No Back Lights at Night? Blame Daytime Running Lights [DRL]

Daytime Running Lights [DRL] commonly only illuminate the front lights of a vehicle, and not the rear lights. (See the photograph below.)

Usually, they also do not illuminate the dashboard lights for the speedometer and other instruments and controls.  This is intended to alert drivers to the fact that only the DRLs are operating and therefore only the front lights are on, but as most drivers have never been adequately informed about this scenario, many just assume that there is a fault with the dashboard lights and drive on, unaware of the danger they are causing for themselves and others.

Photograph of a vehicle displaying frontal "Daytime Running Lights" (DRLs) but no rear lights -- a potentially very dangerous situation, especially in heavy rain or fog, where visibility is reduced.
A regrettably common sight in North America:  A vehicle running on Daytime Running Lights (DRLs), where the driver sees light at the front and assumes that all lights are on, but DRLs have less power than low-beam headlights and typically only operate the front lights and not the tail lights. This creates significant danger from behind, especially in heavy rain or foggy conditions that reduce visibility. Usually, the dashboard instruments are also unlit — and this is intended as a clue for the driver — but as drivers have not been adequately educated about many aspects of safe driving, many just drive on, oblivious to the danger they are causing. (Copyright image.)

DRLs were brought into use quite a few years ago because of concern from environmentalists that using “unnecessary,” additional electrical power in vehicles does fractionally increase fuel consumption and therefore it also increases pollution.  My response to this — as a person who has been an enthusiast conservationist and now environmentalist, for over 50 years — is the question:  “When does it become worthwhile to risk human lives for the sake of preventing undeniably miniscule amounts of pollution?”  There are many much more serious sources of pollution that would give far greater gains through their removal and create safer conditions rather than additional risk for people.  In every context, they would achieve more.

What are the benefits of driving with headlights on at all times?

Through targeted research, it has been shown that using low beam headlights or DRLs — at all times of day and no matter how good the weather and natural light are — increases the conspicuity of your vehicle and thereby reduces your chance of having a vehicle or a person emerge into your path and trigger a collision.  Depending on exactly how the results are measured, the reductions in risk vary between 14 percent and 28 percent.  As having a vehicle or Vulnerable Road User [VRU] come into the path of your vehicle is clearly a very dangerous type of collision, it is equally clear that even a slight reduction of the risk level is a very good thing, and a cut of 14-28% is actually a major issue.  So it is very wise indeed to drive with low-beam headlights or DRLs on at all times.

Indeed, in Sweden using headlights at all times of day, even in full sunshine, was recognized as giving important safety benefits as long ago as the late 1960s, and since then it has been the law there to do so.

To put this into further context, Sweden has long been one of the two most frequent leading nations in the world for having the lowest rates of road deaths (the other such country being Great Britain).  So it is fair to assume that they know what they are doing.

What are the automakers doing wrong?

The ridiculous scenario of cars using DRLs being driven at night with no rear lights on has been going on for years, and the situation is a dangerous disgrace.  (And even the majority of other drivers who see cars with no back lights on at night typically don’t know what the cause is… There’s that lack of adequate and accurate education again.)

The situation could be rectified in a heartbeat if car makers simply combined DRLs with the sensors used for “automatic headlights” (which come on only when it starts to get dark).  Doing this would mean that in good light only the front DRLs would illuminate, thereby saving that very small amount of extra emissions for which they were intended.  However, even this would require the sensors to identify poor light as opposed to imminent, proper darkness, because it’s the lack of rear lights during bad atmospheric visibility — such as heavy rain and spray, or fog, or falling snow, that is the most dangerous scenario which current DRLs typically fail to rectify.

What’s the safest thing for drivers to do?

The safest answer is extremely easy.  Simply turn on your proper headlights every time you get into the car, to drive.  Not DRLs, not automatic headlights — proper headlights, on low beam… at ALL times.

The conspicuity of your vehicle — again, at all times — is a major factor in your safety, so feel free to enhance it.

And those extra emissions?  You will have to work out for yourself whether the tiny additional amount involved, by switching from DRLs to low-beam headlamps in your own vehicle, are worth anything even remotely close to the value of your own life and/or the lives of any other people in your vicinity.

Young people might say that the decision is “simples!”


Author: EddieWren

Eddie Wren is the CEO and Chief Instructor at Advanced Drivers of North America. His driver safety background is given at:

11 thoughts on “No Back Lights at Night? Blame Daytime Running Lights [DRL]”

  1. never heard it was to save power. I do not understand why automatic headlights are not mandatory, there are so many things on cars now that are less important. What bugs me now is the led headlights that turn off the side that is using the turn signal even in the dark.

    1. Steve, thanks for your comment.

      My own concern with automatic headlights is that they, too, can fail to provide increased safety in conditions of bad visibility when ambient light levels are not sufficiently low enough to trigger the lights. This concern applies equally to both front and tail lights.

      Two other concerns arise from our respective comments. The first, as you rightly say, relates to headlights that switch off to allow a front turn indicator to be seen, which quite clearly is poor design. The second is in connection with conspicuity of vehicles from behind in thick fog (or smoke), heavy rain and spray, and heavily falling snow. I am referring to rear, high-intensity ref fog lights, a subject I wrote about at:

  2. As you point out, it would be so easy to fix; if the car is moving and the system says it’s dark, lights on automatically or at least a warning to the driver. Another way is to make DRLs not bright enough to illuminate the road at night, e.g. my personal vehicle has DRLs bright enough to be seen in daylight by others, but at night they don’t light anything beyond 3m/9ft.

    Both require manufacturer involment, but it’s a better solution (upstream) than training/education.

    Having said this, part of being a safe driver is making sure other road users are aware of you!!

    Keep up the good work!!

    1. Thanks for your kind comments, Fernando.

      My concern regarding low-powered DRLs is the fact that as front-light power decreases in daylight conditions, I suspect that the lights’ effectiveness in drawing attention to the approaching vehicle may decrease too. I would lean the other way and have low-beam headlights and the tail lights wired to come on at any time the vehicle is moving (and sidelights only usable when the vehicle is static — though that is the subject for another blog/article about people sitting parked at the roadside at night yet keeping their headlights on, thereby unnecessarily affecting other drivers’ view).

  3. Another great article Eddie. Unfortunately I am not surprised by the number of ghost cars on our roads after dark. I am however dismayed by the numerous drivers with burned out, non-functioning tail-lights; a definite education/enforcement issue. Have you ever examined the efficacy of rear fog lights, such as in Europe, and the compromise non-solution killed by politics in the USA?

    1. Thank you for your very kind comment, Jack.

      I agree entirely with your thoughts about driver negligence and failure to maintain their lights in clean, clear and fully-operative condition. In Britain, where I spent many years as a traffic patrol police officer (similar to U.S. state police and highway patrols) the law was very rigid. Anyone who was driving with one or more defective lights was asked: “When did you last check [the light/s in question]?” If their answer was anything other than an adequate version of “When I got into this car at the start of this journey,” they could and probably would end up in court. As a result, the goal was at least partially achieved and there tended to be quite few vehicles with defective lights!

  4. Also be aware that Chevrolet car maker have newly made some of their vehicle showing back up lights on when in park. Very much miss leading, so we do not know if the vehicle is ready to back up or just being parked, not saying anything else about Chevy the company that we all had to Halo to ba Bello to Bail out still not doing anything right ???

  5. Blaming the manufacturer or technology is simply a way to NOT take responsibility for pour actions. Daytime running lights were an idea, not turning on the regular lights at night is a choice from the driver.
    Let’s stop looking outside for blame and let’s start looking at ourselves and what we do (or don’t do).
    Every driver is responsible for the way they operate their vehicle, not the manufacturer or anyone else.

    1. Mr Fournier, while I agree wholeheartedly with the concept you are teaching at your company, I regret that you appear to be a long way behind when it comes to global road safety best practices.

      For many decades, the so-called “Three E’s” of road safety have included not only ‘Education’ — the field in which you and I work — but also ‘Enforcement’ (in the traffic aspect of which I used to work as a ‘Roads Police Officer’) and just as importantly, ‘Engineering’.

      It is not realistic nor fair or appropriate to blame drivers for all things that go wrong with road safety and the causation of crashes. The ability of DRLs to be on at night, thus illuminating the road ahead, while there is no actual, *tangible* warning to drivers that not all of their lights are on, is a serious omission by vehicle engineers, at whose feet at least part of the blame must lie.

      To make this point more telling, I would ask you to tell me how many vehicle/driver handbooks you have read in which it is prominently and clearly pointed out that the DRLs on the vehicle **do not illuminate the rear lights,** or that if the dashboard lights aren’t on, neither are the back lights. (Indeed, there are now some vehicles available in which the dash lights *are* on when just DRLs are in use, even though the back lights are not!)

      It is all well and good, implying that all drivers must be the epitome of absolute concentration when driving but in the real world we all know that will never and can never be the case. Research bodies have long since come to the conclusion that typically the driver is the weakest link in the chain and cannot be relied upon in the manner that you infer. None-the-less, you and I both DO know that motivated individuals can indeed be trained to concentrate, anticipate and avoid problems better than other drivers. Sadly, these individuals will always be the exception rather than the rule.

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