DRL's were extensively tested in the USA, especially for accident reduction. The results are why they are not federally required, and the drawbacks could be even worse, as reported here. DRL's are not headlights, they are much dimmer. Here in MT we do have some sections of road where headlights are recommended, might even be required, one of them is the road from Livingston to YNP, a very high accident area. I remember MANY truck fleets, for many years, had "Lights On For Safety" painted on them. Full brightness headlights are the way to go.