You might search the Congressional Record for the result of the test conducted for the US Senate
Vehicles passing on two lane roads is listed as just one of the reasons why the engineers, from several Universities that did the research for the US Senate, determined DRLs can be DANGEROUS.
The majority of drivers are accustomed to seeing headlamps, not the less dimly lit DRLs, and in that situation they tend to perceive the DRLs a headlamps and thus judge the distance between their vehicle and the approaching vehicle as being far greater than it actually is, leading to a head-on collision.
Every state requires the use of headlamps during times of limited vision and it is common around here in Pennsylvania to see the State Police stopping Canadian drivers traveling I-81, relying on only DRLs, when they should be using headlamps such as at dusk or in fog.
mike