Street Lights (Flow & Turn Arrows)

Factual Questions
1

I am looking for safety or traffic flow improvement research/information regarding turn arrow programming.

Setup: East/West major interstate intersecting a minor North/South road with little in either direction. E/W highway has a seperate lane on each side for E/W turning controlled by a turn arrow indicator. Previously both turning lanes would (even when unoccupied) be green before E/W traffic commenced.
A new change has made the E-bound lane turn arrow green along with E-bound traffic only. After 8 seconds or so the E-N turn arrow is red and W-bound traffic begins. The E/W-bound stays green for up to 4 minutes and finally the W-South arrow greens as the E-bound traffic is Red. After the alloted time the N/S traffic greens and the cycle repeats.

Why would this type of change be made? Is it safety related? Traffic flow?
I have noticed this type of pattern being used at intersections of major highways…but why in this instance?

2

Local traffic engineers probably perform several studies and determine the most efficient and safest lights sequence. At least that’s what they do where I live.

3

As Duckster said, if the major direction begins experiencing unacceptable delays at the signal, a traffic study is done and the signal timings adjusted accordingly. The study may be a simple car-counting done by people standing at the intersection or it might involve automated traffic counting devices and complex computer modeling. It all depends upon the complexity of the intersection and the funds available to conduct the study.