Where did the yellow lights go

Their XUV was snaking, though more like crawling, through the insane traffic of a nearly metropolitan city in the sun-bathed afternoon of late summer. The tiny trots were amazed and at times even engrossed in the shimmering delusions of grandeur. But the overall combination of heat and snail paced traffic was exhausting and draining. Kids were getting increasingly unruly. And her attempts to tame their rumbustiousness were all but defeated. Until the traffic lights. The XUV resounded with merry sounds of the good old nursery rhyme:

Red light Red light what do you say?
I say stop stop stop.

She prompted them to sing further:

Yellow light yellow light what do you say?

"But the lights are still red" whined the youngest.

"Wait wait wait" she finished and answered in same breath.

After halting at the red lights for about a couple of minutes, the traffic breathed again. So with excitement she encouraged them further:

Green light green light what do you say?
I say go go go.

The response of her kids was not as sonorous. "Mom, where did the yellow lights go"?
The question was suspended in the carbonated soot of the city.
The yellow lights had lost utility and meaning. The modus vivendi had no place for the pause and reflect button.
Perhaps it was time to change the rhyme.