__ Light, Red, Green Lights for Vehicle Flow
This page is the CodyCross answer for the clue below from Physics, Group 1890, Puzzle 5 (X-Ray Machine).
Question is: __ Light, Red, Green Lights for Vehicle Flow
and the answer is: TRAFFIC
Word Meaning:
TRAFFIC — Moving pedestrians or vehicles, or the flux or passage thereof.
Definitions from Wiktionary.