Traffic signal borders (retroreflective).

The US Federal Highway Administration (FHWA) reports a 15% reduction in total crashes to traffic signals fitted with backing boards and retroreflective borders.

Signal heads that have backing boards equipped with retroreflective borders are more visible and conspicuous in both daytime and nighttime conditions, highlight the signals during periods of power outages when the signals would otherwise be dark, and are claimed to provide advantages for both older and color vision deficient drivers.

The FWHA’s base their crash reduction factor on the research of Sayed et al (2005).