of all, on a sunny day (when many people think that DRLs don't help) some cars tend to blend into the pavement and/or horizon when far away. I can spot them much sooner if they have lights.

Second, among the many dumb games teenagers like to play is driving at full speed on the highway. Against traffic. At night. Without lights. If their car has DRLs which can't be turned off, then that increases the chances of any innocent drivers that might be unlucky enough to be on that stretch of highway.

[Fat Charlie]

Originally Posted by Piwoslaw

First of all... I can spot them much sooner if they have lights.

Second, among the many dumb games teenagers like to play is driving at full speed on the highway. Against traffic. At night. Without lights. If their car has DRLs which can't be turned off, then that increases the chances of any innocent drivers that might be unlucky enough to be on that stretch of highway.

I'm with you on the first, but making it more convenient to pass under some circumstances doesn't really make me want to require equipment across the board. Your second reason is a little out there- mandating equipment to make one part of a criminal activity a little less convenient just doesn't make sense to me. If the kids like doing it without lights then they're going to do it without lights no matter what you make everyone else buy.

[PaleMelanesian]

It makes a big difference if you EOC. It can make the difference between starting or not at the next red light. If you have to engine-ON-coast instead to keep the alternator running it costs you a lot more fuel. Something in the 20% range I'd guess.

[Piwoslaw]

Originally Posted by Fat Charlie

I'm with you on the first, but making it more convenient to pass under some circumstances doesn't really make me want to require equipment across the board. Your second reason is a little out there- mandating equipment to make one part of a criminal activity a little less convenient just doesn't make sense to me. If the kids like doing it without lights then they're going to do it without lights no matter what you make everyone else buy.

OK, I was half joking with the second reason

[Arragonis]

Originally Posted by PaleMelanesian

It makes a big difference if you EOC. It can make the difference between starting or not at the next red light. If you have to engine-ON-coast instead to keep the alternator running it costs you a lot more fuel. Something in the 20% range I'd guess.

If it was this much I would expect to see it on the GPH figure at idle and turning my lights on or off makes no difference that has stood out so far - I think I will experiment tomorrow morning...

[PaleMelanesian]

What's your idle gph? Mine's about 0.3. Compare that to the gph of EOC = 0. Now apply that difference to half of the drive that I EOC. It makes a big difference.

Estimated 0.3 * (0.5 hour drive * 1/2 (eoc percent)) = 0.075 gallons
Regular commute = 0.14 gallons (10.5 mi / 75 mpg)
0.14 + 0.075 = 0.215
10.5 / 0.215 = 48.8 mpg if I engine-on-coast instead. That's a 35% drop!

[Arragonis]

I forgot to check this morning as we were in a hurry. Just went out and idled for a bit and its on 0.25 which is higher than normal - probably because it has sat at work all morning and isn't warmed up. I shall check again later.

Normally it is under 0.2.

[dcb]

As I mentioned before, and it is the sort of thing I will probably have to mention again, since it is the sort of thing that is surrounded by a massive SEP field (Someone Elses Problem), but extraneous lights on cages in the daytime take attention away from pedestrian traffic and more pedestrians get hit as a result, is my current hypothesis to explain why DRLs result in more pedestrian deaths.

Here was what I came up with originally:

Originally Posted by dcb

thanks for that Blue,
so here is the dilemma:

We have a biased pro DRL page with actual and fairly recent studies indicating that more pedestrians are run over with DRLs on, 16 percent more. And a presumably less significant (and even more bizarre) stat from 30 years ago about slightly less people getting hit with two cars at once.

FYI, Worldwide, 2/3 of people killed in vehicle accidents are pedestrians. According to the AAA, http://www.aaafoundation.org/pdf/Saf...tureReport.pdf , 1.9 per 100,000 are pedestrians and 15.6 per 100,000 accidents are occupants.

So if the pro DRL data is to be believed then why does it seem like it is at the cost of more pedestrian lives? What the hell was going on in denmark in 1993? I absolutely do not like the idea of mowing down more cageless folks and cannot think of a conclusive reason why DRLs shouldn't be safer, but WTF?

I think we've settled on the 500 million gallons of gas annually figure for running all those DRLs.