Pros and Cons of Daytime Running Lights (DRLs)

A Fair and Balanced View of Daytime Running Lights

Last Update: 13 February 2004

NHTSA Report--DRL's are Ineffective!

Until I purchased a vehicle with DRLs, in January 2001, I thought that DRLs were the greatest thing since sliced bread. I would shake my head in knowing bewilderment whenever I read a Usenet post from some idiot who wanted to disconnect their DRLs. I tried to find a way to add DRLs to my older 1997 Honda CR-V by trying to find out how Canadian CR-Vs were wired. After all, what could possible be bad about such a wonderful safety feature that prevents millions (or is it billions) of accidents each year? How could the Volvo-driving yuppie scum be wrong?

Why all the Lies?
Money. DRLs are a feature that costs little to add to a vehicle. By intentionally incorrectly extrapolating data from inapplicable studies, companies like General Motors (and others) have created a problem that doesnít exist, and a solution to fix the non-existent problem. The problem for normal people is that the automaker's solutions are so poor that they make the problem worse or create a new problem altogether.

They could have done a DRL implementation that was good, but that would have cost more money. The important thing is that they can now advertise that their vehicles include this vital new safety feature. There are enough dumb people in the world to jump on the bandwagon of anything that, on the surface, appears to make driving safer. A similar situation exists with the lowering of the alcohol blood level for drunk driving. States are in competition with each other to see who can go lower. 0.08% is a good standard, the 0.1% was a bit lax. But now some states want to lower it to 0.04%. They have let hysteria impair their judgment and they want to go after people who are not impaired drivers. Then you get web sites, such as Woman Motorist, whose editors know little about automobiles and just want to sell web advertising (and who receives funding from, surprise, GM (see, jumping on bandwagons without doing any of their own research first.

Whatís bad about DRLs?
1. You lose critical traffic signaling methods. Flashing your headlights is
          a) the accepted signal to a trucker that it is safe to change lanes
          b) a signal to alert drivers that have forgotten to turn on their headlights
          c) a signal at a 4-way stop or in a parking lot to let the other driver go first
          d) a signal to other vehicles that you are traveling with that you need to stop.

2.You can't turn off your lights when
          a) they are glaring into another vehicle
          b) they are shining into a house at the end of a cul-de-sac or tee intersection
          c) they are shining at a pedestrian.
          d) You are sitting with the engine running on the side of the road, in someone's driveway, etc.
          e) you want to be able to see outside your side windows.

3. There are places where you need to drive with only your parking lights, i.e. drive-in movie parking lots, astronomical gatherings, military bases, etc.

4. Drivers with DRLs often forget to turn on their low beam headlights in rain or fog and at dusk or dawn. This is especially dangerous because the taillights do not come on until the low beams are turned on. Many drivers believe that in rain or fog the DRLs are sufficient and fail to turn on their low beams to activate their tail lights. When it is dark, the lack of dashboard lights is an indicator that the low beams and tail lights are not on, but in daytime conditions where the low beams should be used there is no indication that the DRLs, not the lowbeams, are on.

5. They make your bulbs wear out a little faster; not a big deal if they really provided a safety advantage.

6. They decrease your gas mileage slightly. See: The decrease in mileage due to the increased load on the alternator is very small, but it is still measurable. One one of the biggest proponents of DRLs, GM, asked for and received permission to disconnect DRLs when doing tests for their fuel economy ratings.

7. They annoy other drivers. This is a biggie. ďIn 1998, after receiving hundreds of complaints, NHTSA acknowledged that the intensity limits were too high and proposed reductions in DRL intensity. NHTSA cited a study by Kirkpatrick, et. al. (1989), that said that at 2000cd, the glare from DRLs was rated at no worse than "just unacceptable" in 80% of the responses. At 4000cd, the glare was rated no worse than "disturbing" in 80% of the responses. These subjective ratings are based on the DeBoer scale. Corresponding to these ratings, they found that at 4000cd the probability that the rearview mirror would be dimmed was about 70%. At 2000cd the dimming probability was 40%. At 1000cd, the dimming probability dropped to 10%.ĒThe NHTSA has now proposed that the European standard for DRL brightness be adopted. Expect the automakers to oppose this since it would add cost to do DRLs properly.

8. The people in favor of DRLs are so dimwitted and have such weak positions that DRLs must really be bad. Yeah, no one should be against something just because some really stupid people are in favor of it, but doesn't it make you uneasy to support something when someone else is supporting the same thing based on inaccurate and misleading "data?" In California, the way the majority of voters determine how to vote on ballot measures is by looking at the groups and people that support and/or oppose the measure, because it's very difficult for a layman to figure out what the ballot measure really means when each side is claiming that it will be better for the children if it passes or fails.

Woman Motorist magazine succumbed to the faulty logic and misleading statements of the DRL proponents, but at least they state their misinformed position politely, and they are funded by General Motors, so their position is understandable.

For a not so polite, but quite amusing and fact-free website on DRLs, click over to: The individual that did this site clearly lacks the logic that he claims to be promoting. He has many outright errors on his site, including his statement that DRLs usually use high beams and usually operate at 50% intensity, but the convoluted logic in some of his statements and examples left me rolling on the floor laughing. Don't they teach logic and the language of argument in Canada? At one point he blames the lack of DRLs for the death of someone who was hit by a stolen car that had no lights on?! What really is incredible is that his site claims to be "the home of logical driving," but the guy is a prime example of the people you see on the road that don't have a single ounce of common sense. I looked at some of the other pages on his web site as well. He has a lot to say, not much of it politely, but much of it very dangerous and illegal. For example, he favors blocking the fast lane of freeway traffic, because in his view people shouldn't be speeding. I hate tailgaters as much as the next guy, but the solution to the problem is to drive in the proper lane; there will always be someone that wants to go faster than you. Some of the strangest stuff on this site is where he tries to equate when a person pays their bills to how they drive.

Some False Arguments Used By Pro-DRL People

After the NHTSA published their findings that DRLs did not increase highway safety, and published the number of complaints they received regarding glare from poorly designed DRLs, some pro-DRL people went into a panic, and began creating incredible fabrications regarding DRLs.

Now let me say up front that I understand how some people are easily misled by major corporations (i.e. GM) and politicians, especially when presented with faulty research that appears to be legitimate. Furthermore, many people fall for anything that purports to increase safety or security, that claims to save lives, prevent accidents, improve their sex lives, etc. What drives me crazy is when people fail to use logical thinking and arguments to support their views. This invariably signals that they have no idea what they're talking about. For example, one webmaster wrote:

"How they (DRLs) would INCREASE highway hazards, I'd LOVE to know."

Well of course the answer was already well known, it's the glare caused by improperly designed DRLs. Of course not all DRLs are improperly designed, but GM has a particularly poor implementations, and GM is one of the major U.S. vehicle manufacturers.

This same person goes into a long diatribe about foggy windows, and vehicles without rear window defrosters. He dismisses the findings of the NHTSA, but of course he has absolutely no evidence to the contrary. He keeps stating how his personal experiences contradict all the evidence. He goes on to lie about the brightness of DRLs in the U.S..

It's sad that the people who are so pro-DRL feel the necessity to lie, are unable to engage in critical thinking, and are unable to look at the big picture. They are simply so convinced that they are right, and everyone else is wrong, that they have closed their eyes to the facts. The funny thing is, that I'm not even against DRLs per se, I think that they would be great if they were done properly.

Aside: I took a class in college where the text was The Language of Argument. It was not part of my major, but it was a valuable class because it explained how to see through all the false arguments put forth by people with specific agendas. Reading some of the pro-DRL web sites, I have a lot of fun picking out the false arguments. Twenty-five years later this book is still being used to teach the subject of argument, and is in its tenth edition. Click the picture below to purchase this book from Amazon. Alas, it's a textbook so it's quite expensive, but there are a lot of used copies around.

Whatís good about DRLs?
1. They are proven to reduce head-on collisions on two lane roads, especially at dawn and dusk. This is what they were designed to do, and if they were implemented just to do this then you wouldn't see much opposition to them. You often see signs on roads in California proclaiming "Daylight Safety Test Section -- Turn on Headlights." These are the places where DRLs would be useful. Sadly, instead of coming up with a way to use DRLs only when appropriate, certain parties would like them to be on all the time. Why? Money. It's cheaper to implement a lame system than a well-designed system.

2. They counteract the lack of common sense of dimwitted drivers that fail to turn on their headlights when itís foggy, rainy, or dark. Of course this is only a positive because these drivers are not doing the proper thing and turning on their headlights AND taillights. If the presence of DRLs causes drivers, who would normally turn on their regular lights in these conditions, to not turn on their regular lights, then this is a negative. A better solution to this problem would be sensors that trigger a warning to the driver to turn on their lights.

3. Some of the cars bought by the worst drivers come with DRLs, i.e. Saturns and Volvos. Thus the presence of a DRL equipped vehicle is a warning to other drivers to be careful.

Where the Logic of the Pro-DRL People Falls Apart
The proponents of DRLs are fond of pointing to examples of how DRLs help improve visibility in conditions where a competent driver would be turning on their lights anyway. The statistics show that the incidence of accidents caused by people not turning on their lights when they should, versus the accidents caused by the problems with DRLs, are about equal, at least in the United States. In short, don't use incompetence on the part of some drivers as an excuse to justify DRLs. There are other ways to solve the problem of incompetence. For example, in Florida, it's the law that you must turn on your headlights in the rain or fog, and drivers are conditioned to do this; in California there is no such law and many drivers don't understand that they should turn on their lights in these conditions (there is a bill pending in California that would require this).

Is there any proof that DRLs in the United States reduce accidents?
No. Read the report at: Look at the conclusions on page 24

How to solve the problems of DRLs?
DRLs have benefits when done right. Many of the opponents of DRLs came to their position only after they experienced poorly designed DRLs on their own vehicle, or were blinded by the glare of improperly designed DRLs. Properly designed DRLs, as are used in some European countries, would not generate as much passion.

If it were possible to disable DRLs, temporarily, when necessary, if they weren't too bright, and if they turned off momentarily (and automatically) when you wanted to use your headlights as a signal, then you would not see so much opposition. I have seen the problem of not seeing oncoming traffic on two lane roads, the problem DRLs were originally designed to solve, and the fact that DRLs reduce pedestrian deaths is an unanticipated benefit.

The problems with DRLs could be easily solved in several ways. Some of these methods are already in use, but not by all manufacturers, because of cost concerns.

1. An override switch that allows them to be turned off until the next time the car is started (or they can be re-enabled while the car is running) and that can be held in during starting to keep them off. I like this method because the default is still that the DRLs come on every time you start the car and you have to consciously turn them off. To implement this circuit you must know where the connection to disable the DRLs is, then you insert the relay contacts into that that circuit as shown below. I now add this circuit at the same time I install car alarm's in people's cars with DRLs (if they want this feature, and most do). It'd be great if a car alarm manufacturer would add a circuit like this to their high end alarms (it would just require two more GPIOs and a little programming and another optional relay).

If you're really ambitious you can make a little one-sided printed circuit board. I haven't tried it yet, but the layout could be as shown below (not to scale):

2. Turning them off when the parking lights are turned on (some vehicles work this way already), the circuit above implements this fix on vehicles without this feature.

3. Reducing the brightness (the NHTSA has recommended this). Unfortunately there is usually no simple way to do this on existing DRL set-ups.

4. Have the DRLs turn off for a couple of seconds when you flash your lights as a signal (this wouldnít be necessary if the DRLs were not so bright). This could be added and I am working on a circuit to do it (it was not as trivial as I originally thought).

5. Add sensors that trigger warning lights or buzzers when visibility drops due to rain, fog, or darkness, so drivers don't rely on DRLs (which don't turn on the taillights) in conditions for which they were not intended.

This ainít rocket science here, itís a trivial amount of circuitry much of which already exists in the vehicles ECU and it could be programmed into the system at no additional cost (software is free, right?). A couple of switches might be needed, but there may be some spare GPIOs on the ECU for the inputs.

Disabling Your DRLs
Due to all the problems with DRLs, most vehicle makers have issued bulletins to their dealers that detail how to disable Daytime Running Lights (DRLs). Try a Google or Copernic search to locate instructions for your vehicle(s). If worse comes to worse you can go to your dealer and pay them to disconnect them (just use the military base excuse). Consider adding the circuit I included above to gain the positive things about DRLs without being subjected to the negative things.

All of these methods were either sent to me or done by me. No guarantees!

Chevrolet S10

'99 Chevrolet/GMC Yukon, Tahoe, Silverado
Find the DRL Module. It's the grey box with a flip type bottom next to the white connector under the dash. If opened there is a circuit card inside. Leave the card alone. Find the PINK wire to the module. This is the ignition on detect wire. Clip this wire. That's it. No nore DRL. Everything else still works. GM puts a SPST switch in this wire as part of their Police Package (DRL/Radio Cutout Switch) to disable the DRL. I put a switch back in it so the DRL can be turned back on.

Pontiac Grand Prix




Note: On the 2001 4Runner the DRL relay is inside the vehicle, near the driver's right leg, just left of the center console. It is labeled "Running Lights." You can reach it without taking apart the dash at all; just reach behind it and unplug the connector, remove pin 2, tape it securely out of the way, and plug the connector back in.


There is a screwdriver hole next to headlight switch on some models (i.e. V70XC)

Other links: This organization actually goes a bit too far, in my opinion. While there arguments against DRLs are generally sound, what they should be working towards is a way to solve the problems of DRLs, rather than trying to eliminate them entirely.

DRLs, as currently implemented on cars sold in the U.S., have severe problems. These problems have been acknowledged by experts such as the NHTSA. Until these problems are corrected, either by legislation or by the automakers, the prudent thing to do is to disable your DRLs, if possible. Above all, you should research the facts about DRLs.

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