Daytime Running Lights and Bicycle Visibility

Car Headlights


Most of the time, I travel by bike or by foot. For many years, I used a bike as my sole means of transportation. When the weather was too harsh, or there was nowhere to lock my bike, I resorted to public transportation.

Eventually, this arrangement didn’t entirely meet my needs. I had to travel farther than was reasonable by bike and to locations where no public transportation was available.

At that point, I made the decision to buy a car. As one who isn’t part of America’s car-centric culture, I wanted a basic car, just to carry me to my destination. I set a modest budget for the purchase and prioritized good gas mileage, durability, and low maintenance.

I hadn’t been car shopping for a long time. To my surprise, things had changed quite a bit. Among the advances in auto technology was a feature called daytime running lights.

The car salesperson explained to me that this innovation was designed to make cars more visible during the daytime. Crash data showed fewer accidents for cars traveling with their headlights on during the daytime. So auto manufacturers had decided to offer this feature on certain models of their cars.

One day, not long after I bought this car, I was out on my bike at dusk when I noticed many cars driving without headlights. I was baffled by this. These were expensive cars, which should have had all of the latest features.

My inexpensive car was designed to turn on the headlights automatically when I started the car. At night, a light sensor would turn on the interior lights and brighten the headlights. Why then, I wondered, were cars driving around without their headlights on?

Once I had noticed this, I began watching car headlights at dusk and at night. A surprisingly high percentage of cars did not have their headlights on, even when it became dark.

It was much more difficult to see these cars approaching while riding my bike. My headlight’s beam wasn’t bright enough to illuminate the cars until they were very close to me. And, I couldn’t anticipate their movements. Unless they happened to use their turn signals, I had no way of knowing their intentions. More than once, without warning, a lightless car had turned left in front of me.

If I couldn’t see these unilluminated cars, their ability to see me, on a bicycle, would be as bad, if not worse.

Before noticing this phenomenon, I had thought myself rather visible. To make myself visible, I always turned on my bicycle headlight at dusk. My rear flashing light ran day and night.

Still, it didn’t seem possible for oncoming drivers, without headlights, to identify my small headlight as belonging to a bicycle. And, all of my reflective gear was useless — despite the beliefs of many police officers who see reflective gear as the only way for cyclists to avoid getting hit by cars. Reflective gear will only glow when viewed directly in the beam of a headlight.

The more I thought about it, the more convinced I became of the value of daytime running lights. Out of curiosity, I looked for a regulation requiring American cars to have daytime running lights.

Other countries had this requirement, I learned, but not the U.S. No wonder so many luxury cars were driving around at night without lights.

What was most strange about this was the reasoning. Although opponents have cited increased fuel consumption as the reason not to mandate daytime running lights, their assumptions aren’t accurate.

“To figure out how much extra gasoline the United States would use if all 244 million cars on its roads were equipped with mandatory DRLs, we’ll have to make a few assumptions [source: DOT]. First, we’ll assume that DRLs would average out at about 90 watts total — roughly between the low and the high wattage capabilities, and that the fuel penalty therefore would probably be mid-range as well: about 1 percent. With the help of a graph provided by the Federal Highway Administration, we can see that of the 7 billion miles (11.3 billion kilometers) Americans drive every day, approximately 70 percent of those are driven during daylight hours, which equals about 4.9 billion miles (7.9 billion kilometers) driven during the time when DRLs would be in use. [source: EIA, DOT].

Since the average consumer car in the United States gets about 20.3 miles (32.6 kilometers) per gallon, that means Americans currently use about 241.4 million gallons of gas for driving during daylight hours. To get that number, we divided the number of miles driven throughout the day by the average car’s fuel efficiency (4.9 billion miles divided by 20.3 mpg) [source: DOT]. Now, when we factor in the 1 percent reduction in fuel efficiency, that usage increases to 243.9 million gallons — a difference of more than 2 million gallons.
At current U.S. prices ($3.81 per gallon as of August 2008), that would be a total of more than $7.62 million every day [source: EIA]. Of course, when you divide that by the number of cars on the road, it’s not even a penny per car. So if you want to contest the purpose of a DRL law, you’re going to need more up your sleeve than fuel consumption.”

Some opponents have also cited glare as a problem with daytime running lights, but low intensity lights have been developed to eliminate glare. Therefore, the decision about whether to use daytime running lights rests upon the value of the safety benefits.

As far as cyclists are concerned, one of the biggest problems they face on the road is making themselves visible. During the day, their visibility is reduced when riding in the shade. And, at dusk, the semi-darkness reduces their visibility even more. These are the conditions under which cars driving without headlights will have the most trouble seeing bicycles.

When it comes to bicycle safety, we tend to focus on things such as providing bicycle lanes to segregate bikes from cars. But there are other steps we could take to safely integrate bicycles into American roads.

If fuel consumption isn’t greatly increased, and glare can be reduced, making daytime running lights mandatory would be one way to improve bicycle safety. Alternatively, light sensors could be made mandatory on all cars for the purpose of automatically turning headlights on at dusk.

Generally speaking, road safety needs to be evaluated from multiple perspectives if we are ever going to make sharing the road among various vehicles a reality.

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3 Responses to Daytime Running Lights and Bicycle Visibility

  1. Rebecca says:

    Car headlights & rear lights are big and can easily be seen from a distance. Bicycle lights are pinpoints of lights by comparison. Even the very bright ones are significantly smaller than car lights. I’m always checking this out when I am driving my car at night. The little lights that are cheap can barely be seen. I don’t think bicyclists realizes how barely visible they are. I would like to find lights for my bike that are as big as car lights!

    • I completely agree with you. I have an expensive headlight, which is very bright. Even so, it still looks like a pinpoint of light to oncoming traffic. To supplement it, I use another, smaller, flashing white light to draw attention to myself.

      In spite of my lights and reflective gear, I ride with the assumption that cars don’t see me. A different kind of bicycle light should be designed, with the goal of making the light identifiable as belonging to a bicycle – just as two headlights identify a motor vehicle.

  2. I developed my own bike lighting system a while ago. I’m currently redesigning into to incorporate more features and a better hardware design:

    My issue with DRLs is that they take focus away from smaller things such as motorcycles (which used to be the only vehicle on the road with lights on during the day), bicycles, and pedestrians. In bright sunlight, the dim state of these lights does absolutely nothing to illuminate objects in front or provide more visibility.

    While automatic lights are great for ensuring car lights on in the dark, they actually make driving in conditions such as rain very unsafe (and illegal in many places) because people forget to turn their lights on. Very few cars can automatically turn their lights on in the rain when it is still plenty bright outside, so it is up to the driver to do so. This is often forgotten because so many drivers rely on the car to do it automatically when it gets dark.

    I both drive and ride quite a bit. As a bicyclist, I don’t expect large vehicles to see me, so I am always on the defensive. Relying on a small flashing light will breed complacency. As a driver, I disdain many cyclists who ignore road signs and create many unsafe driving conditions, especially on narrow roads and around corners when I can’t see if there is any oncoming traffic but am stuck behind a cyclist climbing a hill in the middle of my (our) lane.

    As for some pulsing bike lights – cyclists will swear by them, but I find them so incredibly distracting while driving. Often, I am in a semi-congested traffic area at night, going no faster (on average) than a group of cyclists along side the road. The problem is that there is this constant cloud of strobe lights in the corner of my eye that greatly distracts me from the rest of the road. I have witnessed a decent number of fender benders in this exact situation. A slower pulse is just as effective and much less distracting to drivers. However, if the light is bright enough (which few that I have seen actually are) a quick strobe rear light during the day can be very effective while not being too distracting due to the brightness of the daylight.

    I think a lot of the issues of visibility between drivers and cyclists is that they have never seen a situation with the other’s point of view. Drivers who don’t ride are not expecting a bike to be in the road, and riders who rarely drive are clueless as to what actually does increase their own visibility.

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