Daytime headlights

I did a search for this topic, but didn’t see anything relevant. Google wasn’t much help either, turning up mostly irrelevant links with only a couple that mentioned the topic but did not actually explain anything.

The question is this: while driving in the mountainous desert north of Los Angeles, I once came upon a traffic sign I’d never seen before. It indicated that drivers were to turn on their headlights in the daytime, while traveling through a specified distance (something along the lines of “Daytime Headlights, Next 11 Miles,” but I forget the exact wording).

I’ve heard lots of talk about the merits of daytime running lights for cars, but it seems those advantages would apply anywhere, so why not just make a law about it and bag the signs? It seems to me there’s got to be something peculiar about that particular stretch of road. But, at least to me, there didn’t seem to be anything “special” about either the road, or the terrain surrounding it, other than that it was pretty isolated. I was thinking, since it was the desert, that maybe from time to time there was enough dust in the air to at least partially obscure an unilluminated vehicle, but surely drivers would notice that condition and again, the law could instruct accordingly. So my question is, simply, why?

Thanks in advance for your replies.

Well this isn’t an answer, but there was a stretch of highway in New Hampshire that had the same sign. It wasn’t a particularly hilly or curvy stretch of road, but it had lots of accidents, there was no divider in the road. This was in the days before “daytime running lights” existed. Presumably somebody thought the lights made your car more visible, but in my opinion it just created glare and was more of a hazard.

IIRC that stretch of road, and others, are the test roads for daytime running lights. They take different roads around the country and compare accident rates with and without daytime running lights. That’s how they develop the statistics that say things like “DRL mean a 46% reduction in accidents” or some such bull. Although personally, I think the signs are a Plot by the Men In The Black Helicopters. They monitor what percentage of people blindly follow directions on a sign around the country. When the total gets to a certain point, they know it’s time to unleash their takeover bid! You have been warned! Fight the System! Refuse to follow directions!


“Golly, officer, I didn’t mean to run into the car coming the other way, but I was looking down trying to find my headlight switch.”

The “Daytime Lights” roads are particularly dangerous sections of roadway. By asking everyone to turn on their lights the towns/states believe they can reduce the accident rate. I know the section in NH that ratatoskK talks about, and there’s one on Cape Cod as well.

There isn’t a law since that would take a while to pass over all 50 states. All cars now sold in Canada are required to have DRLs but there are lots of cars on the road from before it was law.

I’ve been trying to get myself in the habit of driving with lights on in the daytime, at least on two lane highways. In fact, I wouldn’t complain a bit if it was made a state law. It really does make your car much more visible to oncoming traffic, which is extremely important in passing situations on two lane highways, especially if one lane of traffic is blinded by the sun. Or if you’re driving through a deeply shaded forest, for that matter (or the worst–a mix of the two).

There’s a stretch of Route 2 in the eastern part of Franklin County, MA with the same DRL requirement. There have been some nasty accidents there, some apparently because people are stupid and don’t realize the road changes from a 4-lane divided highway to a 2-lane road at that point and drive on the wrong side of the road. It’s much easier to notice that mistake before it’s too late if everyone has their headlights on.

As an aside, it bugs the crap out of me when people drive with their high beams on in the daytime. Even though it’s light out it’s still painful to look directly at a car’s high beams!

Anecdotal evidence here: taking a shortcut through the (paved) backroads in central Mexico, I certainly felt safer with the headlights on. Lots of hills there, and Mexican truck drivers (in particular) and paisanos (in general) have no respect for unbroken lines (no passing) on the road. I guess they don’t understand that they can’t see over a friggin’ hill. Dangerous as hell, and there’s typically no place to pull over to when they’re barreling down on you.

The lights, at least, let them see that there’s someone heading their way before they can actually see you.

There is at least one state (a Carolina IIRC) where you must use your headlights if it is raining. The signs use the word “burn”…something along the lines of, “Burn headlights if using wipers”.

In NH, there are signs stating the requirement to have your headlights on if your windshield wipers are on.

You’ll see follow up signs after they tell you to turn them on that say:

“Turn of your headlights now, Dummy!”

In daytime driving when headlights are required, people leave their lights on at a rate that is incomprehenisble, and they wind up with dead batteries.

Whenever there is some cause to put headlights on, it becomes a mess. example: ‘Put your lights on for the troops = AAA and every garage in America is buried with callers needing jump starts.’

Quite a fiasco. Don’t ask drivers to to it everyday, but get cars built with it IF IT TRULY reduces accidents, but I don’t think there is evidence for that claim.

Here, too, but I don’t recall seeing any signs about it.

I guess they figure that when it rains you will have your wipers going, but I’ve applied some stuff to my windshield in the past that makes wipers unnecessary (Rain-X?). So, if it is raining and I use that product and I am not using my wipers I could get out of a ticket written for not having my headlights on. Right?

Unfortunately, even with the best of intentions, including any statistical information supporting daytime headlights, we will still have idiot drivers out there who fulfill the stereotype – “Lights on; no one home!”


Just to provide a bit of information about what effects daytime driving lights have. Here in Denmark it’s been law since 1990 and you can see a graph with accidents since 1970 here: - it’s a bit crude but accidents seem generally seem to have been declining since the beginning of the stats and it’s a bit hard to see if if the drop has anything to do with passing of the law. The comments about what happened in what year are in Danish however.

The largest drop actually seems to be around 1973 where speed limits where restricted due to oil shortage (they where raised again in '74).

If you want to pass some time there is a study on safety effects of daytime driving lights here: - it also has a lot of imformation about the resources used and costs when running lights 24/7.

The mountains, or the desert? Pearblossom Highway, east of Palmdale, has (or had) an 11 mile stretch where headlights are (or were) required.

As has been stated, the stretches are to gather data about whether using headlights reduces the number of accidents. At least, that’s what I’ve been told.

I had always thought that the signs were there for particular times during the year on longer straightaways. There’s Rt 32 which, during winter and springtime the sun shines directly in line with the road making so much glare it’s very hard to see on-coming traffic unless their lights are on making it easier to see them through the sun’s intense glare. Also on Rt. 90 in Ocean City, same thing with the same problem.

Are there a lot of tunnels on this road? On the Blue Ridge Parkway in the mountains of western North Carolina there are signs before each tunnel reminding drivers to turn on their headlights.

Other places in California that have daytime headlight rules that I know of are in Malibu Canyon and Highway 138 from Castaic out to Fillmore. The latter road has been widened so it’s a lot safer now.

I hope the places that tell you turn on your headlights going through the tunnels, also tell you to turn them off once you get out.

They do on the BRP. There is a sign after each tunnel saying “Check Lights” or something to that effect.