Actually 2 studies were done that showed DRL reduce some accidents by 3%. Opponents of DRL say this is not worth it. I agree if you are in the other 97%. They also say you use more gas and studies have shown this to equal about $3 per year. Which is a lot when you multiply this times the number of cars on the road.

I believe they add a measure of safety but may not be perticularly good for the environment.