I recall it as
Think
Stop
Look
Listen
Keep Thinking
Think: is this a safe place to cross? Can I see the road, can the drivers see me?
Look: right-left-right
Listen: can I hear traffic coming?
Keep Thinking: is it safe? If so, cross, but keep looking, listening, and thinking.
As well as judgung relative speeds, children need the fairly sophisticated skills of seeing things from another person's perspective, and of multi-tasking, in order to put the GCC into action.
And their are all sorts of other things to take into account, such as understanding that wearing a hood can obstruct your vision, and that rain can affect drivers.
I have not come across any book that deals with all these things satisfactorily (doesn't mean there isn't one, of course) and I feel some of the 'training help' has actually been dangerous. At dd's school actors performed a show at assembly, intended to teach children the GCC. Result: dd 'performs' the GCC, with no genuine understanding. She knows the words and understands in theory what she has to do, but does it as a dance, doing the movements by rote without actually doing the looking, listening, thinking. She's nearly 9, and I still wouldn't trust her to cross alone. I see her shading her eyes and looking sincerely around - but her eyes are not taking inwhat she sees. Then she curls her hand around her ear and scans gracefully from side to side - all the time oblivious to the cars approaching.
I'm still working on it with her.