Cobb County Government

Why does the County not operate traffic signals in flash late at night or in light traffic times?

The Department does not operate traffic signals in “flash mode” for the following reasons:

  1. Standard traffic engineering practice is to only flash signals for emergency conditions, or prior to a new installation. An emergency condition can occur when the electronic monitor detects a problem with the traffic signal controller and automatically places the traffic signal in flash mode.
  2. In general, the traveling public recognizes the signal flash mode as a malfunction and not as normal operation.
  3. The traveling public is unclear on how to travel through a signal in flash mode; some treat the condition as an all-way stop and others as a side street stop; and as a result a safety risk is created and unnecessary traffic delays can occur.

Alternatively, the Department accommodates side street traffic during light traffic conditions by operating signal systems in either a very short cycle length of approximately one minute, or by operating signals in “free mode” which permits a rapid change from the main street green to serve arriving side street traffic.