I have always wondered exactly what daytime running lights accomplish-except wasting energy.
Suppose we have 100 million cars, each with 2 5o watt headlamps, , running for 5-7 hurs per day. How many millions of barrels of oil is this wasting?
Before they were mandatory in Sweden there was a study run to define the increase in fuel use.
Unfortunately it was so long ago that I don’t recall the findings but it was relatively insignificant as far as I recall.
They make your vehicle more visible to other drivers. There have been studies conducted which show that as a result of this increased visibility, the number of accidents is reduced. This saves lives, reduces our overall insurance burden and generally makes roads safer places.
So, to answer your question, they don’t waste any energy at all.
The use of day time lights increases the visibility of the car, especially in low light or hazy conditions. This has been required (in most states) on motorcycles for decades, but only recently allowed on automobiles in the US (since circa 1995, IIRC). I haven’t seen any conclusive studies that demonstrate their effectiveness, but anecdotally I’ve noticed that under the aforementioned conditions cars with DRLs are considerably more visible than those without, and concerns about glare and turn signal masking are mostly a non-issue in sunlight.
The amount of wastage, in terms of gas mileage, depends on the implementation, but it varies from negligible (for low-power systems) to about 6%. This depends not only on the system (full power versus reduced output) but also the kind of driving that is typically done; for city driving with regular acceleration peaking the comparative loss is very low; for highway cruising on level ground, which only takes about 20-40 kW (for modern passenger cars) the difference between headlamps and no headlamps is higher. Headlamps range from about 35W to 85W (per bulb) in output, depending on type and size. A dedicated LED array would probably offer the same benefit of visibility (if there is one) and without glare but with lower energy use than illuminating headlamps, which are designed to see rather than be seen.
So the loss is non-negligible, but not huge, and with advances in HID efficiency and increased use of LEDs in auxiliary and supplemental lighting, will probably get better.
Stranger
Stranger
Well answered Q.E.D.!
I was too focussed on the actual increase in energy usage. That energy is indeed far from wasted.
I suspect those studies compared using DRLs to no lights at all. Comparing use of DRLs with use of parking lights instead, which also make your car more visible, but use less energy, the benefit might be much smaller.
I also suspect that, while the cars using DRLs benefit, cars with no lights on at all probably become harder to notice among the cars with DRLs, and thus more likely to be in an accident.
I’d wager the 5-7 hours per day estimate is a bit high. I imagine the average for all cars driven in a day is more like 1-2 hours.
On what basis? Other than confirmation bias, there’s no reason to believe that the use of daylight running lights leads drivers to be more oblivious of cars without lights on, and in any case there are any number of road hazards which are not illuminated.
The problem with studies regarding the effectiveness of daylight running lights in actually reducing the overall incidence of accidents is that there are many other variables in play, and the relatively small number of cars currently on the road that are so equipped. There is no question that they increase the frontal visibility of the car (and on that basis I would agree with the sentiment expressed by Q.E.D. that the marginal cost of the system is justified) but to what extent that impacts overall driver awareness and accident avoidance is difficult to quantify, particularly since many accidents are due to miscalculation of speed and distance (inexperienced drivers), impairment of judgement and perception (DUI), and blythe inattentiveness (cell phone use, passenger disruption, et cetera). Still, a cursory survey of the literature shows that a majority of studies indicate some positive level of result, albeit not without contest.
Stranger
I for one would like to see studies that correlate the use of DRL’s with the type of road and the amount of traffic. Driving in downtown Toronto (where DRL’s are required on Canadian vehicles) the idea of DRL’s preventing accidents is stupid. Likewise on I-94 in Detroit, what the heck is the use? On the other hand, on roads where there’s no a whole lot of traffic, or where there are curves, hills, or other conditions that may make a car less noticeable, there seems to be a lot more value.
Personal observation. When you have a number of cars coming towards you, it is easy to pick out the ones with headlights on, so easy that you can end up focusing on the headlights and not the cars per se.
The point of DRLs is to make picking out the cars in you field of view easier. If people stop looking as carefully to see cars because they can see most of them easily, it’s not hard to imagine that cars without lights on would be less likely to be noticed.
I could swear Cecil did a piece on DRLs in which he said that they don’t really do any good, but I can’t find it.
The rationale for them in Sweden was that there are very few hours of daylight in the long winter months but enough light to see to drive by. As in the US, there are may low populated areas where you can drive for hours without seeing another car, on excellent roads that permit driving at high speeds. These roads typically run through forests that decrease visibility even further.
An indistinct looking car - grey, dark blue and especially green, can be very hard to spot before it is too late but a point of light stands out - like a beacon.
In conditions of reduced visibility DLRs make a significant difference - They are sometimes more visible that the directional beam of a headlamp if you are off-axis. Again this is a significant factor in Sweden where it used to be, don’t know if this still applies, that you can drive straight out from a side road onto the main carriageway and traffic approaching from the right had to give way. Never got the logic of that but you ignore it at your peril.
Things have changed in the UK considerably and the majority of drivers use their headlights during the daytime much more, when I first came back here it used to piss people off considerably that the DLRs on my Volvo were on all the time, I used to get honked and flashed at all the time. Never happens any more now.
I would agree that DLRs are not really such a benifit in urban areas where you are naturally more watchful of other traffic. They don’t do any harm though so they may as well be there.