Answer:
Increase
Explanation:
After a scientific research, carried out by both A.F Williams and K.A Lancaster, in 1995, with a title: "The prospects of daytime running lights for reducing vehicle crashes in the United States." These researchers, however, made various conclusions, one of which, amongst other things, stated that Daytime running lights INCREASE visual contrast between vehicles and their background, which enhance their noticeability and detectability.
Therefore, the correct answer is INCREASE.
