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Did You Know? What To Do When a Signal Is In Flash

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By: Jeremy Greer, P.E., from Sain Associates blog

Traffic signals are part of daily life for most U.S. citizens.  Traffic signals are commonly seen at roadway intersections and primarily function to assign the right-of-way to the various traffic movements.  A traffic signal uses three colors, directional arrows, and circular indications to convey certain messages to drivers.  When signals work as normal, most drivers get the message.

What about when a signal is not working correctly, how should it be treated? When it’s ‘flashing’ (yellow/red)? When it’s completely dark (no red/yellow/green lights show at all)?  As someone that commutes approximately 120 miles each weekday, my experience is there is no consensus amongst drivers, law enforcement personnel, or municipal agencies.  There is MUCH CONFUSION!  Some stop, some go, some yell, some curse, and some hit the horn to express dismay! Let’s dig a little…

First let’s distinguish between two separate conditions:

  1. ‘Flashing Mode’ is when a signal flashes or ‘blinks’ certain signal faces for certain movements.  (You may see this when a thunderstorm causes power outages, and the traffic signal battery backup takes over.) The major street sees flashing circular yellow, and the side street sees flashing circular red.
    • ‘Flashing Mode’ is typically the default safe-mode.  The signal cannot operate normally, but by flashing, it is attempting to provide some basic level of order at the intersection.  ‘Flashing Mode’ is deliberate and intentional in both signal design and construction.
    • A signal is ‘out’ or ‘dark’ when there is no power, and none of the signal faces are illuminated and, therefore, not conveying a message to drivers.

What agency or group determines how we handle the situation and what do they say?

Let’s start nationally and work down to a state and local level.

  • Manual on Uniform Traffic Control Devices (MUTCD)
    • Federal law mandates that the MUTCD is the national standard for all traffic control devices on any road open to public travel (23 CFR 655, Subpart F), and all devices in all states shall be in substantial conformance.
    • Definitions (Paraphrased) – [MUTCD 2009 Section 4D.04]:
      • Flashing Circular Red – stop before entering intersection…then, the right to proceed shall be the same as if at a stop sign.
      • Flashing Circular Yellow – cautiously enter the intersection to proceed through or make a turn…
  • The Code of Alabama 1975
    • Section 32-5A-34:
      • (a)(1)-Flashing red (stop signal) – stop before entering intersection…then, the right to proceed shall be the same as if at a stop sign
      • (a)(2)-Flashing yellow (caution signal) – may proceed through the intersection or past such signal only with caution.
  • Local Laws 
    • Vary…but most reference the Federal or State level adopted MUTCD

So, federal, state, and local legislation seem to agree on the definition of ‘flashing yellow’ and ‘flashing red’ and how drivers should respond to these messages.  Ask the licensed drivers you know, and probably all will say they know the meaning of ‘flashing yellow’ and ‘flashing red.’  So, why the confusion when the situation arises?

I think there are several factors.  I believe local media is a contributing factor.  Traffic reports on local radio and television outlets often instruct the audience to ‘treat malfunctioning traffic signals as a 4-way stop’.  So, does it boil down to each individual’s definition of ‘malfunctioning’?  In your opinion, is a signal malfunctioning when it’s ‘flashing’ or when it’s ‘dark’?

I think driver expectation is a major factor.  Drivers respond in different ways.  As delay and frustration increase on the side street, drivers may become more aggressive, less apt to wait, and take small gaps or cut off other drivers.  Drivers on the major street see this behavior and decide that stopping at a flashing yellow is the safe decision for them personally (or it’s the Good Samaritan mentality).  Does that then become the natural response to similar future incidents?  I understand the personal safety logic.

I bring this up as a safety issue.  When a signal is on flash under heavy traffic, inconsistent driver behavior escalates the risk.  It seems many drivers react in opposition to the current law.  And there’s no doubt that stopping could easily fall under ‘proceed with caution.’  Is it time to re-evaluate this scenario and default to an all-way stop?  How do we support a more consistent behavior?

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