In the late 50's or early 60's Greyhound ran their coach's with headlights on. There was a significant ( to them ) reduction in their accident rate. At that time only motorcycles had lights on in daylight.
There were so few vehicles using DRLs that it caught everyone's attention. Today with so many vehicles with DLRs on, the impact has probably lessened considerately.
It's similar to," If every one is special, no one is special ". The impact is not the same.
Ron