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I'm looking to buy a car for the first time, and I see the option to have a Daytime Running Lights. What are they for, and do I need them? I live in Los Angeles, where the the two seasons that do not exist are winter and football. This car will be used for city and freeway driving.
TL;DR -- What are DRLs for, and do I need them for city driving?
The short answer is: they're for other people.
Here's a practical example: I drive a black car. In the late summer, the trees around my neighborhood really overhang the road and block a lot of the lower-angle sunlight. Also, the roads near my house range from 10-20 residential roads to full highway speeds.
So, at a glance, my car doesn't passively give off a lot of visual cues about its orientation using the decreased ambient light. If you look, you can see that I'm definitely going 20, 40 or 60 mph but it might be just a little less clear out of the corner of your eye.
With the running lights, it's just a little more obvious. The human eye is great at picking up contrast and motion in the rod-dominated periphery of your vision.
All that said, they aren't a magic spell: if, say, you happen to be the kind of person who's talking on your cell phone, looking the other way while you cut me off in a parking lot (just to pose a not-so-hypothetical example), there's nothing that a couple of little lights on my car can do.
As the Wikipedia entry says, one benefit is that they improve visibility of the car. The idea is that they improve the safety of the vehicle. Although:
A 2008 study by the U.S. National Highway Traffic Safety Administration analysed the effect of DRLs on frontal and side-on crashes between two vehicles and on vehicle collisions with pedestrians, cyclists, and motorcyclists. The analysis determined that DRLs offer no statistically-significant reduction in the frequency or severity of the collisions studied, except for a reduction in light trucks' and vans' involvement in two-vehicle crashes by a statistically-significant 5.7%.
As Peter mentioned the primary benefit is safety by making your vehicle more visible to others. Therefore, it is more useful in a city than a rural area where you would have more people who need to see your vehicle.
Another advantage of daytime running lights, is that insurance companies typically give a discount on vehicles equipped with this option.
In some areas - I seem to recall Alaska, Arizona or somewhere similarly open - running lights are generally discouraged when the sun is relatively low in the sky as the accident rate was increased. The article reckoned the lights helped the car blend in with the sun's glare.
Some people promote Daytime Running Lights as a safety feature, but as with many ideas promoted in the name of road safety I have yet to see much evidence to support the assertion.
Also, while some study's show there are no benefits from increased visibility from DRL's on front impact scenarios, I wonder if anyone has studied the impact of daylight rear lights on rear impacts, due to there being less contrast between lit tail lights and brake lights (often in the same cluster) compared to unlit tail lights and brake lights. My hypothesis is that reduced contrast will result in slower reactions and a greater liklihood of a rear impact.
I understand that in some jurestictions, DRL has been made compulsary. Assuming that I would not be likely to drive in one of these locales, I would prefer to keep control of whether my vehicles lights are on or not - I certainly wouldn't pay for the option to have the choice removed from me.
