2007-04-30

Traffic light with camera has shorter yellow light

According to the Athens Banner-Herald, Larry Jernigan believes that the county government shortened the length of the yellow signal on the traffic light at West Broad Street and Alps Road when they installed a camera system to catch drivers running the red light. He is going to court to fight a ticket he received. The truth may not be so sinister, but the yellow light is indeed shorter there for West Broad Street than the yellow lights at other traffic lights on the same road where the speed limit is also the same, 40 m.p.h. The yellow lights at Sycamore Drive, Camellia Drive, and Holman Avenue are 4.0 seconds long. The yellow light at Rocksprings Street is also 4.0 seconds, even though the speed limit is lower, 35 m.p.h. The yellow light for West Broad Street drivers at Alps and Hawthorne is 3.8 seconds long, and this is the only light with a red light camera.

The shortest yellow light I observed was an arrow for eastbound traffic on Broad turning west onto Hawthorne. It stayed lit for just 2.9 seconds.

I measured these times with a videotape. The NTSC format uses 30 frames per second. (NTSC stands for National Television Standards Committee -- or Never Twice the Same Color.) I advanced my tape frame by frame and counted frames to determine the length of the yellow lights. Although the article reported that David Clark from the Athens-Clarke County Department of Transportation and Public Works said that the Alps-Hawthorne light for Broad Street is 3.9 seconds, the actual visible period is 3.8 seconds. (When the lights change, there is a dark period between each color, and it is possible that the equipment's measurement starts when the green light turns off, but I only counted the dark periods between yellows and reds. Even though most of the lights are LEDs, they still also fade on and off, so the first video frame of a light shows a dim light.

4 comments:

Model Consumer said...

Perhaps the court may see fit to consider your field work as evidence!

Adrian said...

I hope the municipal court realizes that this is an issue to at least work through. Humans program the traffic lights, and humans make mistakes.

Polusplagchnos said...

Sometimes intentionally.

Model Consumer said...

For the record, I just wanted to state that my original comment was completely sincere and in no way sarcastic. And I totally agree with the other two comments.