NMA DRL Fact Sheet ( PDF )
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In reviewing the literature related to the value of DRLs, “pro” DRL studies were regularly criticized for their failure to consider confounding results or other mitigating factors.

Increased fuel use and resulting emissions are modest on a per vehicle basis. However, multiplied by millions of vehicles, these amounts become significant, especially in light of the absence of proven off-setting benefits to the consumer.

While we understand the desire of automobile manufacturers to “harmonize” their product lines from country to country, the NMA believes the real negatives of hard-wired DRLs far outweigh the unproven and hypothetical advantages. The NMA generally supports the notion of “consumer choice” as it relates to vehicle equipment. However, it is not the purchaser of a DRL-equipped vehicle who suffers the immediate consequences of DRL operation (other than fuel utilization and electrical system maintenance), but rather the other motorists who are subject to the glare and distraction of DRLs.

The reasons to oppose daytime running lights can be summarized as follows:

1) They increase visual glare.
Headlight glare from both oncoming and following vehicles is the most common complaint registered with our office. General Motors vehicles are the most often cited sources of DRL glare. Reported motorists’ responses include the use of nighttime rear view mirror settings during daylight hours, maladjustment of external rear view mirrors, and the use of sun glasses even during low light and cloudy conditions. The most frequently cited reaction is one of “aggravation” or “irritation.” All the aforementioned add additional stress to the task of driving, resulting in shorter tempers and less attention paid to the task of driving. Also, the maladjustment of rear view mirrors means they are not able to serve the purposes for which they are intended thereby increasing the likelihood of an accident.

2) They obscure the directional signal lights.
DRLs are blamed for reducing or obscuring the visibility of directional signal lights.

3) They increase visual clutter.
Rather than simply increasing conspicuity, multiple vehicles with DRLs are found to be distracting and adding an element of confusion to otherwise normal traffic flow.

4) They mask other roadway users
DRLs dominate visual attention to the exclusion and disadvantage of pedestrians, bicyclists, highway workers, and other vehicles that do not have DRLs.

5) They reduce the conspicuity of motorcycles.
Many motorcyclists feel that the conspicuity of their smaller vehicles is increased by operating with their headlights on during daylight hours. There is concern that the widespread use of DRLs on automobiles will eliminate the (assumed) value of daytime headlight use by motorcyclists.

6) They distort distance perception.
Complaints of distorted distance perception vary. Certain individuals claim DRLs make on-coming vehicles appear closer than they really are. Others people make the opposite claim. What is consistent is that DRLs distort distance perception.

7) They reduce emergency vehicle conspicuity.
Daytime use of various lighting systems serve to distinguish emergency vehicles from other traffic on public roadways. This differentiation is diminished (if not eliminated) by large concentrations of DRL-equipped vehicles. This is also a concern for convoys of slow moving vehicles and special circumstances such as funeral processions where groups of vehicles are not moving in sync with normal traffic flow.

8) They can discourage motorists from using standard lights.
Because DRLs provide a degree of forward lighting, many motorists fail to turn on their standard lights in low-light, low-visibility situations. This means the rear lights of certain vehicles are not illuminated. We believe DRL use increases the probability of rear end collisions. The potential for daytime tail light use to mask brake lights has already been recognized, as evidenced by DRL circuitry that excludes activation of tail lights.

Ultimately, the fact remains that any motorist who feels the need for greater conspicuity has the ability, immediately at hand, to turn on his or her headlights. This is not a task that can be classed as arduous, difficult or confusing.