[xyzzy_plugh]

I just always turn my headlights on when I start my car. It doesn't matter if it's day or night, or it'll get dark while I'm driving, or if it starts raining or I go through a tunnel. The lights are just always on.

If everyone's car just did this automatically, the world would be a safer place. Why would you ever want the lights off?

[gambiting]

Well, ask in countries which actually have that as law - Poland introduced it few years ago and the jury is still out on whether it made roads safer or not. I'd argue it didn't - mostly because as a driver your brain starts to associate lights = moving car. Which means that you start to ignore everything that doesn't have lights - bicycles, cars where someone forgot to turn the lights on. There were studies done on this and it's very inconclusive that it improves safety at all.

[icc97]

Given it's a safety feature the main reason not to do it would be if somehow it made things worse. Even if the effect is almost negligible you're still going to save a couple of lives per year.

Once LED lights are more standard and there's less issue of replacing bulbs or wasting electricity it seems a no brainer.

[gambiting]

Well, that's the whole separate point in this discussion - normal headlamp bulbs are 60W - so you are using 120W of power to run two of them. How many cars are on the road for a country the size of Poland at a busy time of the day? 100k cars? That's 12 megawatts of power being used every day just to run some lights - and that's not counting rear lights at all. Generating 12 megawatts of power using thousands of ICEs is a massive waste of fuel, and it's probably incredibly hard to prove that conclusively, but I wouldn't be surprised if burning that fuel caused more deaths overall than having the lights on saves. I don't know if we can find any studies that would say either way though. Automotive LEDs are still within 10-15W range each, so while better than halogens they are not free.

And finally, I think there was a Polish study that said that yeah, while with the lights on you are more likely to notice a car, you are less likely to notice a cyclist - and hitting the latter has much worse consequences than hitting the former. So it might have made things worse.

[dsfyu404ed]

Headlights and DRLs are not the same.

Most OEMs just make the headlights (and the headlights only, not the tail lights) always on in markets where DRLs are mandatory. The latter is what you get when you do what Canada did and require DRLs and don't require them to also be poor at being headlights.

Pretty much any time when you want to signal the intention of not going anywhere is a darn good time to have your headlights off. Cars actually have parking lights for exactly this reason. They also work great for creeping around your own driveway without throwing too much light on the windows of houses in the very early AM.