Left turn signals in TX

[Urban Prairie Schooner]

In the Houston area (and presumably elsewhere in TX), the left turn traffic signals have two red signal heads; the rest of the signal is configured normally. The left signal heads operate in tandem in all examples that I have seen. I have not seen this anywhere else and have no idea why this should be. Does anyone know why the red signal phase is configured in this manner?

[Road Hog]

In the Houston area (and presumably elsewhere in TX), the left turn traffic signals have two red signal heads; the rest of the signal is configured normally. The left signal heads operate in tandem in all examples that I have seen. I have not seen this anywhere else and have no idea why this should be. Does anyone know why the red signal phase is configured in this manner?

Probably this way in places where there are two left-turn lanes. This is commonplace in DFW.

[swbrotha100]

Does Texas use any red left-turn arrows? I don't remember seeing them much the few times I was visiting or passing through.

[txstateends]

Does Texas use any red left-turn arrows? I don't remember seeing them much the few times I was visiting or passing through.

There weren't hardly any in DFW 20 years ago.  Now, Dallas has quite a few red left arrows--not sure about the extent of them in other cities.

[signalman]

The double red is probably used to place emphasis on the red.  That's what I've always assumed it meant when I've seen it elsewhere.  I know I've seen double red in NC before.  Perhaps it was used incase one burns out? 

[blawp]

Houston has converted most of its double red balls to double red arrows within the last 2 years.